Quelle xlogrecovery.c Sprache: unbekannt

/*-------------------------------------------------------------------------
*
* xlogrecovery.c
*  Functions for WAL recovery, standby mode
*
* This source file contains functions controlling WAL recovery.
* InitWalRecovery() initializes the system for crash or archive recovery,
* or standby mode, depending on configuration options and the state of
* the control file and possible backup label file.  PerformWalRecovery()
* performs the actual WAL replay, calling the rmgr-specific redo routines.
* FinishWalRecovery() performs end-of-recovery checks and cleanup actions,
* and prepares information needed to initialize the WAL for writes.  In
* addition to these three main functions, there are a bunch of functions
* for interrogating recovery state and controlling the recovery process.
*
*
* Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/backend/access/transam/xlogrecovery.c
*
*-------------------------------------------------------------------------
*/

#include "postgres.h"

#include <ctype.h>
#include <math.h>
#include <time.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <unistd.h>

#include "access/timeline.h"
#include "access/transam.h"
#include "access/xact.h"
#include "access/xlog_internal.h"
#include "access/xlogarchive.h"
#include "access/xlogprefetcher.h"
#include "access/xlogreader.h"
#include "access/xlogrecovery.h"
#include "access/xlogutils.h"
#include "backup/basebackup.h"
#include "catalog/pg_control.h"
#include "commands/tablespace.h"
#include "common/file_utils.h"
#include "miscadmin.h"
#include "nodes/miscnodes.h"
#include "pgstat.h"
#include "postmaster/bgwriter.h"
#include "postmaster/startup.h"
#include "replication/slot.h"
#include "replication/slotsync.h"
#include "replication/walreceiver.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/latch.h"
#include "storage/pmsignal.h"
#include "storage/procarray.h"
#include "storage/spin.h"
#include "utils/datetime.h"
#include "utils/fmgrprotos.h"
#include "utils/guc_hooks.h"
#include "utils/pgstat_internal.h"
#include "utils/pg_lsn.h"
#include "utils/ps_status.h"
#include "utils/pg_rusage.h"

/* Unsupported old recovery command file names (relative to $PGDATA) */
#define RECOVERY_COMMAND_FILE "recovery.conf"
#define RECOVERY_COMMAND_DONE "recovery.done"

/*
* GUC support
*/
const struct config_enum_entry recovery_target_action_options[] = {
{"pause", RECOVERY_TARGET_ACTION_PAUSE, false},
{"promote", RECOVERY_TARGET_ACTION_PROMOTE, false},
{"shutdown", RECOVERY_TARGET_ACTION_SHUTDOWN, false},
{NULL, 0, false}
};

/* options formerly taken from recovery.conf for archive recovery */
char    *recoveryRestoreCommand = NULL;
char    *recoveryEndCommand = NULL;
char    *archiveCleanupCommand = NULL;
RecoveryTargetType recoveryTarget = RECOVERY_TARGET_UNSET;
bool  recoveryTargetInclusive = true;
int   recoveryTargetAction = RECOVERY_TARGET_ACTION_PAUSE;
TransactionId recoveryTargetXid;
char    *recovery_target_time_string;
TimestampTz recoveryTargetTime;
const char *recoveryTargetName;
XLogRecPtr recoveryTargetLSN;
int   recovery_min_apply_delay = 0;

/* options formerly taken from recovery.conf for XLOG streaming */
char    *PrimaryConnInfo = NULL;
char    *PrimarySlotName = NULL;
bool  wal_receiver_create_temp_slot = false;

/*
* recoveryTargetTimeLineGoal: what the user requested, if any
*
* recoveryTargetTLIRequested: numeric value of requested timeline, if constant
*
* recoveryTargetTLI: the currently understood target timeline; changes
*
* expectedTLEs: a list of TimeLineHistoryEntries for recoveryTargetTLI and
* the timelines of its known parents, newest first (so recoveryTargetTLI is
* always the first list member).  Only these TLIs are expected to be seen in
* the WAL segments we read, and indeed only these TLIs will be considered as
* candidate WAL files to open at all.
*
* curFileTLI: the TLI appearing in the name of the current input WAL file.
* (This is not necessarily the same as the timeline from which we are
* replaying WAL, which StartupXLOG calls replayTLI, because we could be
* scanning data that was copied from an ancestor timeline when the current
* file was created.)  During a sequential scan we do not allow this value
* to decrease.
*/
RecoveryTargetTimeLineGoal recoveryTargetTimeLineGoal = RECOVERY_TARGET_TIMELINE_LATEST;
TimeLineID recoveryTargetTLIRequested = 0;
TimeLineID recoveryTargetTLI = 0;
static List *expectedTLEs;
static TimeLineID curFileTLI;

/*
* When ArchiveRecoveryRequested is set, archive recovery was requested,
* ie. signal files were present.  When InArchiveRecovery is set, we are
* currently recovering using offline XLOG archives.  These variables are only
* valid in the startup process.
*
* When ArchiveRecoveryRequested is true, but InArchiveRecovery is false, we're
* currently performing crash recovery using only XLOG files in pg_wal, but
* will switch to using offline XLOG archives as soon as we reach the end of
* WAL in pg_wal.
*/
bool  ArchiveRecoveryRequested = false;
bool  InArchiveRecovery = false;

/*
* When StandbyModeRequested is set, standby mode was requested, i.e.
* standby.signal file was present.  When StandbyMode is set, we are currently
* in standby mode.  These variables are only valid in the startup process.
* They work similarly to ArchiveRecoveryRequested and InArchiveRecovery.
*/
static bool StandbyModeRequested = false;
bool  StandbyMode = false;

/* was a signal file present at startup? */
static bool standby_signal_file_found = false;
static bool recovery_signal_file_found = false;

/*
* CheckPointLoc is the position of the checkpoint record that determines
* where to start the replay.  It comes from the backup label file or the
* control file.
*
* RedoStartLSN is the checkpoint's REDO location, also from the backup label
* file or the control file.  In standby mode, XLOG streaming usually starts
* from the position where an invalid record was found.  But if we fail to
* read even the initial checkpoint record, we use the REDO location instead
* of the checkpoint location as the start position of XLOG streaming.
* Otherwise we would have to jump backwards to the REDO location after
* reading the checkpoint record, because the REDO record can precede the
* checkpoint record.
*/
static XLogRecPtr CheckPointLoc = InvalidXLogRecPtr;
static TimeLineID CheckPointTLI = 0;
static XLogRecPtr RedoStartLSN = InvalidXLogRecPtr;
static TimeLineID RedoStartTLI = 0;

/*
* Local copy of SharedHotStandbyActive variable. False actually means "not
* known, need to check the shared state".
*/
static bool LocalHotStandbyActive = false;

/*
* Local copy of SharedPromoteIsTriggered variable. False actually means "not
* known, need to check the shared state".
*/
static bool LocalPromoteIsTriggered = false;

/* Has the recovery code requested a walreceiver wakeup? */
static bool doRequestWalReceiverReply;

/* XLogReader object used to parse the WAL records */
static XLogReaderState *xlogreader = NULL;

/* XLogPrefetcher object used to consume WAL records with read-ahead */
static XLogPrefetcher *xlogprefetcher = NULL;

/* Parameters passed down from ReadRecord to the XLogPageRead callback. */
typedef struct XLogPageReadPrivate
{
int   emode;
bool  fetching_ckpt; /* are we fetching a checkpoint record? */
bool  randAccess;
TimeLineID replayTLI;
} XLogPageReadPrivate;

/* flag to tell XLogPageRead that we have started replaying */
static bool InRedo = false;

/*
* Codes indicating where we got a WAL file from during recovery, or where
* to attempt to get one.
*/
typedef enum
{
XLOG_FROM_ANY = 0,   /* request to read WAL from any source */
XLOG_FROM_ARCHIVE,   /* restored using restore_command */
XLOG_FROM_PG_WAL,   /* existing file in pg_wal */
XLOG_FROM_STREAM,   /* streamed from primary */
} XLogSource;

/* human-readable names for XLogSources, for debugging output */
static const char *const xlogSourceNames[] = {"any", "archive", "pg_wal", "stream"};

/*
* readFile is -1 or a kernel FD for the log file segment that's currently
* open for reading.  readSegNo identifies the segment.  readOff is the offset
* of the page just read, readLen indicates how much of it has been read into
* readBuf, and readSource indicates where we got the currently open file from.
*
* Note: we could use Reserve/ReleaseExternalFD to track consumption of this
* FD too (like for openLogFile in xlog.c); but it doesn't currently seem
* worthwhile, since the XLOG is not read by general-purpose sessions.
*/
static int readFile = -1;
static XLogSegNo readSegNo = 0;
static uint32 readOff = 0;
static uint32 readLen = 0;
static XLogSource readSource = XLOG_FROM_ANY;

/*
* Keeps track of which source we're currently reading from. This is
* different from readSource in that this is always set, even when we don't
* currently have a WAL file open. If lastSourceFailed is set, our last
* attempt to read from currentSource failed, and we should try another source
* next.
*
* pendingWalRcvRestart is set when a config change occurs that requires a
* walreceiver restart.  This is only valid in XLOG_FROM_STREAM state.
*/
static XLogSource currentSource = XLOG_FROM_ANY;
static bool lastSourceFailed = false;
static bool pendingWalRcvRestart = false;

/*
* These variables track when we last obtained some WAL data to process,
* and where we got it from.  (XLogReceiptSource is initially the same as
* readSource, but readSource gets reset to zero when we don't have data
* to process right now.  It is also different from currentSource, which
* also changes when we try to read from a source and fail, while
* XLogReceiptSource tracks where we last successfully read some WAL.)
*/
static TimestampTz XLogReceiptTime = 0;
static XLogSource XLogReceiptSource = XLOG_FROM_ANY;

/* Local copy of WalRcv->flushedUpto */
static XLogRecPtr flushedUpto = 0;
static TimeLineID receiveTLI = 0;

/*
* Copy of minRecoveryPoint and backupEndPoint from the control file.
*
* In order to reach consistency, we must replay the WAL up to
* minRecoveryPoint.  If backupEndRequired is true, we must also reach
* backupEndPoint, or if it's invalid, an end-of-backup record corresponding
* to backupStartPoint.
*
* Note: In archive recovery, after consistency has been reached, the
* functions in xlog.c will start updating minRecoveryPoint in the control
* file.  But this copy of minRecoveryPoint variable reflects the value at the
* beginning of recovery, and is *not* updated after consistency is reached.
*/
static XLogRecPtr minRecoveryPoint;
static TimeLineID minRecoveryPointTLI;

static XLogRecPtr backupStartPoint;
static XLogRecPtr backupEndPoint;
static bool backupEndRequired = false;

/*
* Have we reached a consistent database state?  In crash recovery, we have
* to replay all the WAL, so reachedConsistency is never set.  During archive
* recovery, the database is consistent once minRecoveryPoint is reached.
*
* Consistent state means that the system is internally consistent, all
* the WAL has been replayed up to a certain point, and importantly, there
* is no trace of later actions on disk.
*
* This flag is used only by the startup process and postmaster. When
* minRecoveryPoint is reached, the startup process sets it to true and
* sends a PMSIGNAL_RECOVERY_CONSISTENT signal to the postmaster,
* which then sets it to true upon receiving the signal.
*/
bool  reachedConsistency = false;

/* Buffers dedicated to consistency checks of size BLCKSZ */
static char *replay_image_masked = NULL;
static char *primary_image_masked = NULL;

/*
* Shared-memory state for WAL recovery.
*/
typedef struct XLogRecoveryCtlData
{
/*
  * SharedHotStandbyActive indicates if we allow hot standby queries to be
  * run.  Protected by info_lck.
*/
bool  SharedHotStandbyActive;

/*
  * SharedPromoteIsTriggered indicates if a standby promotion has been
  * triggered.  Protected by info_lck.
*/
bool  SharedPromoteIsTriggered;

/*
  * recoveryWakeupLatch is used to wake up the startup process to continue
  * WAL replay, if it is waiting for WAL to arrive or promotion to be
  * requested.
  *
  * Note that the startup process also uses another latch, its procLatch,
  * to wait for recovery conflict. If we get rid of recoveryWakeupLatch for
  * signaling the startup process in favor of using its procLatch, which
  * comports better with possible generic signal handlers using that latch.
  * But we should not do that because the startup process doesn't assume
  * that it's waken up by walreceiver process or SIGHUP signal handler
  * while it's waiting for recovery conflict. The separate latches,
  * recoveryWakeupLatch and procLatch, should be used for inter-process
  * communication for WAL replay and recovery conflict, respectively.
*/
Latch  recoveryWakeupLatch;

/*
  * Last record successfully replayed.
*/
XLogRecPtr lastReplayedReadRecPtr; /* start position */
XLogRecPtr lastReplayedEndRecPtr; /* end+1 position */
TimeLineID lastReplayedTLI; /* timeline */

/*
  * When we're currently replaying a record, ie. in a redo function,
  * replayEndRecPtr points to the end+1 of the record being replayed,
  * otherwise it's equal to lastReplayedEndRecPtr.
*/
XLogRecPtr replayEndRecPtr;
TimeLineID replayEndTLI;
/* timestamp of last COMMIT/ABORT record replayed (or being replayed) */
TimestampTz recoveryLastXTime;

/*
  * timestamp of when we started replaying the current chunk of WAL data,
  * only relevant for replication or archive recovery
*/
TimestampTz currentChunkStartTime;
/* Recovery pause state */
RecoveryPauseState recoveryPauseState;
ConditionVariable recoveryNotPausedCV;

slock_t  info_lck;  /* locks shared variables shown above */
} XLogRecoveryCtlData;

static XLogRecoveryCtlData *XLogRecoveryCtl = NULL;

/*
* abortedRecPtr is the start pointer of a broken record at end of WAL when
* recovery completes; missingContrecPtr is the location of the first
* contrecord that went missing.  See CreateOverwriteContrecordRecord for
* details.
*/
static XLogRecPtr abortedRecPtr;
static XLogRecPtr missingContrecPtr;

/*
* if recoveryStopsBefore/After returns true, it saves information of the stop
* point here
*/
static TransactionId recoveryStopXid;
static TimestampTz recoveryStopTime;
static XLogRecPtr recoveryStopLSN;
static char recoveryStopName[MAXFNAMELEN];
static bool recoveryStopAfter;

/* prototypes for local functions */
static void ApplyWalRecord(XLogReaderState *xlogreader, XLogRecord *record, TimeLineID *replayTLI);

static void EnableStandbyMode(void);
static void readRecoverySignalFile(void);
static void validateRecoveryParameters(void);
static bool read_backup_label(XLogRecPtr *checkPointLoc,
         TimeLineID *backupLabelTLI,
         bool *backupEndRequired, bool *backupFromStandby);
static bool read_tablespace_map(List **tablespaces);

static void xlogrecovery_redo(XLogReaderState *record, TimeLineID replayTLI);
static void CheckRecoveryConsistency(void);
static void rm_redo_error_callback(void *arg);
#ifdef WAL_DEBUG
static void xlog_outrec(StringInfo buf, XLogReaderState *record);
#endif
static void xlog_block_info(StringInfo buf, XLogReaderState *record);
static void checkTimeLineSwitch(XLogRecPtr lsn, TimeLineID newTLI,
        TimeLineID prevTLI, TimeLineID replayTLI);
static bool getRecordTimestamp(XLogReaderState *record, TimestampTz *recordXtime);
static void verifyBackupPageConsistency(XLogReaderState *record);

static bool recoveryStopsBefore(XLogReaderState *record);
static bool recoveryStopsAfter(XLogReaderState *record);
static char *getRecoveryStopReason(void);
static void recoveryPausesHere(bool endOfRecovery);
static bool recoveryApplyDelay(XLogReaderState *record);
static void ConfirmRecoveryPaused(void);

static XLogRecord *ReadRecord(XLogPrefetcher *xlogprefetcher,
         int emode, bool fetching_ckpt,
         TimeLineID replayTLI);

static int XLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
       int reqLen, XLogRecPtr targetRecPtr, char *readBuf);
static XLogPageReadResult WaitForWALToBecomeAvailable(XLogRecPtr RecPtr,
               bool randAccess,
               bool fetching_ckpt,
               XLogRecPtr tliRecPtr,
               TimeLineID replayTLI,
               XLogRecPtr replayLSN,
               bool nonblocking);
static int emode_for_corrupt_record(int emode, XLogRecPtr RecPtr);
static XLogRecord *ReadCheckpointRecord(XLogPrefetcher *xlogprefetcher,
          XLogRecPtr RecPtr, TimeLineID replayTLI);
static bool rescanLatestTimeLine(TimeLineID replayTLI, XLogRecPtr replayLSN);
static int XLogFileRead(XLogSegNo segno, TimeLineID tli,
       XLogSource source, bool notfoundOk);
static int XLogFileReadAnyTLI(XLogSegNo segno, XLogSource source);

static bool CheckForStandbyTrigger(void);
static void SetPromoteIsTriggered(void);
static bool HotStandbyActiveInReplay(void);

static void SetCurrentChunkStartTime(TimestampTz xtime);
static void SetLatestXTime(TimestampTz xtime);

/*
* Initialization of shared memory for WAL recovery
*/
Size
XLogRecoveryShmemSize(void)
{
Size  size;

/* XLogRecoveryCtl */
size = sizeof(XLogRecoveryCtlData);

return size;
}

void
XLogRecoveryShmemInit(void)
{
bool  found;

XLogRecoveryCtl = (XLogRecoveryCtlData *)
  ShmemInitStruct("XLOG Recovery Ctl", XLogRecoveryShmemSize(), &found);
if (found)
  return;
memset(XLogRecoveryCtl, 0, sizeof(XLogRecoveryCtlData));

SpinLockInit(&XLogRecoveryCtl->info_lck);
InitSharedLatch(&XLogRecoveryCtl->recoveryWakeupLatch);
ConditionVariableInit(&XLogRecoveryCtl->recoveryNotPausedCV);
}

/*
* A thin wrapper to enable StandbyMode and do other preparatory work as
* needed.
*/
static void
EnableStandbyMode(void)
{
StandbyMode = true;

/*
  * To avoid server log bloat, we don't report recovery progress in a
  * standby as it will always be in recovery unless promoted. We disable
  * startup progress timeout in standby mode to avoid calling
  * startup_progress_timeout_handler() unnecessarily.
*/
disable_startup_progress_timeout();
}

/*
* Prepare the system for WAL recovery, if needed.
*
* This is called by StartupXLOG() which coordinates the server startup
* sequence.  This function analyzes the control file and the backup label
* file, if any, and figures out whether we need to perform crash recovery or
* archive recovery, and how far we need to replay the WAL to reach a
* consistent state.
*
* This doesn't yet change the on-disk state, except for creating the symlinks
* from table space map file if any, and for fetching WAL files needed to find
* the checkpoint record.  On entry, the caller has already read the control
* file into memory, and passes it as argument.  This function updates it to
* reflect the recovery state, and the caller is expected to write it back to
* disk does after initializing other subsystems, but before calling
* PerformWalRecovery().
*
* This initializes some global variables like ArchiveRecoveryRequested, and
* StandbyModeRequested and InRecovery.
*/
void
InitWalRecovery(ControlFileData *ControlFile, bool *wasShutdown_ptr,
    bool *haveBackupLabel_ptr, bool *haveTblspcMap_ptr)
{
XLogPageReadPrivate *private;
struct stat st;
bool  wasShutdown;
XLogRecord *record;
DBState  dbstate_at_startup;
bool  haveTblspcMap = false;
bool  haveBackupLabel = false;
CheckPoint checkPoint;
bool  backupFromStandby = false;

dbstate_at_startup = ControlFile->state;

/*
  * Initialize on the assumption we want to recover to the latest timeline
  * that's active according to pg_control.
*/
if (ControlFile->minRecoveryPointTLI >
  ControlFile->checkPointCopy.ThisTimeLineID)
  recoveryTargetTLI = ControlFile->minRecoveryPointTLI;
else
  recoveryTargetTLI = ControlFile->checkPointCopy.ThisTimeLineID;

/*
  * Check for signal files, and if so set up state for offline recovery
*/
readRecoverySignalFile();
validateRecoveryParameters();

/*
  * Take ownership of the wakeup latch if we're going to sleep during
  * recovery, if required.
*/
if (ArchiveRecoveryRequested)
  OwnLatch(&XLogRecoveryCtl->recoveryWakeupLatch);

/*
  * Set the WAL reading processor now, as it will be needed when reading
  * the checkpoint record required (backup_label or not).
*/
private = palloc0(sizeof(XLogPageReadPrivate));
xlogreader =
  XLogReaderAllocate(wal_segment_size, NULL,
         XL_ROUTINE(.page_read = &XLogPageRead,
           .segment_open = NULL,
           .segment_close = wal_segment_close),
         private);
if (!xlogreader)
  ereport(ERROR,
    (errcode(ERRCODE_OUT_OF_MEMORY),
     errmsg("out of memory"),
     errdetail("Failed while allocating a WAL reading processor.")));
xlogreader->system_identifier = ControlFile->system_identifier;

/*
  * Set the WAL decode buffer size.  This limits how far ahead we can read
  * in the WAL.
*/
XLogReaderSetDecodeBuffer(xlogreader, NULL, wal_decode_buffer_size);

/* Create a WAL prefetcher. */
xlogprefetcher = XLogPrefetcherAllocate(xlogreader);

/*
  * Allocate two page buffers dedicated to WAL consistency checks.  We do
  * it this way, rather than just making static arrays, for two reasons:
  * (1) no need to waste the storage in most instantiations of the backend;
  * (2) a static char array isn't guaranteed to have any particular
  * alignment, whereas palloc() will provide MAXALIGN'd storage.
*/
replay_image_masked = (char *) palloc(BLCKSZ);
primary_image_masked = (char *) palloc(BLCKSZ);

/*
  * Read the backup_label file.  We want to run this part of the recovery
  * process after checking for signal files and after performing validation
  * of the recovery parameters.
*/
if (read_backup_label(&CheckPointLoc, &CheckPointTLI, &backupEndRequired,
        &backupFromStandby))
{
  List    *tablespaces = NIL;

  /*
   * Archive recovery was requested, and thanks to the backup label
   * file, we know how far we need to replay to reach consistency. Enter
   * archive recovery directly.
*/
  InArchiveRecovery = true;
  if (StandbyModeRequested)
   EnableStandbyMode();

  /*
   * Omitting backup_label when creating a new replica, PITR node etc.
   * unfortunately is a common cause of corruption.  Logging that
   * backup_label was used makes it a bit easier to exclude that as the
   * cause of observed corruption.
   *
   * Do so before we try to read the checkpoint record (which can fail),
   * as otherwise it can be hard to understand why a checkpoint other
   * than ControlFile->checkPoint is used.
*/
  ereport(LOG,
    (errmsg("starting backup recovery with redo LSN %X/%X, checkpoint LSN %X/%X, on timeline ID %u",
      LSN_FORMAT_ARGS(RedoStartLSN),
      LSN_FORMAT_ARGS(CheckPointLoc),
      CheckPointTLI)));

  /*
   * When a backup_label file is present, we want to roll forward from
   * the checkpoint it identifies, rather than using pg_control.
*/
  record = ReadCheckpointRecord(xlogprefetcher, CheckPointLoc,
           CheckPointTLI);
  if (record != NULL)
  {
   memcpy(&checkPoint, XLogRecGetData(xlogreader), sizeof(CheckPoint));
   wasShutdown = ((record->xl_info & ~XLR_INFO_MASK) == XLOG_CHECKPOINT_SHUTDOWN);
   ereport(DEBUG1,
     (errmsg_internal("checkpoint record is at %X/%X",
          LSN_FORMAT_ARGS(CheckPointLoc))));
   InRecovery = true; /* force recovery even if SHUTDOWNED */

   /*
    * Make sure that REDO location exists. This may not be the case
    * if there was a crash during an online backup, which left a
    * backup_label around that references a WAL segment that's
    * already been archived.
*/
   if (checkPoint.redo < CheckPointLoc)
   {
    XLogPrefetcherBeginRead(xlogprefetcher, checkPoint.redo);
    if (!ReadRecord(xlogprefetcher, LOG, false,
        checkPoint.ThisTimeLineID))
     ereport(FATAL,
       (errmsg("could not find redo location %X/%X referenced by checkpoint record at %X/%X",
         LSN_FORMAT_ARGS(checkPoint.redo), LSN_FORMAT_ARGS(CheckPointLoc)),
        errhint("If you are restoring from a backup, touch \"%s/recovery.signal\" or \"%s/standby.signal\" and add required recovery options.\n"
          "If you are not restoring from a backup, try removing the file \"%s/backup_label\".\n"
          "Be careful: removing \"%s/backup_label\" will result in a corrupt cluster if restoring from a backup.",
          DataDir, DataDir, DataDir, DataDir)));
   }
  }
  else
  {
   ereport(FATAL,
     (errmsg("could not locate required checkpoint record at %X/%X",
       LSN_FORMAT_ARGS(CheckPointLoc)),
      errhint("If you are restoring from a backup, touch \"%s/recovery.signal\" or \"%s/standby.signal\" and add required recovery options.\n"
        "If you are not restoring from a backup, try removing the file \"%s/backup_label\".\n"
        "Be careful: removing \"%s/backup_label\" will result in a corrupt cluster if restoring from a backup.",
        DataDir, DataDir, DataDir, DataDir)));
   wasShutdown = false; /* keep compiler quiet */
  }

  /* Read the tablespace_map file if present and create symlinks. */
  if (read_tablespace_map(&tablespaces))
  {
   ListCell   *lc;

   foreach(lc, tablespaces)
   {
    tablespaceinfo *ti = lfirst(lc);
    char    *linkloc;

    linkloc = psprintf("%s/%u", PG_TBLSPC_DIR, ti->oid);

    /*
     * Remove the existing symlink if any and Create the symlink
     * under PGDATA.
*/
    remove_tablespace_symlink(linkloc);

    if (symlink(ti->path, linkloc) < 0)
     ereport(ERROR,
       (errcode_for_file_access(),
        errmsg("could not create symbolic link \"%s\": %m",
         linkloc)));

    pfree(ti->path);
    pfree(ti);
   }

   /* tell the caller to delete it later */
   haveTblspcMap = true;
  }

  /* tell the caller to delete it later */
  haveBackupLabel = true;
}
else
{
  /* No backup_label file has been found if we are here. */

  /*
   * If tablespace_map file is present without backup_label file, there
   * is no use of such file.  There is no harm in retaining it, but it
   * is better to get rid of the map file so that we don't have any
   * redundant file in data directory and it will avoid any sort of
   * confusion.  It seems prudent though to just rename the file out of
   * the way rather than delete it completely, also we ignore any error
   * that occurs in rename operation as even if map file is present
   * without backup_label file, it is harmless.
*/
  if (stat(TABLESPACE_MAP, &st) == 0)
  {
   unlink(TABLESPACE_MAP_OLD);
   if (durable_rename(TABLESPACE_MAP, TABLESPACE_MAP_OLD, DEBUG1) == 0)
    ereport(LOG,
      (errmsg("ignoring file \"%s\" because no file \"%s\" exists",
        TABLESPACE_MAP, BACKUP_LABEL_FILE),
       errdetail("File \"%s\" was renamed to \"%s\".",
           TABLESPACE_MAP, TABLESPACE_MAP_OLD)));
   else
    ereport(LOG,
      (errmsg("ignoring file \"%s\" because no file \"%s\" exists",
        TABLESPACE_MAP, BACKUP_LABEL_FILE),
       errdetail("Could not rename file \"%s\" to \"%s\": %m.",
           TABLESPACE_MAP, TABLESPACE_MAP_OLD)));
  }

  /*
   * It's possible that archive recovery was requested, but we don't
   * know how far we need to replay the WAL before we reach consistency.
   * This can happen for example if a base backup is taken from a
   * running server using an atomic filesystem snapshot, without calling
   * pg_backup_start/stop. Or if you just kill a running primary server
   * and put it into archive recovery by creating a recovery signal
   * file.
   *
   * Our strategy in that case is to perform crash recovery first,
   * replaying all the WAL present in pg_wal, and only enter archive
   * recovery after that.
   *
   * But usually we already know how far we need to replay the WAL (up
   * to minRecoveryPoint, up to backupEndPoint, or until we see an
   * end-of-backup record), and we can enter archive recovery directly.
*/
  if (ArchiveRecoveryRequested &&
   (ControlFile->minRecoveryPoint != InvalidXLogRecPtr ||
    ControlFile->backupEndRequired ||
    ControlFile->backupEndPoint != InvalidXLogRecPtr ||
    ControlFile->state == DB_SHUTDOWNED))
  {
   InArchiveRecovery = true;
   if (StandbyModeRequested)
    EnableStandbyMode();
  }

  /*
   * For the same reason as when starting up with backup_label present,
   * emit a log message when we continue initializing from a base
   * backup.
*/
  if (!XLogRecPtrIsInvalid(ControlFile->backupStartPoint))
   ereport(LOG,
     (errmsg("restarting backup recovery with redo LSN %X/%X",
       LSN_FORMAT_ARGS(ControlFile->backupStartPoint))));

  /* Get the last valid checkpoint record. */
  CheckPointLoc = ControlFile->checkPoint;
  CheckPointTLI = ControlFile->checkPointCopy.ThisTimeLineID;
  RedoStartLSN = ControlFile->checkPointCopy.redo;
  RedoStartTLI = ControlFile->checkPointCopy.ThisTimeLineID;
  record = ReadCheckpointRecord(xlogprefetcher, CheckPointLoc,
           CheckPointTLI);
  if (record != NULL)
  {
   ereport(DEBUG1,
     (errmsg_internal("checkpoint record is at %X/%X",
          LSN_FORMAT_ARGS(CheckPointLoc))));
  }
  else
  {
   /*
    * We used to attempt to go back to a secondary checkpoint record
    * here, but only when not in standby mode. We now just fail if we
    * can't read the last checkpoint because this allows us to
    * simplify processing around checkpoints.
*/
   ereport(PANIC,
     (errmsg("could not locate a valid checkpoint record at %X/%X",
       LSN_FORMAT_ARGS(CheckPointLoc))));
  }
  memcpy(&checkPoint, XLogRecGetData(xlogreader), sizeof(CheckPoint));
  wasShutdown = ((record->xl_info & ~XLR_INFO_MASK) == XLOG_CHECKPOINT_SHUTDOWN);

  /* Make sure that REDO location exists. */
  if (checkPoint.redo < CheckPointLoc)
  {
   XLogPrefetcherBeginRead(xlogprefetcher, checkPoint.redo);
   if (!ReadRecord(xlogprefetcher, LOG, false, checkPoint.ThisTimeLineID))
    ereport(PANIC,
      errmsg("could not find redo location %X/%08X referenced by checkpoint record at %X/%08X",
          LSN_FORMAT_ARGS(checkPoint.redo), LSN_FORMAT_ARGS(CheckPointLoc)));
  }
}

if (ArchiveRecoveryRequested)
{
  if (StandbyModeRequested)
   ereport(LOG,
     (errmsg("entering standby mode")));
  else if (recoveryTarget == RECOVERY_TARGET_XID)
   ereport(LOG,
     (errmsg("starting point-in-time recovery to XID %u",
       recoveryTargetXid)));
  else if (recoveryTarget == RECOVERY_TARGET_TIME)
   ereport(LOG,
     (errmsg("starting point-in-time recovery to %s",
       timestamptz_to_str(recoveryTargetTime))));
  else if (recoveryTarget == RECOVERY_TARGET_NAME)
   ereport(LOG,
     (errmsg("starting point-in-time recovery to \"%s\"",
       recoveryTargetName)));
  else if (recoveryTarget == RECOVERY_TARGET_LSN)
   ereport(LOG,
     (errmsg("starting point-in-time recovery to WAL location (LSN) \"%X/%X\"",
       LSN_FORMAT_ARGS(recoveryTargetLSN))));
  else if (recoveryTarget == RECOVERY_TARGET_IMMEDIATE)
   ereport(LOG,
     (errmsg("starting point-in-time recovery to earliest consistent point")));
  else
   ereport(LOG,
     (errmsg("starting archive recovery")));
}

/*
  * If the location of the checkpoint record is not on the expected
  * timeline in the history of the requested timeline, we cannot proceed:
  * the backup is not part of the history of the requested timeline.
*/
Assert(expectedTLEs);  /* was initialized by reading checkpoint
* record */
if (tliOfPointInHistory(CheckPointLoc, expectedTLEs) !=
  CheckPointTLI)
{
  XLogRecPtr switchpoint;

  /*
   * tliSwitchPoint will throw an error if the checkpoint's timeline is
   * not in expectedTLEs at all.
*/
  switchpoint = tliSwitchPoint(CheckPointTLI, expectedTLEs, NULL);
  ereport(FATAL,
    (errmsg("requested timeline %u is not a child of this server's history",
      recoveryTargetTLI),
  /* translator: %s is a backup_label file or a pg_control file */
     errdetail("Latest checkpoint in file \"%s\" is at %X/%X on timeline %u, but in the history of the requested timeline, the server forked off from that timeline at %X/%X.",
         haveBackupLabel ? "backup_label" : "pg_control",
         LSN_FORMAT_ARGS(CheckPointLoc),
         CheckPointTLI,
         LSN_FORMAT_ARGS(switchpoint))));
}

/*
  * The min recovery point should be part of the requested timeline's
  * history, too.
*/
if (!XLogRecPtrIsInvalid(ControlFile->minRecoveryPoint) &&
  tliOfPointInHistory(ControlFile->minRecoveryPoint - 1, expectedTLEs) !=
  ControlFile->minRecoveryPointTLI)
  ereport(FATAL,
    (errmsg("requested timeline %u does not contain minimum recovery point %X/%X on timeline %u",
      recoveryTargetTLI,
      LSN_FORMAT_ARGS(ControlFile->minRecoveryPoint),
      ControlFile->minRecoveryPointTLI)));

ereport(DEBUG1,
   (errmsg_internal("redo record is at %X/%X; shutdown %s",
        LSN_FORMAT_ARGS(checkPoint.redo),
        wasShutdown ? "true" : "false")));
ereport(DEBUG1,
   (errmsg_internal("next transaction ID: " UINT64_FORMAT "; next OID: %u",
        U64FromFullTransactionId(checkPoint.nextXid),
        checkPoint.nextOid)));
ereport(DEBUG1,
   (errmsg_internal("next MultiXactId: %u; next MultiXactOffset: %u",
        checkPoint.nextMulti, checkPoint.nextMultiOffset)));
ereport(DEBUG1,
   (errmsg_internal("oldest unfrozen transaction ID: %u, in database %u",
        checkPoint.oldestXid, checkPoint.oldestXidDB)));
ereport(DEBUG1,
   (errmsg_internal("oldest MultiXactId: %u, in database %u",
        checkPoint.oldestMulti, checkPoint.oldestMultiDB)));
ereport(DEBUG1,
   (errmsg_internal("commit timestamp Xid oldest/newest: %u/%u",
        checkPoint.oldestCommitTsXid,
        checkPoint.newestCommitTsXid)));
if (!TransactionIdIsNormal(XidFromFullTransactionId(checkPoint.nextXid)))
  ereport(PANIC,
    (errmsg("invalid next transaction ID")));

/* sanity check */
if (checkPoint.redo > CheckPointLoc)
  ereport(PANIC,
    (errmsg("invalid redo in checkpoint record")));

/*
  * Check whether we need to force recovery from WAL.  If it appears to
  * have been a clean shutdown and we did not have a recovery signal file,
  * then assume no recovery needed.
*/
if (checkPoint.redo < CheckPointLoc)
{
  if (wasShutdown)
   ereport(PANIC,
     (errmsg("invalid redo record in shutdown checkpoint")));
  InRecovery = true;
}
else if (ControlFile->state != DB_SHUTDOWNED)
  InRecovery = true;
else if (ArchiveRecoveryRequested)
{
  /* force recovery due to presence of recovery signal file */
  InRecovery = true;
}

/*
  * If recovery is needed, update our in-memory copy of pg_control to show
  * that we are recovering and to show the selected checkpoint as the place
  * we are starting from. We also mark pg_control with any minimum recovery
  * stop point obtained from a backup history file.
  *
  * We don't write the changes to disk yet, though. Only do that after
  * initializing various subsystems.
*/
if (InRecovery)
{
  if (InArchiveRecovery)
  {
   ControlFile->state = DB_IN_ARCHIVE_RECOVERY;
  }
  else
  {
   ereport(LOG,
     (errmsg("database system was not properly shut down; "
       "automatic recovery in progress")));
   if (recoveryTargetTLI > ControlFile->checkPointCopy.ThisTimeLineID)
    ereport(LOG,
      (errmsg("crash recovery starts in timeline %u "
        "and has target timeline %u",
        ControlFile->checkPointCopy.ThisTimeLineID,
        recoveryTargetTLI)));
   ControlFile->state = DB_IN_CRASH_RECOVERY;
  }
  ControlFile->checkPoint = CheckPointLoc;
  ControlFile->checkPointCopy = checkPoint;
  if (InArchiveRecovery)
  {
   /* initialize minRecoveryPoint if not set yet */
   if (ControlFile->minRecoveryPoint < checkPoint.redo)
   {
    ControlFile->minRecoveryPoint = checkPoint.redo;
    ControlFile->minRecoveryPointTLI = checkPoint.ThisTimeLineID;
   }
  }

  /*
   * Set backupStartPoint if we're starting recovery from a base backup.
   *
   * Also set backupEndPoint and use minRecoveryPoint as the backup end
   * location if we're starting recovery from a base backup which was
   * taken from a standby. In this case, the database system status in
   * pg_control must indicate that the database was already in recovery.
   * Usually that will be DB_IN_ARCHIVE_RECOVERY but also can be
   * DB_SHUTDOWNED_IN_RECOVERY if recovery previously was interrupted
   * before reaching this point; e.g. because restore_command or
   * primary_conninfo were faulty.
   *
   * Any other state indicates that the backup somehow became corrupted
   * and we can't sensibly continue with recovery.
*/
  if (haveBackupLabel)
  {
   ControlFile->backupStartPoint = checkPoint.redo;
   ControlFile->backupEndRequired = backupEndRequired;

   if (backupFromStandby)
   {
    if (dbstate_at_startup != DB_IN_ARCHIVE_RECOVERY &&
     dbstate_at_startup != DB_SHUTDOWNED_IN_RECOVERY)
     ereport(FATAL,
       (errmsg("backup_label contains data inconsistent with control file"),
        errhint("This means that the backup is corrupted and you will "
          "have to use another backup for recovery.")));
    ControlFile->backupEndPoint = ControlFile->minRecoveryPoint;
   }
  }
}

/* remember these, so that we know when we have reached consistency */
backupStartPoint = ControlFile->backupStartPoint;
backupEndRequired = ControlFile->backupEndRequired;
backupEndPoint = ControlFile->backupEndPoint;
if (InArchiveRecovery)
{
  minRecoveryPoint = ControlFile->minRecoveryPoint;
  minRecoveryPointTLI = ControlFile->minRecoveryPointTLI;
}
else
{
  minRecoveryPoint = InvalidXLogRecPtr;
  minRecoveryPointTLI = 0;
}

/*
  * Start recovery assuming that the final record isn't lost.
*/
abortedRecPtr = InvalidXLogRecPtr;
missingContrecPtr = InvalidXLogRecPtr;

*wasShutdown_ptr = wasShutdown;
*haveBackupLabel_ptr = haveBackupLabel;
*haveTblspcMap_ptr = haveTblspcMap;
}

/*
* See if there are any recovery signal files and if so, set state for
* recovery.
*
* See if there is a recovery command file (recovery.conf), and if so
* throw an ERROR since as of PG12 we no longer recognize that.
*/
static void
readRecoverySignalFile(void)
{
struct stat stat_buf;

if (IsBootstrapProcessingMode())
  return;

/*
  * Check for old recovery API file: recovery.conf
*/
if (stat(RECOVERY_COMMAND_FILE, &stat_buf) == 0)
  ereport(FATAL,
    (errcode_for_file_access(),
     errmsg("using recovery command file \"%s\" is not supported",
      RECOVERY_COMMAND_FILE)));

/*
  * Remove unused .done file, if present. Ignore if absent.
*/
unlink(RECOVERY_COMMAND_DONE);

/*
  * Check for recovery signal files and if found, fsync them since they
  * represent server state information.  We don't sweat too much about the
  * possibility of fsync failure, however.
  *
  * If present, standby signal file takes precedence. If neither is present
  * then we won't enter archive recovery.
*/
if (stat(STANDBY_SIGNAL_FILE, &stat_buf) == 0)
{
  int   fd;

  fd = BasicOpenFilePerm(STANDBY_SIGNAL_FILE, O_RDWR | PG_BINARY,
          S_IRUSR | S_IWUSR);
  if (fd >= 0)
  {
   (void) pg_fsync(fd);
   close(fd);
  }
  standby_signal_file_found = true;
}
else if (stat(RECOVERY_SIGNAL_FILE, &stat_buf) == 0)
{
  int   fd;

  fd = BasicOpenFilePerm(RECOVERY_SIGNAL_FILE, O_RDWR | PG_BINARY,
          S_IRUSR | S_IWUSR);
  if (fd >= 0)
  {
   (void) pg_fsync(fd);
   close(fd);
  }
  recovery_signal_file_found = true;
}

StandbyModeRequested = false;
ArchiveRecoveryRequested = false;
if (standby_signal_file_found)
{
  StandbyModeRequested = true;
  ArchiveRecoveryRequested = true;
}
else if (recovery_signal_file_found)
{
  StandbyModeRequested = false;
  ArchiveRecoveryRequested = true;
}
else
  return;

/*
  * We don't support standby mode in standalone backends; that requires
  * other processes such as the WAL receiver to be alive.
*/
if (StandbyModeRequested && !IsUnderPostmaster)
  ereport(FATAL,
    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
     errmsg("standby mode is not supported by single-user servers")));
}

static void
validateRecoveryParameters(void)
{
if (!ArchiveRecoveryRequested)
  return;

/*
  * Check for compulsory parameters
*/
if (StandbyModeRequested)
{
  if ((PrimaryConnInfo == NULL || strcmp(PrimaryConnInfo, "") == 0) &&
   (recoveryRestoreCommand == NULL || strcmp(recoveryRestoreCommand, "") == 0))
   ereport(WARNING,
     (errmsg("specified neither \"primary_conninfo\" nor \"restore_command\""),
      errhint("The database server will regularly poll the pg_wal subdirectory to check for files placed there.")));
}
else
{
  if (recoveryRestoreCommand == NULL ||
   strcmp(recoveryRestoreCommand, "") == 0)
   ereport(FATAL,
     (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
      errmsg("must specify \"restore_command\" when standby mode is not enabled")));
}

/*
  * Override any inconsistent requests. Note that this is a change of
  * behaviour in 9.5; prior to this we simply ignored a request to pause if
  * hot_standby = off, which was surprising behaviour.
*/
if (recoveryTargetAction == RECOVERY_TARGET_ACTION_PAUSE &&
  !EnableHotStandby)
  recoveryTargetAction = RECOVERY_TARGET_ACTION_SHUTDOWN;

/*
  * Final parsing of recovery_target_time string; see also
  * check_recovery_target_time().
*/
if (recoveryTarget == RECOVERY_TARGET_TIME)
{
  recoveryTargetTime = DatumGetTimestampTz(DirectFunctionCall3(timestamptz_in,
                  CStringGetDatum(recovery_target_time_string),
                  ObjectIdGetDatum(InvalidOid),
                  Int32GetDatum(-1)));
}

/*
  * If user specified recovery_target_timeline, validate it or compute the
  * "latest" value.  We can't do this until after we've gotten the restore
  * command and set InArchiveRecovery, because we need to fetch timeline
  * history files from the archive.
*/
if (recoveryTargetTimeLineGoal == RECOVERY_TARGET_TIMELINE_NUMERIC)
{
  TimeLineID rtli = recoveryTargetTLIRequested;

  /* Timeline 1 does not have a history file, all else should */
  if (rtli != 1 && !existsTimeLineHistory(rtli))
   ereport(FATAL,
     (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
      errmsg("recovery target timeline %u does not exist",
       rtli)));
  recoveryTargetTLI = rtli;
}
else if (recoveryTargetTimeLineGoal == RECOVERY_TARGET_TIMELINE_LATEST)
{
  /* We start the "latest" search from pg_control's timeline */
  recoveryTargetTLI = findNewestTimeLine(recoveryTargetTLI);
}
else
{
  /*
   * else we just use the recoveryTargetTLI as already read from
   * ControlFile
*/
  Assert(recoveryTargetTimeLineGoal == RECOVERY_TARGET_TIMELINE_CONTROLFILE);
}
}

/*
* read_backup_label: check to see if a backup_label file is present
*
* If we see a backup_label during recovery, we assume that we are recovering
* from a backup dump file, and we therefore roll forward from the checkpoint
* identified by the label file, NOT what pg_control says.  This avoids the
* problem that pg_control might have been archived one or more checkpoints
* later than the start of the dump, and so if we rely on it as the start
* point, we will fail to restore a consistent database state.
*
* Returns true if a backup_label was found (and fills the checkpoint
* location and TLI into *checkPointLoc and *backupLabelTLI, respectively);
* returns false if not. If this backup_label came from a streamed backup,
* *backupEndRequired is set to true. If this backup_label was created during
* recovery, *backupFromStandby is set to true.
*
* Also sets the global variables RedoStartLSN and RedoStartTLI with the LSN
* and TLI read from the backup file.
*/
static bool
read_backup_label(XLogRecPtr *checkPointLoc, TimeLineID *backupLabelTLI,
      bool *backupEndRequired, bool *backupFromStandby)
{
char  startxlogfilename[MAXFNAMELEN];
TimeLineID tli_from_walseg,
    tli_from_file;
FILE    *lfp;
char  ch;
char  backuptype[20];
char  backupfrom[20];
char  backuplabel[MAXPGPATH];
char  backuptime[128];
uint32  hi,
    lo;

/* suppress possible uninitialized-variable warnings */
*checkPointLoc = InvalidXLogRecPtr;
*backupLabelTLI = 0;
*backupEndRequired = false;
*backupFromStandby = false;

/*
  * See if label file is present
*/
lfp = AllocateFile(BACKUP_LABEL_FILE, "r");
if (!lfp)
{
  if (errno != ENOENT)
   ereport(FATAL,
     (errcode_for_file_access(),
      errmsg("could not read file \"%s\": %m",
       BACKUP_LABEL_FILE)));
  return false;   /* it's not there, all is fine */
}

/*
  * Read and parse the START WAL LOCATION and CHECKPOINT lines (this code
  * is pretty crude, but we are not expecting any variability in the file
  * format).
*/
if (fscanf(lfp, "START WAL LOCATION: %X/%X (file %08X%16s)%c",
      &hi, &lo, &tli_from_walseg, startxlogfilename, &ch) != 5 || ch != '\n')
  ereport(FATAL,
    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
     errmsg("invalid data in file \"%s\"", BACKUP_LABEL_FILE)));
RedoStartLSN = ((uint64) hi) << 32 | lo;
RedoStartTLI = tli_from_walseg;
if (fscanf(lfp, "CHECKPOINT LOCATION: %X/%X%c",
      &hi, &lo, &ch) != 3 || ch != '\n')
  ereport(FATAL,
    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
     errmsg("invalid data in file \"%s\"", BACKUP_LABEL_FILE)));
*checkPointLoc = ((uint64) hi) << 32 | lo;
*backupLabelTLI = tli_from_walseg;

/*
  * BACKUP METHOD lets us know if this was a typical backup ("streamed",
  * which could mean either pg_basebackup or the pg_backup_start/stop
  * method was used) or if this label came from somewhere else (the only
  * other option today being from pg_rewind).  If this was a streamed
  * backup then we know that we need to play through until we get to the
  * end of the WAL which was generated during the backup (at which point we
  * will have reached consistency and backupEndRequired will be reset to be
  * false).
*/
if (fscanf(lfp, "BACKUP METHOD: %19s\n", backuptype) == 1)
{
  if (strcmp(backuptype, "streamed") == 0)
   *backupEndRequired = true;
}

/*
  * BACKUP FROM lets us know if this was from a primary or a standby.  If
  * it was from a standby, we'll double-check that the control file state
  * matches that of a standby.
*/
if (fscanf(lfp, "BACKUP FROM: %19s\n", backupfrom) == 1)
{
  if (strcmp(backupfrom, "standby") == 0)
   *backupFromStandby = true;
}

/*
  * Parse START TIME and LABEL. Those are not mandatory fields for recovery
  * but checking for their presence is useful for debugging and the next
  * sanity checks. Cope also with the fact that the result buffers have a
  * pre-allocated size, hence if the backup_label file has been generated
  * with strings longer than the maximum assumed here an incorrect parsing
  * happens. That's fine as only minor consistency checks are done
  * afterwards.
*/
if (fscanf(lfp, "START TIME: %127[^\n]\n", backuptime) == 1)
  ereport(DEBUG1,
    (errmsg_internal("backup time %s in file \"%s\"",
         backuptime, BACKUP_LABEL_FILE)));

if (fscanf(lfp, "LABEL: %1023[^\n]\n", backuplabel) == 1)
  ereport(DEBUG1,
    (errmsg_internal("backup label %s in file \"%s\"",
         backuplabel, BACKUP_LABEL_FILE)));

/*
  * START TIMELINE is new as of 11. Its parsing is not mandatory, still use
  * it as a sanity check if present.
*/
if (fscanf(lfp, "START TIMELINE: %u\n", &tli_from_file) == 1)
{
  if (tli_from_walseg != tli_from_file)
   ereport(FATAL,
     (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
      errmsg("invalid data in file \"%s\"", BACKUP_LABEL_FILE),
      errdetail("Timeline ID parsed is %u, but expected %u.",
          tli_from_file, tli_from_walseg)));

  ereport(DEBUG1,
    (errmsg_internal("backup timeline %u in file \"%s\"",
         tli_from_file, BACKUP_LABEL_FILE)));
}

if (fscanf(lfp, "INCREMENTAL FROM LSN: %X/%X\n", &hi, &lo) > 0)
  ereport(FATAL,
    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
     errmsg("this is an incremental backup, not a data directory"),
     errhint("Use pg_combinebackup to reconstruct a valid data directory.")));

if (ferror(lfp) || FreeFile(lfp))
  ereport(FATAL,
    (errcode_for_file_access(),
     errmsg("could not read file \"%s\": %m",
      BACKUP_LABEL_FILE)));

return true;
}

/*
* read_tablespace_map: check to see if a tablespace_map file is present
*
* If we see a tablespace_map file during recovery, we assume that we are
* recovering from a backup dump file, and we therefore need to create symlinks
* as per the information present in tablespace_map file.
*
* Returns true if a tablespace_map file was found (and fills *tablespaces
* with a tablespaceinfo struct for each tablespace listed in the file);
* returns false if not.
*/
static bool
read_tablespace_map(List **tablespaces)
{
tablespaceinfo *ti;
FILE    *lfp;
char  str[MAXPGPATH];
int   ch,
    i,
    n;
bool  was_backslash;

/*
  * See if tablespace_map file is present
*/
lfp = AllocateFile(TABLESPACE_MAP, "r");
if (!lfp)
{
  if (errno != ENOENT)
   ereport(FATAL,
     (errcode_for_file_access(),
      errmsg("could not read file \"%s\": %m",
       TABLESPACE_MAP)));
  return false;   /* it's not there, all is fine */
}

/*
  * Read and parse the link name and path lines from tablespace_map file
  * (this code is pretty crude, but we are not expecting any variability in
  * the file format).  De-escape any backslashes that were inserted.
*/
i = 0;
was_backslash = false;
while ((ch = fgetc(lfp)) != EOF)
{
  if (!was_backslash && (ch == '\n' || ch == '\r'))
  {
   char    *endp;

   if (i == 0)
    continue;  /* \r immediately followed by \n */

   /*
    * The de-escaped line should contain an OID followed by exactly
    * one space followed by a path.  The path might start with
    * spaces, so don't be too liberal about parsing.
*/
   str[i] = '\0';
   n = 0;
   while (str[n] && str[n] != ' ')
    n++;
   if (n < 1 || n >= i - 1)
    ereport(FATAL,
      (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
       errmsg("invalid data in file \"%s\"", TABLESPACE_MAP)));
   str[n++] = '\0';

   ti = palloc0(sizeof(tablespaceinfo));
   errno = 0;
   ti->oid = strtoul(str, &endp, 10);
   if (*endp != '\0' || errno == EINVAL || errno == ERANGE)
    ereport(FATAL,
      (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
       errmsg("invalid data in file \"%s\"", TABLESPACE_MAP)));
   ti->path = pstrdup(str + n);
   *tablespaces = lappend(*tablespaces, ti);

   i = 0;
   continue;
  }
  else if (!was_backslash && ch == '\\')
   was_backslash = true;
  else
  {
   if (i < sizeof(str) - 1)
    str[i++] = ch;
   was_backslash = false;
  }
}

if (i != 0 || was_backslash) /* last line not terminated? */
  ereport(FATAL,
    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
     errmsg("invalid data in file \"%s\"", TABLESPACE_MAP)));

if (ferror(lfp) || FreeFile(lfp))
  ereport(FATAL,
    (errcode_for_file_access(),
     errmsg("could not read file \"%s\": %m",
      TABLESPACE_MAP)));

return true;
}

/*
* Finish WAL recovery.
*
* This does not close the 'xlogreader' yet, because in some cases the caller
* still wants to re-read the last checkpoint record by calling
* ReadCheckpointRecord().
*
* Returns the position of the last valid or applied record, after which new
* WAL should be appended, information about why recovery was ended, and some
* other things. See the EndOfWalRecoveryInfo struct for details.
*/
EndOfWalRecoveryInfo *
FinishWalRecovery(void)
{
EndOfWalRecoveryInfo *result = palloc(sizeof(EndOfWalRecoveryInfo));
XLogRecPtr lastRec;
TimeLineID lastRecTLI;
XLogRecPtr endOfLog;

/*
  * Kill WAL receiver, if it's still running, before we continue to write
  * the startup checkpoint and aborted-contrecord records. It will trump
  * over these records and subsequent ones if it's still alive when we
  * start writing WAL.
*/
XLogShutdownWalRcv();

/*
  * Shutdown the slot sync worker to drop any temporary slots acquired by
  * it and to prevent it from keep trying to fetch the failover slots.
  *
  * We do not update the 'synced' column in 'pg_replication_slots' system
  * view from true to false here, as any failed update could leave 'synced'
  * column false for some slots. This could cause issues during slot sync
  * after restarting the server as a standby. While updating the 'synced'
  * column after switching to the new timeline is an option, it does not
  * simplify the handling for the 'synced' column. Therefore, we retain the
  * 'synced' column as true after promotion as it may provide useful
  * information about the slot origin.
*/
ShutDownSlotSync();

/*
  * We are now done reading the xlog from stream. Turn off streaming
  * recovery to force fetching the files (which would be required at end of
  * recovery, e.g., timeline history file) from archive or pg_wal.
  *
  * Note that standby mode must be turned off after killing WAL receiver,
  * i.e., calling XLogShutdownWalRcv().
*/
Assert(!WalRcvStreaming());
StandbyMode = false;

/*
  * Determine where to start writing WAL next.
  *
  * Re-fetch the last valid or last applied record, so we can identify the
  * exact endpoint of what we consider the valid portion of WAL.  There may
  * be an incomplete continuation record after that, in which case
  * 'abortedRecPtr' and 'missingContrecPtr' are set and the caller will
  * write a special OVERWRITE_CONTRECORD message to mark that the rest of
  * it is intentionally missing.  See CreateOverwriteContrecordRecord().
  *
  * An important side-effect of this is to load the last page into
  * xlogreader. The caller uses it to initialize the WAL for writing.
*/
if (!InRecovery)
{
  lastRec = CheckPointLoc;
  lastRecTLI = CheckPointTLI;
}
else
{
  lastRec = XLogRecoveryCtl->lastReplayedReadRecPtr;
  lastRecTLI = XLogRecoveryCtl->lastReplayedTLI;
}
XLogPrefetcherBeginRead(xlogprefetcher, lastRec);
(void) ReadRecord(xlogprefetcher, PANIC, false, lastRecTLI);
endOfLog = xlogreader->EndRecPtr;

/*
  * Remember the TLI in the filename of the XLOG segment containing the
  * end-of-log.  It could be different from the timeline that endOfLog
  * nominally belongs to, if there was a timeline switch in that segment,
  * and we were reading the old WAL from a segment belonging to a higher
  * timeline.
*/
result->endOfLogTLI = xlogreader->seg.ws_tli;

if (ArchiveRecoveryRequested)
{
  /*
   * We are no longer in archive recovery state.
   *
   * We are now done reading the old WAL.  Turn off archive fetching if
   * it was active.
*/
  Assert(InArchiveRecovery);
  InArchiveRecovery = false;

  /*
   * If the ending log segment is still open, close it (to avoid
   * problems on Windows with trying to rename or delete an open file).
*/
  if (readFile >= 0)
  {
   close(readFile);
   readFile = -1;
  }
}

/*
  * Copy the last partial block to the caller, for initializing the WAL
  * buffer for appending new WAL.
*/
if (endOfLog % XLOG_BLCKSZ != 0)
{
  char    *page;
  int   len;
  XLogRecPtr pageBeginPtr;

  pageBeginPtr = endOfLog - (endOfLog % XLOG_BLCKSZ);
  Assert(readOff == XLogSegmentOffset(pageBeginPtr, wal_segment_size));

  /* Copy the valid part of the last block */
  len = endOfLog % XLOG_BLCKSZ;
  page = palloc(len);
  memcpy(page, xlogreader->readBuf, len);

  result->lastPageBeginPtr = pageBeginPtr;
  result->lastPage = page;
}
else
{
  /* There is no partial block to copy. */
  result->lastPageBeginPtr = endOfLog;
  result->lastPage = NULL;
}

/*
  * Create a comment for the history file to explain why and where timeline
  * changed.
*/
result->recoveryStopReason = getRecoveryStopReason();

result->lastRec = lastRec;
result->lastRecTLI = lastRecTLI;
result->endOfLog = endOfLog;

result->abortedRecPtr = abortedRecPtr;
result->missingContrecPtr = missingContrecPtr;

result->standby_signal_file_found = standby_signal_file_found;
result->recovery_signal_file_found = recovery_signal_file_found;

return result;
}

/*
* Clean up the WAL reader and leftovers from restoring WAL from archive
*/
void
ShutdownWalRecovery(void)
{
char  recoveryPath[MAXPGPATH];

/* Final update of pg_stat_recovery_prefetch. */
XLogPrefetcherComputeStats(xlogprefetcher);

/* Shut down xlogreader */
if (readFile >= 0)
{
  close(readFile);
  readFile = -1;
}
XLogReaderFree(xlogreader);
XLogPrefetcherFree(xlogprefetcher);

if (ArchiveRecoveryRequested)
{
  /*
   * Since there might be a partial WAL segment named RECOVERYXLOG, get
   * rid of it.
*/
  snprintf(recoveryPath, MAXPGPATH, XLOGDIR "/RECOVERYXLOG");
  unlink(recoveryPath); /* ignore any error */

  /* Get rid of any remaining recovered timeline-history file, too */
  snprintf(recoveryPath, MAXPGPATH, XLOGDIR "/RECOVERYHISTORY");
  unlink(recoveryPath); /* ignore any error */
}

/*
  * We don't need the latch anymore. It's not strictly necessary to disown
  * it, but let's do it for the sake of tidiness.
*/
if (ArchiveRecoveryRequested)
  DisownLatch(&XLogRecoveryCtl->recoveryWakeupLatch);
}

/*
* Perform WAL recovery.
*
* If the system was shut down cleanly, this is never called.
*/
void
PerformWalRecovery(void)
{
XLogRecord *record;
bool  reachedRecoveryTarget = false;
TimeLineID replayTLI;

/*
  * Initialize shared variables for tracking progress of WAL replay, as if
  * we had just replayed the record before the REDO location (or the
  * checkpoint record itself, if it's a shutdown checkpoint).
*/
SpinLockAcquire(&XLogRecoveryCtl->info_lck);
if (RedoStartLSN < CheckPointLoc)
{
  XLogRecoveryCtl->lastReplayedReadRecPtr = InvalidXLogRecPtr;
  XLogRecoveryCtl->lastReplayedEndRecPtr = RedoStartLSN;
  XLogRecoveryCtl->lastReplayedTLI = RedoStartTLI;
}
else
{
  XLogRecoveryCtl->lastReplayedReadRecPtr = xlogreader->ReadRecPtr;
  XLogRecoveryCtl->lastReplayedEndRecPtr = xlogreader->EndRecPtr;
  XLogRecoveryCtl->lastReplayedTLI = CheckPointTLI;
}
XLogRecoveryCtl->replayEndRecPtr = XLogRecoveryCtl->lastReplayedEndRecPtr;
XLogRecoveryCtl->replayEndTLI = XLogRecoveryCtl->lastReplayedTLI;
XLogRecoveryCtl->recoveryLastXTime = 0;
XLogRecoveryCtl->currentChunkStartTime = 0;
XLogRecoveryCtl->recoveryPauseState = RECOVERY_NOT_PAUSED;
SpinLockRelease(&XLogRecoveryCtl->info_lck);

/* Also ensure XLogReceiptTime has a sane value */
XLogReceiptTime = GetCurrentTimestamp();

/*
  * Let postmaster know we've started redo now, so that it can launch the
  * archiver if necessary.
*/
if (IsUnderPostmaster)
  SendPostmasterSignal(PMSIGNAL_RECOVERY_STARTED);

/*
  * Allow read-only connections immediately if we're consistent already.
*/
CheckRecoveryConsistency();

/*
  * Find the first record that logically follows the checkpoint --- it
  * might physically precede it, though.
*/
if (RedoStartLSN < CheckPointLoc)
{
  /* back up to find the record */
  replayTLI = RedoStartTLI;
  XLogPrefetcherBeginRead(xlogprefetcher, RedoStartLSN);
  record = ReadRecord(xlogprefetcher, PANIC, false, replayTLI);

  /*
   * If a checkpoint record's redo pointer points back to an earlier
   * LSN, the record at that LSN should be an XLOG_CHECKPOINT_REDO
   * record.
*/
  if (record->xl_rmid != RM_XLOG_ID ||
   (record->xl_info & ~XLR_INFO_MASK) != XLOG_CHECKPOINT_REDO)
   ereport(FATAL,
     (errmsg("unexpected record type found at redo point %X/%X",
       LSN_FORMAT_ARGS(xlogreader->ReadRecPtr))));
}
else
{
  /* just have to read next record after CheckPoint */
  Assert(xlogreader->ReadRecPtr == CheckPointLoc);
  replayTLI = CheckPointTLI;
  record = ReadRecord(xlogprefetcher, LOG, false, replayTLI);
}

if (record != NULL)
{
  TimestampTz xtime;
  PGRUsage ru0;

  pg_rusage_init(&ru0);

  InRedo = true;

  RmgrStartup();

  ereport(LOG,
    (errmsg("redo starts at %X/%X",
      LSN_FORMAT_ARGS(xlogreader->ReadRecPtr))));

  /* Prepare to report progress of the redo phase. */
  if (!StandbyMode)
   begin_startup_progress_phase();

  /*
   * main redo apply loop
*/
  do
  {
   if (!StandbyMode)
    ereport_startup_progress("redo in progress, elapsed time: %ld.%02d s, current LSN: %X/%X",
           LSN_FORMAT_ARGS(xlogreader->ReadRecPtr));

#ifdef WAL_DEBUG
   if (XLOG_DEBUG)
   {
    StringInfoData buf;

    initStringInfo(&buf);
    appendStringInfo(&buf, "REDO @ %X/%X; LSN %X/%X: ",
         LSN_FORMAT_ARGS(xlogreader->ReadRecPtr),
         LSN_FORMAT_ARGS(xlogreader->EndRecPtr));
    xlog_outrec(&buf, xlogreader);
    appendStringInfoString(&buf, " - ");
    xlog_outdesc(&buf, xlogreader);
    elog(LOG, "%s", buf.data);
    pfree(buf.data);
   }
#endif

   /* Handle interrupt signals of startup process */
   ProcessStartupProcInterrupts();

   /*
    * Pause WAL replay, if requested by a hot-standby session via
    * SetRecoveryPause().
    *
    * Note that we intentionally don't take the info_lck spinlock
    * here.  We might therefore read a slightly stale value of the
    * recoveryPause flag, but it can't be very stale (no worse than
    * the last spinlock we did acquire).  Since a pause request is a
    * pretty asynchronous thing anyway, possibly responding to it one
    * WAL record later than we otherwise would is a minor issue, so
    * it doesn't seem worth adding another spinlock cycle to prevent
    * that.
*/
   if (((volatile XLogRecoveryCtlData *) XLogRecoveryCtl)->recoveryPauseState !=
    RECOVERY_NOT_PAUSED)
    recoveryPausesHere(false);

   /*
    * Have we reached our recovery target?
*/
   if (recoveryStopsBefore(xlogreader))
   {
    reachedRecoveryTarget = true;
    break;
   }

   /*
    * If we've been asked to lag the primary, wait on latch until
    * enough time has passed.
*/
   if (recoveryApplyDelay(xlogreader))
   {
    /*
     * We test for paused recovery again here. If user sets
     * delayed apply, it may be because they expect to pause
     * recovery in case of problems, so we must test again here
     * otherwise pausing during the delay-wait wouldn't work.
*/
    if (((volatile XLogRecoveryCtlData *) XLogRecoveryCtl)->recoveryPauseState !=
     RECOVERY_NOT_PAUSED)
     recoveryPausesHere(false);
   }

   /*
    * Apply the record
*/
   ApplyWalRecord(xlogreader, record, &replayTLI);

   /* Exit loop if we reached inclusive recovery target */
   if (recoveryStopsAfter(xlogreader))
   {
    reachedRecoveryTarget = true;
    break;
   }

   /* Else, try to fetch the next WAL record */
   record = ReadRecord(xlogprefetcher, LOG, false, replayTLI);
  } while (record != NULL);

  /*
   * end of main redo apply loop
*/

  if (reachedRecoveryTarget)
  {
   if (!reachedConsistency)
    ereport(FATAL,
      (errmsg("requested recovery stop point is before consistent recovery point")));

   /*
    * This is the last point where we can restart recovery with a new
    * recovery target, if we shutdown and begin again. After this,
    * Resource Managers may choose to do permanent corrective actions
    * at end of recovery.
*/
   switch (recoveryTargetAction)
   {
    case RECOVERY_TARGET_ACTION_SHUTDOWN:

     /*
      * exit with special return code to request shutdown of
      * postmaster.  Log messages issued from postmaster.
*/
     proc_exit(3);

    case RECOVERY_TARGET_ACTION_PAUSE:
     SetRecoveryPause(true);
     recoveryPausesHere(true);

     /* drop into promote */

    case RECOVERY_TARGET_ACTION_PROMOTE:
     break;
   }
  }

  RmgrCleanup();

  ereport(LOG,
    (errmsg("redo done at %X/%X system usage: %s",
      LSN_FORMAT_ARGS(xlogreader->ReadRecPtr),
      pg_rusage_show(&ru0))));
  xtime = GetLatestXTime();
  if (xtime)
   ereport(LOG,
     (errmsg("last completed transaction was at log time %s",
       timestamptz_to_str(xtime))));

  InRedo = false;
}
else
{
  /* there are no WAL records following the checkpoint */
  ereport(LOG,
    (errmsg("redo is not required")));
}

/*
  * This check is intentionally after the above log messages that indicate
  * how far recovery went.
*/
if (ArchiveRecoveryRequested &&
  recoveryTarget != RECOVERY_TARGET_UNSET &&
  !reachedRecoveryTarget)
  ereport(FATAL,
    (errcode(ERRCODE_CONFIG_FILE_ERROR),
     errmsg("recovery ended before configured recovery target was reached")));
}

/*
* Subroutine of PerformWalRecovery, to apply one WAL record.
*/
static void
ApplyWalRecord(XLogReaderState *xlogreader, XLogRecord *record, TimeLineID *replayTLI)
{
ErrorContextCallback errcallback;
bool  switchedTLI = false;

/* Setup error traceback support for ereport() */
errcallback.callback = rm_redo_error_callback;
errcallback.arg = xlogreader;
errcallback.previous = error_context_stack;
error_context_stack = &errcallback;

/*
  * TransamVariables->nextXid must be beyond record's xid.
*/
AdvanceNextFullTransactionIdPastXid(record->xl_xid);

/*
  * Before replaying this record, check if this record causes the current
  * timeline to change. The record is already considered to be part of the
  * new timeline, so we update replayTLI before replaying it. That's
  * important so that replayEndTLI, which is recorded as the minimum
  * recovery point's TLI if recovery stops after this record, is set
  * correctly.
*/
if (record->xl_rmid == RM_XLOG_ID)
{
  TimeLineID newReplayTLI = *replayTLI;
  TimeLineID prevReplayTLI = *replayTLI;
  uint8  info = record->xl_info & ~XLR_INFO_MASK;

  if (info == XLOG_CHECKPOINT_SHUTDOWN)
  {
   CheckPoint checkPoint;

   memcpy(&checkPoint, XLogRecGetData(xlogreader), sizeof(CheckPoint));
   newReplayTLI = checkPoint.ThisTimeLineID;
   prevReplayTLI = checkPoint.PrevTimeLineID;
  }
  else if (info == XLOG_END_OF_RECOVERY)
  {
   xl_end_of_recovery xlrec;

   memcpy(&xlrec, XLogRecGetData(xlogreader), sizeof(xl_end_of_recovery));
   newReplayTLI = xlrec.ThisTimeLineID;
   prevReplayTLI = xlrec.PrevTimeLineID;
  }

  if (newReplayTLI != *replayTLI)
  {
   /* Check that it's OK to switch to this TLI */
   checkTimeLineSwitch(xlogreader->EndRecPtr,
        newReplayTLI, prevReplayTLI, *replayTLI);

   /* Following WAL records should be run with new TLI */
   *replayTLI = newReplayTLI;
   switchedTLI = true;
  }
}

/*
  * Update shared replayEndRecPtr before replaying this record, so that
  * XLogFlush will update minRecoveryPoint correctly.
*/
SpinLockAcquire(&XLogRecoveryCtl->info_lck);
XLogRecoveryCtl->replayEndRecPtr = xlogreader->EndRecPtr;
XLogRecoveryCtl->replayEndTLI = *replayTLI;
SpinLockRelease(&XLogRecoveryCtl->info_lck);

/*
  * If we are attempting to enter Hot Standby mode, process XIDs we see
*/
if (standbyState >= STANDBY_INITIALIZED &&
  TransactionIdIsValid(record->xl_xid))
  RecordKnownAssignedTransactionIds(record->xl_xid);

/*
  * Some XLOG record types that are related to recovery are processed
  * directly here, rather than in xlog_redo()
*/
if (record->xl_rmid == RM_XLOG_ID)
  xlogrecovery_redo(xlogreader, *replayTLI);

/* Now apply the WAL record itself */
GetRmgr(record->xl_rmid).rm_redo(xlogreader);

/*
  * After redo, check whether the backup pages associated with the WAL
  * record are consistent with the existing pages. This check is done only
  * if consistency check is enabled for this record.
*/
if ((record->xl_info & XLR_CHECK_CONSISTENCY) != 0)
  verifyBackupPageConsistency(xlogreader);

/* Pop the error context stack */
error_context_stack = errcallback.previous;

/*
  * Update lastReplayedEndRecPtr after this record has been successfully
  * replayed.
*/
SpinLockAcquire(&XLogRecoveryCtl->info_lck);
XLogRecoveryCtl->lastReplayedReadRecPtr = xlogreader->ReadRecPtr;
XLogRecoveryCtl->lastReplayedEndRecPtr = xlogreader->EndRecPtr;
XLogRecoveryCtl->lastReplayedTLI = *replayTLI;
SpinLockRelease(&XLogRecoveryCtl->info_lck);

/* ------
  * Wakeup walsenders:
  *
  * On the standby, the WAL is flushed first (which will only wake up
  * physical walsenders) and then applied, which will only wake up logical
  * walsenders.
  *
  * Indeed, logical walsenders on standby can't decode and send data until
  * it's been applied.
  *
  * Physical walsenders don't need to be woken up during replay unless
  * cascading replication is allowed and time line change occurred (so that
  * they can notice that they are on a new time line).
  *
  * That's why the wake up conditions are for:
  *
  *  - physical walsenders in case of new time line and cascade
  *    replication is allowed
  *  - logical walsenders in case cascade replication is allowed (could not
  *    be created otherwise)
  * ------
*/
if (AllowCascadeReplication())
  WalSndWakeup(switchedTLI, true);

/*
  * If rm_redo called XLogRequestWalReceiverReply, then we wake up the
  * receiver so that it notices the updated lastReplayedEndRecPtr and sends
  * a reply to the primary.
*/
if (doRequestWalReceiverReply)
{
  doRequestWalReceiverReply = false;
  WalRcvForceReply();
}

/* Allow read-only connections if we're consistent now */
CheckRecoveryConsistency();

/* Is this a timeline switch? */
if (switchedTLI)
{
  /*
   * Before we continue on the new timeline, clean up any (possibly
   * bogus) future WAL segments on the old timeline.
*/
  RemoveNonParentXlogFiles(xlogreader->EndRecPtr, *replayTLI);

  /* Reset the prefetcher. */
  XLogPrefetchReconfigure();
}
}

/*
* Some XLOG RM record types that are directly related to WAL recovery are
* handled here rather than in the xlog_redo()
*/
static void
xlogrecovery_redo(XLogReaderState *record, TimeLineID replayTLI)
{
uint8  info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
XLogRecPtr lsn = record->EndRecPtr;

Assert(XLogRecGetRmid(record) == RM_XLOG_ID);

if (info == XLOG_OVERWRITE_CONTRECORD)
{
  /* Verify the payload of a XLOG_OVERWRITE_CONTRECORD record. */
  xl_overwrite_contrecord xlrec;

  memcpy(&xlrec, XLogRecGetData(record), sizeof(xl_overwrite_contrecord));
  if (xlrec.overwritten_lsn != record->overwrittenRecPtr)
   elog(FATAL, "mismatching overwritten LSN %X/%X -> %X/%X",
     LSN_FORMAT_ARGS(xlrec.overwritten_lsn),
     LSN_FORMAT_ARGS(record->overwrittenRecPtr));

  /* We have safely skipped the aborted record */
  abortedRecPtr = InvalidXLogRecPtr;
  missingContrecPtr = InvalidXLogRecPtr;

  ereport(LOG,
    (errmsg("successfully skipped missing contrecord at %X/%X, overwritten at %s",
      LSN_FORMAT_ARGS(xlrec.overwritten_lsn),
      timestamptz_to_str(xlrec.overwrite_time))));

  /* Verifying the record should only happen once */
  record->overwrittenRecPtr = InvalidXLogRecPtr;
}
else if (info == XLOG_BACKUP_END)
{
  XLogRecPtr startpoint;

  memcpy(&startpoint, XLogRecGetData(record), sizeof(startpoint));

  if (backupStartPoint == startpoint)
  {
   /*
    * We have reached the end of base backup, the point where
    * pg_backup_stop() was done.  The data on disk is now consistent
    * (assuming we have also reached minRecoveryPoint).  Set
    * backupEndPoint to the current LSN, so that the next call to
    * CheckRecoveryConsistency() will notice it and do the
    * end-of-backup processing.
*/
   elog(DEBUG1, "end of backup record reached");

   backupEndPoint = lsn;
  }
  else
   elog(DEBUG1, "saw end-of-backup record for backup starting at %X/%X, waiting for %X/%X",
     LSN_FORMAT_ARGS(startpoint), LSN_FORMAT_ARGS(backupStartPoint));
}
}

/*
* Verify that, in non-test mode, ./pg_tblspc doesn't contain any real
* directories.
*
* Replay of database creation XLOG records for databases that were later
* dropped can create fake directories in pg_tblspc.  By the time consistency
* is reached these directories should have been removed; here we verify
* that this did indeed happen.  This is to be called at the point where
* consistent state is reached.
*
* allow_in_place_tablespaces turns the PANIC into a WARNING, which is
* useful for testing purposes, and also allows for an escape hatch in case
* things go south.
*/
static void
CheckTablespaceDirectory(void)
{
DIR     *dir;
struct dirent *de;

dir = AllocateDir(PG_TBLSPC_DIR);
while ((de = ReadDir(dir, PG_TBLSPC_DIR)) != NULL)
{
  char  path[MAXPGPATH + sizeof(PG_TBLSPC_DIR)];

  /* Skip entries of non-oid names */
  if (strspn(de->d_name, "0123456789") != strlen(de->d_name))
   continue;

  snprintf(path, sizeof(path), "%s/%s", PG_TBLSPC_DIR, de->d_name);

  if (get_dirent_type(path, de, false, ERROR) != PGFILETYPE_LNK)
   ereport(allow_in_place_tablespaces ? WARNING : PANIC,
     (errcode(ERRCODE_DATA_CORRUPTED),
      errmsg("unexpected directory entry \"%s\" found in %s",
       de->d_name, PG_TBLSPC_DIR),
      errdetail("All directory entries in %s/ should be symbolic links.",
          PG_TBLSPC_DIR),
      errhint("Remove those directories, or set \"allow_in_place_tablespaces\" to ON transiently to let recovery complete.")));
}
}

/*
* Checks if recovery has reached a consistent state. When consistency is
* reached and we have a valid starting standby snapshot, tell postmaster
* that it can start accepting read-only connections.
*/
static void
CheckRecoveryConsistency(void)
{
XLogRecPtr lastReplayedEndRecPtr;
TimeLineID lastReplayedTLI;

/*
  * During crash recovery, we don't reach a consistent state until we've
  * replayed all the WAL.
*/
if (XLogRecPtrIsInvalid(minRecoveryPoint))
  return;

Assert(InArchiveRecovery);

/*
  * assume that we are called in the startup process, and hence don't need
  * a lock to read lastReplayedEndRecPtr
*/
lastReplayedEndRecPtr = XLogRecoveryCtl->lastReplayedEndRecPtr;
lastReplayedTLI = XLogRecoveryCtl->lastReplayedTLI;

/*
  * Have we reached the point where our base backup was completed?
*/
if (!XLogRecPtrIsInvalid(backupEndPoint) &&
  backupEndPoint <= lastReplayedEndRecPtr)
{
  XLogRecPtr saveBackupStartPoint = backupStartPoint;
  XLogRecPtr saveBackupEndPoint = backupEndPoint;

  elog(DEBUG1, "end of backup reached");

  /*
   * We have reached the end of base backup, as indicated by pg_control.
   * Update the control file accordingly.
*/
  ReachedEndOfBackup(lastReplayedEndRecPtr, lastReplayedTLI);
  backupStartPoint = InvalidXLogRecPtr;
  backupEndPoint = InvalidXLogRecPtr;
  backupEndRequired = false;

  ereport(LOG,
    (errmsg("completed backup recovery with redo LSN %X/%X and end LSN %X/%X",
      LSN_FORMAT_ARGS(saveBackupStartPoint),
      LSN_FORMAT_ARGS(saveBackupEndPoint))));
}

/*
  * Have we passed our safe starting point? Note that minRecoveryPoint is
  * known to be incorrectly set if recovering from a backup, until the
  * XLOG_BACKUP_END arrives to advise us of the correct minRecoveryPoint.
  * All we know prior to that is that we're not consistent yet.
*/
if (!reachedConsistency && !backupEndRequired &&
  minRecoveryPoint <= lastReplayedEndRecPtr)
{
  /*
   * Check to see if the XLOG sequence contained any unresolved
   * references to uninitialized pages.
*/
  XLogCheckInvalidPages();

  /*
   * Check that pg_tblspc doesn't contain any real directories. Replay
   * of Database/CREATE_* records may have created fictitious tablespace
   * directories that should have been removed by the time consistency
   * was reached.
*/
  CheckTablespaceDirectory();

  reachedConsistency = true;
  SendPostmasterSignal(PMSIGNAL_RECOVERY_CONSISTENT);
  ereport(LOG,
    (errmsg("consistent recovery state reached at %X/%X",
      LSN_FORMAT_ARGS(lastReplayedEndRecPtr))));
}

/*
  * Have we got a valid starting snapshot that will allow queries to be
  * run? If so, we can tell postmaster that the database is consistent now,
  * enabling connections.
*/
if (standbyState == STANDBY_SNAPSHOT_READY &&
  !LocalHotStandbyActive &&
  reachedConsistency &&
  IsUnderPostmaster)
{
  SpinLockAcquire(&XLogRecoveryCtl->info_lck);
  XLogRecoveryCtl->SharedHotStandbyActive = true;
  SpinLockRelease(&XLogRecoveryCtl->info_lck);

  LocalHotStandbyActive = true;

  SendPostmasterSignal(PMSIGNAL_BEGIN_HOT_STANDBY);
}
}

/*
* Error context callback for errors occurring during rm_redo().
*/
static void
rm_redo_error_callback(void *arg)
{
XLogReaderState *record = (XLogReaderState *) arg;
StringInfoData buf;

initStringInfo(&buf);
xlog_outdesc(&buf, record);
xlog_block_info(&buf, record);

/* translator: %s is a WAL record description */
errcontext("WAL redo at %X/%X for %s",
      LSN_FORMAT_ARGS(record->ReadRecPtr),
      buf.data);

pfree(buf.data);
}

/*
* Returns a string describing an XLogRecord, consisting of its identity
* optionally followed by a colon, a space, and a further description.
*/
void
xlog_outdesc(StringInfo buf, XLogReaderState *record)
{
RmgrData rmgr = GetRmgr(XLogRecGetRmid(record));
uint8  info = XLogRecGetInfo(record);
const char *id;

appendStringInfoString(buf, rmgr.rm_name);
appendStringInfoChar(buf, '/');

id = rmgr.rm_identify(info);
if (id == NULL)
  appendStringInfo(buf, "UNKNOWN (%X): ", info & ~XLR_INFO_MASK);
else
  appendStringInfo(buf, "%s: ", id);

rmgr.rm_desc(buf, record);
}

#ifdef WAL_DEBUG

static void
xlog_outrec(StringInfo buf, XLogReaderState *record)
{
appendStringInfo(buf, "prev %X/%X; xid %u",
      LSN_FORMAT_ARGS(XLogRecGetPrev(record)),
      XLogRecGetXid(record));

appendStringInfo(buf, "; len %u",
      XLogRecGetDataLen(record));

xlog_block_info(buf, record);
}
#endif       /* WAL_DEBUG */

/*
* Returns a string giving information about all the blocks in an
* XLogRecord.
*/
static void
xlog_block_info(StringInfo buf, XLogReaderState *record)
{
int   block_id;

/* decode block references */
for (block_id = 0; block_id <= XLogRecMaxBlockId(record); block_id++)
{
  RelFileLocator rlocator;
  ForkNumber forknum;
  BlockNumber blk;

  if (!XLogRecGetBlockTagExtended(record, block_id,
          &rlocator, &forknum, &blk, NULL))
   continue;

  if (forknum != MAIN_FORKNUM)
   appendStringInfo(buf, "; blkref #%d: rel %u/%u/%u, fork %u, blk %u",
        block_id,
        rlocator.spcOid, rlocator.dbOid,
        rlocator.relNumber,
        forknum,
        blk);
  else
   appendStringInfo(buf, "; blkref #%d: rel %u/%u/%u, blk %u",
        block_id,
        rlocator.spcOid, rlocator.dbOid,
        rlocator.relNumber,
        blk);
  if (XLogRecHasBlockImage(record, block_id))
   appendStringInfoString(buf, " FPW");
}
}

/*
* Check that it's OK to switch to new timeline during recovery.
*
* 'lsn' is the address of the shutdown checkpoint record we're about to
* replay. (Currently, timeline can only change at a shutdown checkpoint).
*/
static void
checkTimeLineSwitch(XLogRecPtr lsn, TimeLineID newTLI, TimeLineID prevTLI,
     TimeLineID replayTLI)
{
/* Check that the record agrees on what the current (old) timeline is */
if (prevTLI != replayTLI)
  ereport(PANIC,
    (errmsg("unexpected previous timeline ID %u (current timeline ID %u) in checkpoint record",
      prevTLI, replayTLI)));

/*
  * The new timeline better be in the list of timelines we expect to see,
  * according to the timeline history. It should also not decrease.
*/
if (newTLI < replayTLI || !tliInHistory(newTLI, expectedTLEs))
  ereport(PANIC,
    (errmsg("unexpected timeline ID %u (after %u) in checkpoint record",
      newTLI, replayTLI)));

/*
  * If we have not yet reached min recovery point, and we're about to
  * switch to a timeline greater than the timeline of the min recovery
  * point: trouble. After switching to the new timeline, we could not
  * possibly visit the min recovery point on the correct timeline anymore.
  * This can happen if there is a newer timeline in the archive that
  * branched before the timeline the min recovery point is on, and you
  * attempt to do PITR to the new timeline.
*/
if (!XLogRecPtrIsInvalid(minRecoveryPoint) &&
  lsn < minRecoveryPoint &&
  newTLI > minRecoveryPointTLI)
  ereport(PANIC,
    (errmsg("unexpected timeline ID %u in checkpoint record, before reaching minimum recovery point %X/%X on timeline %u",
      newTLI,
      LSN_FORMAT_ARGS(minRecoveryPoint),
      minRecoveryPointTLI)));

/* Looks good */
}

/*
* Extract timestamp from WAL record.
*
* If the record contains a timestamp, returns true, and saves the timestamp
* in *recordXtime. If the record type has no timestamp, returns false.
* Currently, only transaction commit/abort records and restore points contain
* timestamps.
*/
static bool
getRecordTimestamp(XLogReaderState *record, TimestampTz *recordXtime)
{
uint8  info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
uint8  xact_info = info & XLOG_XACT_OPMASK;
uint8  rmid = XLogRecGetRmid(record);

if (rmid == RM_XLOG_ID && info == XLOG_RESTORE_POINT)
{
  *recordXtime = ((xl_restore_point *) XLogRecGetData(record))->rp_time;
  return true;
}
if (rmid == RM_XACT_ID && (xact_info == XLOG_XACT_COMMIT ||
          xact_info == XLOG_XACT_COMMIT_PREPARED))
{
  *recordXtime = ((xl_xact_commit *) XLogRecGetData(record))->xact_time;
  return true;
}
if (rmid == RM_XACT_ID && (xact_info == XLOG_XACT_ABORT ||
          xact_info == XLOG_XACT_ABORT_PREPARED))
{
  *recordXtime = ((xl_xact_abort *) XLogRecGetData(record))->xact_time;
  return true;
}
return false;
}

/*
* Checks whether the current buffer page and backup page stored in the
* WAL record are consistent or not. Before comparing the two pages, a
* masking can be applied to the pages to ignore certain areas like hint bits,
* unused space between pd_lower and pd_upper among other things. This
* function should be called once WAL replay has been completed for a
* given record.
*/
static void
verifyBackupPageConsistency(XLogReaderState *record)
{
RmgrData rmgr = GetRmgr(XLogRecGetRmid(record));
RelFileLocator rlocator;
ForkNumber forknum;
BlockNumber blkno;
int   block_id;

/* Records with no backup blocks have no need for consistency checks. */
if (!XLogRecHasAnyBlockRefs(record))
  return;

Assert((XLogRecGetInfo(record) & XLR_CHECK_CONSISTENCY) != 0);

for (block_id = 0; block_id <= XLogRecMaxBlockId(record); block_id++)
{
  Buffer  buf;
  Page  page;

  if (!XLogRecGetBlockTagExtended(record, block_id,
          &rlocator, &forknum, &blkno, NULL))
  {
   /*
    * WAL record doesn't contain a block reference with the given id.
    * Do nothing.
*/
   continue;
  }

  Assert(XLogRecHasBlockImage(record, block_id));

  if (XLogRecBlockImageApply(record, block_id))
  {
   /*
    * WAL record has already applied the page, so bypass the
    * consistency check as that would result in comparing the full
    * page stored in the record with itself.
*/
   continue;
  }

  /*
   * Read the contents from the current buffer and store it in a
   * temporary page.
*/
  buf = XLogReadBufferExtended(rlocator, forknum, blkno,
          RBM_NORMAL_NO_LOG,
          InvalidBuffer);
  if (!BufferIsValid(buf))
   continue;

  LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
  page = BufferGetPage(buf);

  /*
   * Take a copy of the local page where WAL has been applied to have a
   * comparison base before masking it...
*/
  memcpy(replay_image_masked, page, BLCKSZ);

  /* No need for this page anymore now that a copy is in. */
  UnlockReleaseBuffer(buf);

  /*
   * If the block LSN is already ahead of this WAL record, we can't
   * expect contents to match.  This can happen if recovery is
   * restarted.
*/
  if (PageGetLSN(replay_image_masked) > record->EndRecPtr)
   continue;

  /*
   * Read the contents from the backup copy, stored in WAL record and
   * store it in a temporary page. There is no need to allocate a new
   * page here, a local buffer is fine to hold its contents and a mask
   * can be directly applied on it.
*/
  if (!RestoreBlockImage(record, block_id, primary_image_masked))
   ereport(ERROR,
     (errcode(ERRCODE_INTERNAL_ERROR),
      errmsg_internal("%s", record->errormsg_buf)));

  /*
   * If masking function is defined, mask both the primary and replay
   * images
*/
  if (rmgr.rm_mask != NULL)
  {
   rmgr.rm_mask(replay_image_masked, blkno);
   rmgr.rm_mask(primary_image_masked, blkno);
  }

  /* Time to compare the primary and replay images. */
  if (memcmp(replay_image_masked, primary_image_masked, BLCKSZ) != 0)
  {
   elog(FATAL,
     "inconsistent page found, rel %u/%u/%u, forknum %u, blkno %u",
     rlocator.spcOid, rlocator.dbOid, rlocator.relNumber,
     forknum, blkno);
  }
}
}

/*
* For point-in-time recovery, this function decides whether we want to
* stop applying the XLOG before the current record.
*
* Returns true if we are stopping, false otherwise. If stopping, some
* information is saved in recoveryStopXid et al for use in annotating the
* new timeline's history file.
*/
static bool
recoveryStopsBefore(XLogReaderState *record)
{
bool  stopsHere = false;
uint8  xact_info;
bool  isCommit;
TimestampTz recordXtime = 0;
TransactionId recordXid;

/*
  * Ignore recovery target settings when not in archive recovery (meaning
  * we are in crash recovery).
*/
if (!ArchiveRecoveryRequested)
  return false;

/* Check if we should stop as soon as reaching consistency */
if (recoveryTarget == RECOVERY_TARGET_IMMEDIATE && reachedConsistency)
{
  ereport(LOG,
    (errmsg("recovery stopping after reaching consistency")));

  recoveryStopAfter = false;
  recoveryStopXid = InvalidTransactionId;
  recoveryStopLSN = InvalidXLogRecPtr;
  recoveryStopTime = 0;
  recoveryStopName[0] = '\0';
  return true;
}

/* Check if target LSN has been reached */
if (recoveryTarget == RECOVERY_TARGET_LSN &&
  !recoveryTargetInclusive &&
  record->ReadRecPtr >= recoveryTargetLSN)
{
  recoveryStopAfter = false;
  recoveryStopXid = InvalidTransactionId;
  recoveryStopLSN = record->ReadRecPtr;
  recoveryStopTime = 0;
  recoveryStopName[0] = '\0';
  ereport(LOG,
    (errmsg("recovery stopping before WAL location (LSN) \"%X/%X\"",
      LSN_FORMAT_ARGS(recoveryStopLSN))));
  return true;
}

/* Otherwise we only consider stopping before COMMIT or ABORT records. */
if (XLogRecGetRmid(record) != RM_XACT_ID)
  return false;

xact_info = XLogRecGetInfo(record) & XLOG_XACT_OPMASK;

if (xact_info == XLOG_XACT_COMMIT)
{
  isCommit = true;
  recordXid = XLogRecGetXid(record);
}
else if (xact_info == XLOG_XACT_COMMIT_PREPARED)
{
  xl_xact_commit *xlrec = (xl_xact_commit *) XLogRecGetData(record);
  xl_xact_parsed_commit parsed;

  isCommit = true;
  ParseCommitRecord(XLogRecGetInfo(record),
        xlrec,
        &parsed);
  recordXid = parsed.twophase_xid;
}
else if (xact_info == XLOG_XACT_ABORT)
{
  isCommit = false;
  recordXid = XLogRecGetXid(record);
}
else if (xact_info == XLOG_XACT_ABORT_PREPARED)
{
  xl_xact_abort *xlrec = (xl_xact_abort *) XLogRecGetData(record);
  xl_xact_parsed_abort parsed;

  isCommit = false;
  ParseAbortRecord(XLogRecGetInfo(record),
       xlrec,
       &parsed);
  recordXid = parsed.twophase_xid;
}
else
  return false;

if (recoveryTarget == RECOVERY_TARGET_XID && !recoveryTargetInclusive)
{
  /*
   * There can be only one transaction end record with this exact
   * transactionid
   *
   * when testing for an xid, we MUST test for equality only, since
   * transactions are numbered in the order they start, not the order
   * they complete. A higher numbered xid will complete before you about
   * 50% of the time...
*/
  stopsHere = (recordXid == recoveryTargetXid);
}

/*
  * Note: we must fetch recordXtime regardless of recoveryTarget setting.
  * We don't expect getRecordTimestamp ever to fail, since we already know
  * this is a commit or abort record; but test its result anyway.
*/
if (getRecordTimestamp(record, &recordXtime) &&
  recoveryTarget == RECOVERY_TARGET_TIME)
{
  /*
   * There can be many transactions that share the same commit time, so
   * we stop after the last one, if we are inclusive, or stop at the
   * first one if we are exclusive
*/
  if (recoveryTargetInclusive)
   stopsHere = (recordXtime > recoveryTargetTime);
  else
   stopsHere = (recordXtime >= recoveryTargetTime);
}

if (stopsHere)
{
  recoveryStopAfter = false;
  recoveryStopXid = recordXid;
  recoveryStopTime = recordXtime;
  recoveryStopLSN = InvalidXLogRecPtr;
  recoveryStopName[0] = '\0';

  if (isCommit)
  {
   ereport(LOG,
     (errmsg("recovery stopping before commit of transaction %u, time %s",
       recoveryStopXid,
       timestamptz_to_str(recoveryStopTime))));
  }
  else
  {
   ereport(LOG,
     (errmsg("recovery stopping before abort of transaction %u, time %s",
       recoveryStopXid,
       timestamptz_to_str(recoveryStopTime))));
  }
}

return stopsHere;
}

/*
* Same as recoveryStopsBefore, but called after applying the record.
*
* We also track the timestamp of the latest applied COMMIT/ABORT
* record in XLogRecoveryCtl->recoveryLastXTime.
*/
static bool
recoveryStopsAfter(XLogReaderState *record)
{
uint8  info;
uint8  xact_info;
uint8  rmid;
TimestampTz recordXtime = 0;

/*
  * Ignore recovery target settings when not in archive recovery (meaning
  * we are in crash recovery).
*/
if (!ArchiveRecoveryRequested)
  return false;

info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
rmid = XLogRecGetRmid(record);

/*
  * There can be many restore points that share the same name; we stop at
  * the first one.
*/
if (recoveryTarget == RECOVERY_TARGET_NAME &&
  rmid == RM_XLOG_ID && info == XLOG_RESTORE_POINT)
{
  xl_restore_point *recordRestorePointData;

  recordRestorePointData = (xl_restore_point *) XLogRecGetData(record);

  if (strcmp(recordRestorePointData->rp_name, recoveryTargetName) == 0)
  {
   recoveryStopAfter = true;
   recoveryStopXid = InvalidTransactionId;
   recoveryStopLSN = InvalidXLogRecPtr;
   (void) getRecordTimestamp(record, &recoveryStopTime);
   strlcpy(recoveryStopName, recordRestorePointData->rp_name, MAXFNAMELEN);

   ereport(LOG,
     (errmsg("recovery stopping at restore point \"%s\", time %s",
       recoveryStopName,
       timestamptz_to_str(recoveryStopTime))));
   return true;
  }
}

/* Check if the target LSN has been reached */
if (recoveryTarget == RECOVERY_TARGET_LSN &&
  recoveryTargetInclusive &&
  record->ReadRecPtr >= recoveryTargetLSN)
{
  recoveryStopAfter = true;
  recoveryStopXid = InvalidTransactionId;
  recoveryStopLSN = record->ReadRecPtr;
  recoveryStopTime = 0;
  recoveryStopName[0] = '\0';
  ereport(LOG,
    (errmsg("recovery stopping after WAL location (LSN) \"%X/%X\"",
      LSN_FORMAT_ARGS(recoveryStopLSN))));
  return true;
}

if (rmid != RM_XACT_ID)
  return false;

xact_info = info & XLOG_XACT_OPMASK;

if (xact_info == XLOG_XACT_COMMIT ||
  xact_info == XLOG_XACT_COMMIT_PREPARED ||
  xact_info == XLOG_XACT_ABORT ||
  xact_info == XLOG_XACT_ABORT_PREPARED)
{
  TransactionId recordXid;

  /* Update the last applied transaction timestamp */
  if (getRecordTimestamp(record, &recordXtime))
   SetLatestXTime(recordXtime);

  /* Extract the XID of the committed/aborted transaction */
  if (xact_info == XLOG_XACT_COMMIT_PREPARED)
  {
   xl_xact_commit *xlrec = (xl_xact_commit *) XLogRecGetData(record);
   xl_xact_parsed_commit parsed;

   ParseCommitRecord(XLogRecGetInfo(record),
         xlrec,
         &parsed);
   recordXid = parsed.twophase_xid;
  }
  else if (xact_info == XLOG_XACT_ABORT_PREPARED)
  {
   xl_xact_abort *xlrec = (xl_xact_abort *) XLogRecGetData(record);
   xl_xact_parsed_abort parsed;

   ParseAbortRecord(XLogRecGetInfo(record),
        xlrec,
        &parsed);
   recordXid = parsed.twophase_xid;
  }
  else
   recordXid = XLogRecGetXid(record);

  /*
   * There can be only one transaction end record with this exact
   * transactionid
   *
   * when testing for an xid, we MUST test for equality only, since
   * transactions are numbered in the order they start, not the order
   * they complete. A higher numbered xid will complete before you about
   * 50% of the time...
*/
  if (recoveryTarget == RECOVERY_TARGET_XID && recoveryTargetInclusive &&
   recordXid == recoveryTargetXid)
  {
   recoveryStopAfter = true;
   recoveryStopXid = recordXid;
   recoveryStopTime = recordXtime;
   recoveryStopLSN = InvalidXLogRecPtr;
   recoveryStopName[0] = '\0';

   if (xact_info == XLOG_XACT_COMMIT ||
    xact_info == XLOG_XACT_COMMIT_PREPARED)
   {
    ereport(LOG,
      (errmsg("recovery stopping after commit of transaction %u, time %s",
        recoveryStopXid,
        timestamptz_to_str(recoveryStopTime))));
   }
   else if (xact_info == XLOG_XACT_ABORT ||
      xact_info == XLOG_XACT_ABORT_PREPARED)
   {
    ereport(LOG,
      (errmsg("recovery stopping after abort of transaction %u, time %s",
        recoveryStopXid,
        timestamptz_to_str(recoveryStopTime))));
   }
   return true;
  }
}

/* Check if we should stop as soon as reaching consistency */
if (recoveryTarget == RECOVERY_TARGET_IMMEDIATE && reachedConsistency)
{
  ereport(LOG,
    (errmsg("recovery stopping after reaching consistency")));

  recoveryStopAfter = true;
  recoveryStopXid = InvalidTransactionId;
  recoveryStopTime = 0;
  recoveryStopLSN = InvalidXLogRecPtr;
  recoveryStopName[0] = '\0';
  return true;
}

return false;
}

/*
* Create a comment for the history file to explain why and where
* timeline changed.
*/
static char *
getRecoveryStopReason(void)
{
char  reason[200];

if (recoveryTarget == RECOVERY_TARGET_XID)
  snprintf(reason, sizeof(reason),
     "%s transaction %u",
     recoveryStopAfter ? "after" : "before",
     recoveryStopXid);
else if (recoveryTarget == RECOVERY_TARGET_TIME)
  snprintf(reason, sizeof(reason),
     "%s %s\n",
     recoveryStopAfter ? "after" : "before",
     timestamptz_to_str(recoveryStopTime));
else if (recoveryTarget == RECOVERY_TARGET_LSN)
  snprintf(reason, sizeof(reason),
     "%s LSN %X/%X\n",
     recoveryStopAfter ? "after" : "before",
     LSN_FORMAT_ARGS(recoveryStopLSN));
else if (recoveryTarget == RECOVERY_TARGET_NAME)
  snprintf(reason, sizeof(reason),
     "at restore point \"%s\"",
     recoveryStopName);
else if (recoveryTarget == RECOVERY_TARGET_IMMEDIATE)
  snprintf(reason, sizeof(reason), "reached consistency");
else
  snprintf(reason, sizeof(reason), "no recovery target specified");

return pstrdup(reason);
}

/*
* Wait until shared recoveryPauseState is set to RECOVERY_NOT_PAUSED.
*
* endOfRecovery is true if the recovery target is reached and
* the paused state starts at the end of recovery because of
* recovery_target_action=pause, and false otherwise.
*/
static void
recoveryPausesHere(bool endOfRecovery)
{
/* Don't pause unless users can connect! */
if (!LocalHotStandbyActive)
  return;

/* Don't pause after standby promotion has been triggered */
if (LocalPromoteIsTriggered)
  return;

if (endOfRecovery)
  ereport(LOG,
    (errmsg("pausing at the end of recovery"),
     errhint("Execute pg_wal_replay_resume() to promote.")));
else
  ereport(LOG,
    (errmsg("recovery has paused"),
     errhint("Execute pg_wal_replay_resume() to continue.")));

/* loop until recoveryPauseState is set to RECOVERY_NOT_PAUSED */
while (GetRecoveryPauseState() != RECOVERY_NOT_PAUSED)
{
  ProcessStartupProcInterrupts();
  if (CheckForStandbyTrigger())
   return;

  /*
   * If recovery pause is requested then set it paused.  While we are in
   * the loop, user might resume and pause again so set this every time.
*/
  ConfirmRecoveryPaused();

  /*
   * We wait on a condition variable that will wake us as soon as the
   * pause ends, but we use a timeout so we can check the above exit
   * condition periodically too.
*/
  ConditionVariableTimedSleep(&XLogRecoveryCtl->recoveryNotPausedCV, 1000,
         WAIT_EVENT_RECOVERY_PAUSE);
}
ConditionVariableCancelSleep();
}

/*
* When recovery_min_apply_delay is set, we wait long enough to make sure
* certain record types are applied at least that interval behind the primary.
*
* Returns true if we waited.
*
* Note that the delay is calculated between the WAL record log time and
* the current time on standby. We would prefer to keep track of when this
* standby received each WAL record, which would allow a more consistent
* approach and one not affected by time synchronisation issues, but that
* is significantly more effort and complexity for little actual gain in
* usability.
*/
static bool
recoveryApplyDelay(XLogReaderState *record)
{
uint8  xact_info;
TimestampTz xtime;
TimestampTz delayUntil;
long  msecs;

/* nothing to do if no delay configured */
if (recovery_min_apply_delay <= 0)
  return false;

/* no delay is applied on a database not yet consistent */
if (!reachedConsistency)
  return false;

/* nothing to do if crash recovery is requested */
if (!ArchiveRecoveryRequested)
  return false;

/*
  * Is it a COMMIT record?
  *
  * We deliberately choose not to delay aborts since they have no effect on
  * MVCC. We already allow replay of records that don't have a timestamp,
  * so there is already opportunity for issues caused by early conflicts on
  * standbys.
*/
if (XLogRecGetRmid(record) != RM_XACT_ID)
  return false;

xact_info = XLogRecGetInfo(record) & XLOG_XACT_OPMASK;

if (xact_info != XLOG_XACT_COMMIT &&
  xact_info != XLOG_XACT_COMMIT_PREPARED)
  return false;

if (!getRecordTimestamp(record, &xtime))
  return false;

delayUntil = TimestampTzPlusMilliseconds(xtime, recovery_min_apply_delay);

/*
  * Exit without arming the latch if it's already past time to apply this
  * record
*/
msecs = TimestampDifferenceMilliseconds(GetCurrentTimestamp(), delayUntil);
if (msecs <= 0)
  return false;

while (true)
{
  ResetLatch(&XLogRecoveryCtl->recoveryWakeupLatch);

  /* This might change recovery_min_apply_delay. */
  ProcessStartupProcInterrupts();

  if (CheckForStandbyTrigger())
   break;

  /*
   * Recalculate delayUntil as recovery_min_apply_delay could have
   * changed while waiting in this loop.
*/
  delayUntil = TimestampTzPlusMilliseconds(xtime, recovery_min_apply_delay);

  /*
   * Wait for difference between GetCurrentTimestamp() and delayUntil.
*/
  msecs = TimestampDifferenceMilliseconds(GetCurrentTimestamp(),
            delayUntil);

  if (msecs <= 0)
   break;

  elog(DEBUG2, "recovery apply delay %ld milliseconds", msecs);

  (void) WaitLatch(&XLogRecoveryCtl->recoveryWakeupLatch,
       WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
       msecs,
       WAIT_EVENT_RECOVERY_APPLY_DELAY);
}
return true;
}

/*
* Get the current state of the recovery pause request.
*/
RecoveryPauseState
GetRecoveryPauseState(void)
{
RecoveryPauseState state;

SpinLockAcquire(&XLogRecoveryCtl->info_lck);
state = XLogRecoveryCtl->recoveryPauseState;
SpinLockRelease(&XLogRecoveryCtl->info_lck);

return state;
}

/*
* Set the recovery pause state.
*
* If recovery pause is requested then sets the recovery pause state to
* 'pause requested' if it is not already 'paused'.  Otherwise, sets it
* to 'not paused' to resume the recovery.  The recovery pause will be
* confirmed by the ConfirmRecoveryPaused.
*/
void
SetRecoveryPause(bool recoveryPause)
{
SpinLockAcquire(&XLogRecoveryCtl->info_lck);

if (!recoveryPause)
  XLogRecoveryCtl->recoveryPauseState = RECOVERY_NOT_PAUSED;
else if (XLogRecoveryCtl->recoveryPauseState == RECOVERY_NOT_PAUSED)
  XLogRecoveryCtl->recoveryPauseState = RECOVERY_PAUSE_REQUESTED;

SpinLockRelease(&XLogRecoveryCtl->info_lck);

if (!recoveryPause)
  ConditionVariableBroadcast(&XLogRecoveryCtl->recoveryNotPausedCV);
}

/*
* Confirm the recovery pause by setting the recovery pause state to
* RECOVERY_PAUSED.
*/
static void
ConfirmRecoveryPaused(void)
{
/* If recovery pause is requested then set it paused */
SpinLockAcquire(&XLogRecoveryCtl->info_lck);
if (XLogRecoveryCtl->recoveryPauseState == RECOVERY_PAUSE_REQUESTED)
  XLogRecoveryCtl->recoveryPauseState = RECOVERY_PAUSED;
SpinLockRelease(&XLogRecoveryCtl->info_lck);
}

/*
* Attempt to read the next XLOG record.
*
* Before first call, the reader needs to be positioned to the first record
* by calling XLogPrefetcherBeginRead().
*
* If no valid record is available, returns NULL, or fails if emode is PANIC.
* (emode must be either PANIC, LOG). In standby mode, retries until a valid
* record is available.
*/
static XLogRecord *
ReadRecord(XLogPrefetcher *xlogprefetcher, int emode,
     bool fetching_ckpt, TimeLineID replayTLI)
{
XLogRecord *record;
XLogReaderState *xlogreader = XLogPrefetcherGetReader(xlogprefetcher);
XLogPageReadPrivate *private = (XLogPageReadPrivate *) xlogreader->private_data;

/* Pass through parameters to XLogPageRead */
private->fetching_ckpt = fetching_ckpt;
private->emode = emode;
private->randAccess = (xlogreader->ReadRecPtr == InvalidXLogRecPtr);
private->replayTLI = replayTLI;

/* This is the first attempt to read this page. */
lastSourceFailed = false;

for (;;)
{
  char    *errormsg;

  record = XLogPrefetcherReadRecord(xlogprefetcher, &errormsg);
  if (record == NULL)
  {
   /*
    * When we find that WAL ends in an incomplete record, keep track
    * of that record.  After recovery is done, we'll write a record
    * to indicate to downstream WAL readers that that portion is to
    * be ignored.
    *
    * However, when ArchiveRecoveryRequested = true, we're going to
    * switch to a new timeline at the end of recovery. We will only
    * copy WAL over to the new timeline up to the end of the last
    * complete record, so if we did this, we would later create an
    * overwrite contrecord in the wrong place, breaking everything.
*/
   if (!ArchiveRecoveryRequested &&
    !XLogRecPtrIsInvalid(xlogreader->abortedRecPtr))
   {
    abortedRecPtr = xlogreader->abortedRecPtr;
    missingContrecPtr = xlogreader->missingContrecPtr;
   }

   if (readFile >= 0)
   {
    close(readFile);
    readFile = -1;
   }

   /*
    * We only end up here without a message when XLogPageRead()
    * failed - in that case we already logged something. In
    * StandbyMode that only happens if we have been triggered, so we
    * shouldn't loop anymore in that case.
*/
   if (errormsg)
    ereport(emode_for_corrupt_record(emode, xlogreader->EndRecPtr),
      (errmsg_internal("%s", errormsg) /* already translated */ ));
  }

  /*
   * Check page TLI is one of the expected values.
*/
  else if (!tliInHistory(xlogreader->latestPageTLI, expectedTLEs))
  {
   char  fname[MAXFNAMELEN];
   XLogSegNo segno;
   int32  offset;

   XLByteToSeg(xlogreader->latestPagePtr, segno, wal_segment_size);
   offset = XLogSegmentOffset(xlogreader->latestPagePtr,
            wal_segment_size);
   XLogFileName(fname, xlogreader->seg.ws_tli, segno,
       wal_segment_size);
   ereport(emode_for_corrupt_record(emode, xlogreader->EndRecPtr),
     (errmsg("unexpected timeline ID %u in WAL segment %s, LSN %X/%X, offset %u",
       xlogreader->latestPageTLI,
       fname,
       LSN_FORMAT_ARGS(xlogreader->latestPagePtr),
       offset)));
   record = NULL;
  }

  if (record)
  {
   /* Great, got a record */
   return record;
  }
  else
  {
   /* No valid record available from this source */
   lastSourceFailed = true;

   /*
    * If archive recovery was requested, but we were still doing
    * crash recovery, switch to archive recovery and retry using the
    * offline archive. We have now replayed all the valid WAL in
    * pg_wal, so we are presumably now consistent.
    *
    * We require that there's at least some valid WAL present in
    * pg_wal, however (!fetching_ckpt).  We could recover using the
    * WAL from the archive, even if pg_wal is completely empty, but
    * we'd have no idea how far we'd have to replay to reach
    * consistency.  So err on the safe side and give up.
*/
   if (!InArchiveRecovery && ArchiveRecoveryRequested &&
    !fetching_ckpt)
   {
    ereport(DEBUG1,
      (errmsg_internal("reached end of WAL in pg_wal, entering archive recovery")));
    InArchiveRecovery = true;
    if (StandbyModeRequested)
     EnableStandbyMode();

    SwitchIntoArchiveRecovery(xlogreader->EndRecPtr, replayTLI);
    minRecoveryPoint = xlogreader->EndRecPtr;
    minRecoveryPointTLI = replayTLI;

    CheckRecoveryConsistency();

    /*
     * Before we retry, reset lastSourceFailed and currentSource
     * so that we will check the archive next.
*/
    lastSourceFailed = false;
    currentSource = XLOG_FROM_ANY;

    continue;
   }

   /* In standby mode, loop back to retry. Otherwise, give up. */
   if (StandbyMode && !CheckForStandbyTrigger())
    continue;
   else
    return NULL;
  }
}
}

/*
* Read the XLOG page containing targetPagePtr into readBuf (if not read
* already).  Returns number of bytes read, if the page is read successfully,
* or XLREAD_FAIL in case of errors.  When errors occur, they are ereport'ed,
* but only if they have not been previously reported.
*
* See XLogReaderRoutine.page_read for more details.
*
* While prefetching, xlogreader->nonblocking may be set.  In that case,
* returns XLREAD_WOULDBLOCK if we'd otherwise have to wait for more WAL.
*
* This is responsible for restoring files from archive as needed, as well
* as for waiting for the requested WAL record to arrive in standby mode.
*
* xlogreader->private_data->emode specifies the log level used for reporting
* "file not found" or "end of WAL" situations in archive recovery, or in
* standby mode when promotion is triggered. If set to WARNING or below,
* XLogPageRead() returns XLREAD_FAIL in those situations, on higher log
* levels the ereport() won't return.
*
* In standby mode, if after a successful return of XLogPageRead() the
* caller finds the record it's interested in to be broken, it should
* ereport the error with the level determined by
* emode_for_corrupt_record(), and then set lastSourceFailed
* and call XLogPageRead() again with the same arguments. This lets
* XLogPageRead() to try fetching the record from another source, or to
* sleep and retry.
*/
static int
XLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr, int reqLen,
    XLogRecPtr targetRecPtr, char *readBuf)
{
XLogPageReadPrivate *private =
  (XLogPageReadPrivate *) xlogreader->private_data;
int   emode = private->emode;
uint32  targetPageOff;
XLogSegNo targetSegNo PG_USED_FOR_ASSERTS_ONLY;
int   r;
instr_time io_start;

XLByteToSeg(targetPagePtr, targetSegNo, wal_segment_size);
targetPageOff = XLogSegmentOffset(targetPagePtr, wal_segment_size);

/*
  * See if we need to switch to a new segment because the requested record
  * is not in the currently open one.
*/
if (readFile >= 0 &&
  !XLByteInSeg(targetPagePtr, readSegNo, wal_segment_size))
{
  /*
   * Request a restartpoint if we've replayed too much xlog since the
   * last one.
*/
  if (ArchiveRecoveryRequested && IsUnderPostmaster)
  {
   if (XLogCheckpointNeeded(readSegNo))
   {
    (void) GetRedoRecPtr();
    if (XLogCheckpointNeeded(readSegNo))
     RequestCheckpoint(CHECKPOINT_CAUSE_XLOG);
   }
  }

  close(readFile);
  readFile = -1;
  readSource = XLOG_FROM_ANY;
}

XLByteToSeg(targetPagePtr, readSegNo, wal_segment_size);

retry:
/* See if we need to retrieve more data */
if (readFile < 0 ||
  (readSource == XLOG_FROM_STREAM &&
   flushedUpto < targetPagePtr + reqLen))
{
  if (readFile >= 0 &&
   xlogreader->nonblocking &&
   readSource == XLOG_FROM_STREAM &&
   flushedUpto < targetPagePtr + reqLen)
   return XLREAD_WOULDBLOCK;

  switch (WaitForWALToBecomeAvailable(targetPagePtr + reqLen,
           private->randAccess,
           private->fetching_ckpt,
           targetRecPtr,
           private->replayTLI,
           xlogreader->EndRecPtr,
           xlogreader->nonblocking))
  {
   case XLREAD_WOULDBLOCK:
    return XLREAD_WOULDBLOCK;
   case XLREAD_FAIL:
    if (readFile >= 0)
     close(readFile);
    readFile = -1;
    readLen = 0;
    readSource = XLOG_FROM_ANY;
    return XLREAD_FAIL;
   case XLREAD_SUCCESS:
    break;
  }
}

/*
  * At this point, we have the right segment open and if we're streaming we
  * know the requested record is in it.
*/
Assert(readFile != -1);

/*
  * If the current segment is being streamed from the primary, calculate
  * how much of the current page we have received already. We know the
  * requested record has been received, but this is for the benefit of
  * future calls, to allow quick exit at the top of this function.
*/
if (readSource == XLOG_FROM_STREAM)
{
  if (((targetPagePtr) / XLOG_BLCKSZ) != (flushedUpto / XLOG_BLCKSZ))
   readLen = XLOG_BLCKSZ;
  else
   readLen = XLogSegmentOffset(flushedUpto, wal_segment_size) -
    targetPageOff;
}
else
  readLen = XLOG_BLCKSZ;

/* Read the requested page */
readOff = targetPageOff;

/* Measure I/O timing when reading segment */
io_start = pgstat_prepare_io_time(track_wal_io_timing);

pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
r = pg_pread(readFile, readBuf, XLOG_BLCKSZ, (off_t) readOff);
if (r != XLOG_BLCKSZ)
{
  char  fname[MAXFNAMELEN];
  int   save_errno = errno;

  pgstat_report_wait_end();

  pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_NORMAL, IOOP_READ,
        io_start, 1, r);

  XLogFileName(fname, curFileTLI, readSegNo, wal_segment_size);
  if (r < 0)
  {
   errno = save_errno;
   ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
     (errcode_for_file_access(),
      errmsg("could not read from WAL segment %s, LSN %X/%X, offset %u: %m",
       fname, LSN_FORMAT_ARGS(targetPagePtr),
       readOff)));
  }
  else
   ereport(emode_for_corrupt_record(emode, targetPagePtr + reqLen),
     (errcode(ERRCODE_DATA_CORRUPTED),
      errmsg("could not read from WAL segment %s, LSN %X/%X, offset %u: read %d of %zu",
       fname, LSN_FORMAT_ARGS(targetPagePtr),
       readOff, r, (Size) XLOG_BLCKSZ)));
  goto next_record_is_invalid;
}
pgstat_report_wait_end();

pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_NORMAL, IOOP_READ,
       io_start, 1, r);

Assert(targetSegNo == readSegNo);
Assert(targetPageOff == readOff);
Assert(reqLen <= readLen);

xlogreader->seg.ws_tli = curFileTLI;

/*
  * Check the page header immediately, so that we can retry immediately if
  * it's not valid. This may seem unnecessary, because ReadPageInternal()
  * validates the page header anyway, and would propagate the failure up to
  * ReadRecord(), which would retry. However, there's a corner case with
  * continuation records, if a record is split across two pages such that
  * we would need to read the two pages from different sources across two
  * WAL segments.
  *
  * The first page is only available locally, in pg_wal, because it's
  * already been recycled on the primary. The second page, however, is not
  * present in pg_wal, and we should stream it from the primary. There is a
  * recycled WAL segment present in pg_wal, with garbage contents, however.
  * We would read the first page from the local WAL segment, but when
  * reading the second page, we would read the bogus, recycled, WAL
  * segment. If we didn't catch that case here, we would never recover,
  * because ReadRecord() would retry reading the whole record from the
  * beginning.
  *
  * Of course, this only catches errors in the page header, which is what
  * happens in the case of a recycled WAL segment. Other kinds of errors or
  * corruption still has the same problem. But this at least fixes the
  * common case, which can happen as part of normal operation.
  *
  * Validating the page header is cheap enough that doing it twice
  * shouldn't be a big deal from a performance point of view.
  *
  * When not in standby mode, an invalid page header should cause recovery
  * to end, not retry reading the page, so we don't need to validate the
  * page header here for the retry. Instead, ReadPageInternal() is
  * responsible for the validation.
*/
if (StandbyMode &&
  (targetPagePtr % wal_segment_size) == 0 &&
  !XLogReaderValidatePageHeader(xlogreader, targetPagePtr, readBuf))
{
  /*
   * Emit this error right now then retry this page immediately. Use
   * errmsg_internal() because the message was already translated.
*/
  if (xlogreader->errormsg_buf[0])
   ereport(emode_for_corrupt_record(emode, xlogreader->EndRecPtr),
     (errmsg_internal("%s", xlogreader->errormsg_buf)));

  /* reset any error XLogReaderValidatePageHeader() might have set */
  XLogReaderResetError(xlogreader);
  goto next_record_is_invalid;
}

return readLen;

next_record_is_invalid:

/*
  * If we're reading ahead, give up fast.  Retries and error reporting will
  * be handled by a later read when recovery catches up to this point.
*/
if (xlogreader->nonblocking)
  return XLREAD_WOULDBLOCK;

lastSourceFailed = true;

if (readFile >= 0)
  close(readFile);
readFile = -1;
readLen = 0;
readSource = XLOG_FROM_ANY;

/* In standby-mode, keep trying */
if (StandbyMode)
  goto retry;
else
  return XLREAD_FAIL;
}

/*
* Open the WAL segment containing WAL location 'RecPtr'.
*
* The segment can be fetched via restore_command, or via walreceiver having
* streamed the record, or it can already be present in pg_wal. Checking
* pg_wal is mainly for crash recovery, but it will be polled in standby mode
* too, in case someone copies a new segment directly to pg_wal. That is not
* documented or recommended, though.
*
* If 'fetching_ckpt' is true, we're fetching a checkpoint record, and should
* prepare to read WAL starting from RedoStartLSN after this.
*
* 'RecPtr' might not point to the beginning of the record we're interested
* in, it might also point to the page or segment header. In that case,
* 'tliRecPtr' is the position of the WAL record we're interested in. It is
* used to decide which timeline to stream the requested WAL from.
*
* 'replayLSN' is the current replay LSN, so that if we scan for new
* timelines, we can reject a switch to a timeline that branched off before
* this point.
*
* If the record is not immediately available, the function returns false
* if we're not in standby mode. In standby mode, waits for it to become
* available.
*
* When the requested record becomes available, the function opens the file
* containing it (if not open already), and returns XLREAD_SUCCESS. When end
* of standby mode is triggered by the user, and there is no more WAL
* available, returns XLREAD_FAIL.
*
* If nonblocking is true, then give up immediately if we can't satisfy the
* request, returning XLREAD_WOULDBLOCK instead of waiting.
*/
static XLogPageReadResult
WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
       bool fetching_ckpt, XLogRecPtr tliRecPtr,
       TimeLineID replayTLI, XLogRecPtr replayLSN,
       bool nonblocking)
{
static TimestampTz last_fail_time = 0;
TimestampTz now;
bool  streaming_reply_sent = false;

/*-------
  * Standby mode is implemented by a state machine:
  *
  * 1. Read from either archive or pg_wal (XLOG_FROM_ARCHIVE), or just
  *   pg_wal (XLOG_FROM_PG_WAL)
  * 2. Check for promotion trigger request
  * 3. Read from primary server via walreceiver (XLOG_FROM_STREAM)
  * 4. Rescan timelines
  * 5. Sleep wal_retrieve_retry_interval milliseconds, and loop back to 1.
  *
  * Failure to read from the current source advances the state machine to
  * the next state.
  *
  * 'currentSource' indicates the current state. There are no currentSource
  * values for "check trigger", "rescan timelines", and "sleep" states,
  * those actions are taken when reading from the previous source fails, as
  * part of advancing to the next state.
  *
  * If standby mode is turned off while reading WAL from stream, we move
  * to XLOG_FROM_ARCHIVE and reset lastSourceFailed, to force fetching
  * the files (which would be required at end of recovery, e.g., timeline
  * history file) from archive or pg_wal. We don't need to kill WAL receiver
  * here because it's already stopped when standby mode is turned off at
  * the end of recovery.
  *-------
*/
if (!InArchiveRecovery)
  currentSource = XLOG_FROM_PG_WAL;
else if (currentSource == XLOG_FROM_ANY ||
    (!StandbyMode && currentSource == XLOG_FROM_STREAM))
{
  lastSourceFailed = false;
  currentSource = XLOG_FROM_ARCHIVE;
}

for (;;)
{
  XLogSource oldSource = currentSource;
  bool  startWalReceiver = false;

  /*
   * First check if we failed to read from the current source, and
   * advance the state machine if so. The failure to read might've
   * happened outside this function, e.g when a CRC check fails on a
   * record, or within this loop.
*/
  if (lastSourceFailed)
  {
   /*
    * Don't allow any retry loops to occur during nonblocking
    * readahead.  Let the caller process everything that has been
    * decoded already first.
*/
   if (nonblocking)
    return XLREAD_WOULDBLOCK;

   switch (currentSource)
   {
    case XLOG_FROM_ARCHIVE:
    case XLOG_FROM_PG_WAL:

     /*
      * Check to see if promotion is requested. Note that we do
      * this only after failure, so when you promote, we still
      * finish replaying as much as we can from archive and
      * pg_wal before failover.
*/
     if (StandbyMode && CheckForStandbyTrigger())
     {
      XLogShutdownWalRcv();
      return XLREAD_FAIL;
     }

     /*
      * Not in standby mode, and we've now tried the archive
      * and pg_wal.
*/
     if (!StandbyMode)
      return XLREAD_FAIL;

     /*
      * Move to XLOG_FROM_STREAM state, and set to start a
      * walreceiver if necessary.
*/
     currentSource = XLOG_FROM_STREAM;
     startWalReceiver = true;
     break;

    case XLOG_FROM_STREAM:

     /*
      * Failure while streaming. Most likely, we got here
      * because streaming replication was terminated, or
      * promotion was triggered. But we also get here if we
      * find an invalid record in the WAL streamed from the
      * primary, in which case something is seriously wrong.
      * There's little chance that the problem will just go
      * away, but PANIC is not good for availability either,
      * especially in hot standby mode. So, we treat that the
      * same as disconnection, and retry from archive/pg_wal
      * again. The WAL in the archive should be identical to
      * what was streamed, so it's unlikely that it helps, but
      * one can hope...
*/

     /*
      * We should be able to move to XLOG_FROM_STREAM only in
      * standby mode.
*/
     Assert(StandbyMode);

     /*
      * Before we leave XLOG_FROM_STREAM state, make sure that
      * walreceiver is not active, so that it won't overwrite
      * WAL that we restore from archive.
      *
      * If walreceiver is actively streaming (or attempting to
      * connect), we must shut it down. However, if it's
      * already in WAITING state (e.g., due to timeline
      * divergence), we only need to reset the install flag to
      * allow archive restoration.
*/
     if (WalRcvStreaming())
      XLogShutdownWalRcv();
     else
     {
      ResetInstallXLogFileSegmentActive();
     }

     /*
      * Before we sleep, re-scan for possible new timelines if
      * we were requested to recover to the latest timeline.
*/
     if (recoveryTargetTimeLineGoal == RECOVERY_TARGET_TIMELINE_LATEST)
     {
      if (rescanLatestTimeLine(replayTLI, replayLSN))
      {
       currentSource = XLOG_FROM_ARCHIVE;
       break;
      }
     }

     /*
      * XLOG_FROM_STREAM is the last state in our state
      * machine, so we've exhausted all the options for
      * obtaining the requested WAL. We're going to loop back
      * and retry from the archive, but if it hasn't been long
      * since last attempt, sleep wal_retrieve_retry_interval
      * milliseconds to avoid busy-waiting.
*/
     now = GetCurrentTimestamp();
     if (!TimestampDifferenceExceeds(last_fail_time, now,
             wal_retrieve_retry_interval))
     {
      long  wait_time;

      wait_time = wal_retrieve_retry_interval -
       TimestampDifferenceMilliseconds(last_fail_time, now);

      elog(LOG, "waiting for WAL to become available at %X/%X",
        LSN_FORMAT_ARGS(RecPtr));

      /* Do background tasks that might benefit us later. */
      KnownAssignedTransactionIdsIdleMaintenance();

      (void) WaitLatch(&XLogRecoveryCtl->recoveryWakeupLatch,
           WL_LATCH_SET | WL_TIMEOUT |
           WL_EXIT_ON_PM_DEATH,
           wait_time,
           WAIT_EVENT_RECOVERY_RETRIEVE_RETRY_INTERVAL);
      ResetLatch(&XLogRecoveryCtl->recoveryWakeupLatch);
      now = GetCurrentTimestamp();

      /* Handle interrupt signals of startup process */
      ProcessStartupProcInterrupts();
     }
     last_fail_time = now;
     currentSource = XLOG_FROM_ARCHIVE;
     break;

    default:
     elog(ERROR, "unexpected WAL source %d", currentSource);
   }
  }
  else if (currentSource == XLOG_FROM_PG_WAL)
  {
   /*
    * We just successfully read a file in pg_wal. We prefer files in
    * the archive over ones in pg_wal, so try the next file again
    * from the archive first.
*/
   if (InArchiveRecovery)
    currentSource = XLOG_FROM_ARCHIVE;
  }

  if (currentSource != oldSource)
   elog(DEBUG2, "switched WAL source from %s to %s after %s",
     xlogSourceNames[oldSource], xlogSourceNames[currentSource],
     lastSourceFailed ? "failure" : "success");

  /*
   * We've now handled possible failure. Try to read from the chosen
   * source.
*/
  lastSourceFailed = false;

  switch (currentSource)
  {
   case XLOG_FROM_ARCHIVE:
   case XLOG_FROM_PG_WAL:

    /*
     * WAL receiver must not be running when reading WAL from
     * archive or pg_wal.
*/
    Assert(!WalRcvStreaming());

    /* Close any old file we might have open. */
    if (readFile >= 0)
    {
     close(readFile);
     readFile = -1;
    }
    /* Reset curFileTLI if random fetch. */
    if (randAccess)
     curFileTLI = 0;

    /*
     * Try to restore the file from archive, or read an existing
     * file from pg_wal.
*/
    readFile = XLogFileReadAnyTLI(readSegNo,
             currentSource == XLOG_FROM_ARCHIVE ? XLOG_FROM_ANY :
             currentSource);
    if (readFile >= 0)
     return XLREAD_SUCCESS; /* success! */

    /*
     * Nope, not found in archive or pg_wal.
*/
    lastSourceFailed = true;
    break;

   case XLOG_FROM_STREAM:
    {
     bool  havedata;

     /*
      * We should be able to move to XLOG_FROM_STREAM only in
      * standby mode.
*/
     Assert(StandbyMode);

     /*
      * First, shutdown walreceiver if its restart has been
      * requested -- but no point if we're already slated for
      * starting it.
*/
     if (pendingWalRcvRestart && !startWalReceiver)
     {
      XLogShutdownWalRcv();

      /*
       * Re-scan for possible new timelines if we were
       * requested to recover to the latest timeline.
*/
      if (recoveryTargetTimeLineGoal ==
       RECOVERY_TARGET_TIMELINE_LATEST)
       rescanLatestTimeLine(replayTLI, replayLSN);

      startWalReceiver = true;
     }
     pendingWalRcvRestart = false;

     /*
      * Launch walreceiver if needed.
      *
      * If fetching_ckpt is true, RecPtr points to the initial
      * checkpoint location. In that case, we use RedoStartLSN
      * as the streaming start position instead of RecPtr, so
      * that when we later jump backwards to start redo at
      * RedoStartLSN, we will have the logs streamed already.
*/
     if (startWalReceiver &&
      PrimaryConnInfo && strcmp(PrimaryConnInfo, "") != 0)
     {
      XLogRecPtr ptr;
      TimeLineID tli;

      if (fetching_ckpt)
      {
       ptr = RedoStartLSN;
       tli = RedoStartTLI;
      }
      else
      {
       ptr = RecPtr;

       /*
        * Use the record begin position to determine the
        * TLI, rather than the position we're reading.
*/
       tli = tliOfPointInHistory(tliRecPtr, expectedTLEs);

       if (curFileTLI > 0 && tli < curFileTLI)
        elog(ERROR, "according to history file, WAL location %X/%X belongs to timeline %u, but previous recovered WAL file came from timeline %u",
          LSN_FORMAT_ARGS(tliRecPtr),
          tli, curFileTLI);
      }
      curFileTLI = tli;
      SetInstallXLogFileSegmentActive();
      RequestXLogStreaming(tli, ptr, PrimaryConnInfo,
            PrimarySlotName,
            wal_receiver_create_temp_slot);
      flushedUpto = 0;
     }

     /*
      * Check if WAL receiver is active or wait to start up.
*/
     if (!WalRcvStreaming())
     {
      lastSourceFailed = true;
      break;
     }

     /*
      * Walreceiver is active, so see if new data has arrived.
      *
      * We only advance XLogReceiptTime when we obtain fresh
      * WAL from walreceiver and observe that we had already
      * processed everything before the most recent "chunk"
      * that it flushed to disk.  In steady state where we are
      * keeping up with the incoming data, XLogReceiptTime will
      * be updated on each cycle. When we are behind,
      * XLogReceiptTime will not advance, so the grace time
      * allotted to conflicting queries will decrease.
*/
     if (RecPtr < flushedUpto)
      havedata = true;
     else
     {
      XLogRecPtr latestChunkStart;

      flushedUpto = GetWalRcvFlushRecPtr(&latestChunkStart, &receiveTLI);
      if (RecPtr < flushedUpto && receiveTLI == curFileTLI)
      {
       havedata = true;
       if (latestChunkStart <= RecPtr)
       {
        XLogReceiptTime = GetCurrentTimestamp();
        SetCurrentChunkStartTime(XLogReceiptTime);
       }
      }
      else
       havedata = false;
     }
     if (havedata)
     {
      /*
       * Great, streamed far enough.  Open the file if it's
       * not open already.  Also read the timeline history
       * file if we haven't initialized timeline history
       * yet; it should be streamed over and present in
       * pg_wal by now.  Use XLOG_FROM_STREAM so that source
       * info is set correctly and XLogReceiptTime isn't
       * changed.
       *
       * NB: We must set readTimeLineHistory based on
       * recoveryTargetTLI, not receiveTLI. Normally they'll
       * be the same, but if recovery_target_timeline is
       * 'latest' and archiving is configured, then it's
       * possible that we managed to retrieve one or more
       * new timeline history files from the archive,
       * updating recoveryTargetTLI.
*/
      if (readFile < 0)
      {
       if (!expectedTLEs)
        expectedTLEs = readTimeLineHistory(recoveryTargetTLI);
       readFile = XLogFileRead(readSegNo, receiveTLI,
             XLOG_FROM_STREAM, false);
       Assert(readFile >= 0);
      }
      else
      {
       /* just make sure source info is correct... */
       readSource = XLOG_FROM_STREAM;
       XLogReceiptSource = XLOG_FROM_STREAM;
       return XLREAD_SUCCESS;
      }
      break;
     }

     /* In nonblocking mode, return rather than sleeping. */
     if (nonblocking)
      return XLREAD_WOULDBLOCK;

     /*
      * Data not here yet. Check for trigger, then wait for
      * walreceiver to wake us up when new WAL arrives.
*/
     if (CheckForStandbyTrigger())
     {
      /*
       * Note that we don't return XLREAD_FAIL immediately
       * here. After being triggered, we still want to
       * replay all the WAL that was already streamed. It's
       * in pg_wal now, so we just treat this as a failure,
       * and the state machine will move on to replay the
       * streamed WAL from pg_wal, and then recheck the
       * trigger and exit replay.
*/
      lastSourceFailed = true;
      break;
     }

     /*
      * Since we have replayed everything we have received so
      * far and are about to start waiting for more WAL, let's
      * tell the upstream server our replay location now so
      * that pg_stat_replication doesn't show stale
      * information.
*/
     if (!streaming_reply_sent)
     {
      WalRcvForceReply();
      streaming_reply_sent = true;
     }

     /* Do any background tasks that might benefit us later. */
     KnownAssignedTransactionIdsIdleMaintenance();

     /* Update pg_stat_recovery_prefetch before sleeping. */
     XLogPrefetcherComputeStats(xlogprefetcher);

     /*
      * Wait for more WAL to arrive, when we will be woken
      * immediately by the WAL receiver.
*/
     (void) WaitLatch(&XLogRecoveryCtl->recoveryWakeupLatch,
          WL_LATCH_SET | WL_EXIT_ON_PM_DEATH,
          -1L,
          WAIT_EVENT_RECOVERY_WAL_STREAM);
     ResetLatch(&XLogRecoveryCtl->recoveryWakeupLatch);
     break;
    }

   default:
    elog(ERROR, "unexpected WAL source %d", currentSource);
  }

  /*
   * Check for recovery pause here so that we can confirm more quickly
   * that a requested pause has actually taken effect.
*/
  if (((volatile XLogRecoveryCtlData *) XLogRecoveryCtl)->recoveryPauseState !=
   RECOVERY_NOT_PAUSED)
   recoveryPausesHere(false);

  /*
   * This possibly-long loop needs to handle interrupts of startup
   * process.
*/
  ProcessStartupProcInterrupts();
}

return XLREAD_FAIL;   /* not reached */
}

/*
* Determine what log level should be used to report a corrupt WAL record
* in the current WAL page, previously read by XLogPageRead().
*
* 'emode' is the error mode that would be used to report a file-not-found
* or legitimate end-of-WAL situation.   Generally, we use it as-is, but if
* we're retrying the exact same record that we've tried previously, only
* complain the first time to keep the noise down.  However, we only do when
* reading from pg_wal, because we don't expect any invalid records in archive
* or in records streamed from the primary. Files in the archive should be complete,
* and we should never hit the end of WAL because we stop and wait for more WAL
* to arrive before replaying it.
*
* NOTE: This function remembers the RecPtr value it was last called with,
* to suppress repeated messages about the same record. Only call this when
* you are about to ereport(), or you might cause a later message to be
* erroneously suppressed.
*/
static int
emode_for_corrupt_record(int emode, XLogRecPtr RecPtr)
{
static XLogRecPtr lastComplaint = 0;

if (readSource == XLOG_FROM_PG_WAL && emode == LOG)
{
  if (RecPtr == lastComplaint)
   emode = DEBUG1;
  else
   lastComplaint = RecPtr;
}
return emode;
}

/*
* Subroutine to try to fetch and validate a prior checkpoint record.
*/
static XLogRecord *
ReadCheckpointRecord(XLogPrefetcher *xlogprefetcher, XLogRecPtr RecPtr,
      TimeLineID replayTLI)
{
XLogRecord *record;
uint8  info;

Assert(xlogreader != NULL);

if (!XRecOffIsValid(RecPtr))
{
  ereport(LOG,
    (errmsg("invalid checkpoint location")));
  return NULL;
}

XLogPrefetcherBeginRead(xlogprefetcher, RecPtr);
record = ReadRecord(xlogprefetcher, LOG, true, replayTLI);

if (record == NULL)
{
  ereport(LOG,
    (errmsg("invalid checkpoint record")));
  return NULL;
}
if (record->xl_rmid != RM_XLOG_ID)
{
  ereport(LOG,
    (errmsg("invalid resource manager ID in checkpoint record")));
  return NULL;
}
info = record->xl_info & ~XLR_INFO_MASK;
if (info != XLOG_CHECKPOINT_SHUTDOWN &&
  info != XLOG_CHECKPOINT_ONLINE)
{
  ereport(LOG,
    (errmsg("invalid xl_info in checkpoint record")));
  return NULL;
}
if (record->xl_tot_len != SizeOfXLogRecord + SizeOfXLogRecordDataHeaderShort + sizeof(CheckPoint))
{
  ereport(LOG,
    (errmsg("invalid length of checkpoint record")));
  return NULL;
}
return record;
}

/*
* Scan for new timelines that might have appeared in the archive since we
* started recovery.
*
* If there are any, the function changes recovery target TLI to the latest
* one and returns 'true'.
*/
static bool
rescanLatestTimeLine(TimeLineID replayTLI, XLogRecPtr replayLSN)
{
List    *newExpectedTLEs;
bool  found;
ListCell   *cell;
TimeLineID newtarget;
TimeLineID oldtarget = recoveryTargetTLI;
TimeLineHistoryEntry *currentTle = NULL;

newtarget = findNewestTimeLine(recoveryTargetTLI);
if (newtarget == recoveryTargetTLI)
{
  /* No new timelines found */
  return false;
}

/*
  * Determine the list of expected TLIs for the new TLI
*/

newExpectedTLEs = readTimeLineHistory(newtarget);

/*
  * If the current timeline is not part of the history of the new timeline,
  * we cannot proceed to it.
*/
found = false;
foreach(cell, newExpectedTLEs)
{
  currentTle = (TimeLineHistoryEntry *) lfirst(cell);

  if (currentTle->tli == recoveryTargetTLI)
  {
   found = true;
   break;
  }
}
if (!found)
{
  ereport(LOG,
    (errmsg("new timeline %u is not a child of database system timeline %u",
      newtarget,
      replayTLI)));
  return false;
}

/*
  * The current timeline was found in the history file, but check that the
  * next timeline was forked off from it *after* the current recovery
  * location.
*/
if (currentTle->end < replayLSN)
{
  ereport(LOG,
    (errmsg("new timeline %u forked off current database system timeline %u before current recovery point %X/%X",
      newtarget,
      replayTLI,
      LSN_FORMAT_ARGS(replayLSN))));
  return false;
}

/* The new timeline history seems valid. Switch target */
recoveryTargetTLI = newtarget;
list_free_deep(expectedTLEs);
expectedTLEs = newExpectedTLEs;

/*
  * As in StartupXLOG(), try to ensure we have all the history files
  * between the old target and new target in pg_wal.
*/
restoreTimeLineHistoryFiles(oldtarget + 1, newtarget);

ereport(LOG,
   (errmsg("new target timeline is %u",
     recoveryTargetTLI)));

return true;
}

/*
* Open a logfile segment for reading (during recovery).
*
* If source == XLOG_FROM_ARCHIVE, the segment is retrieved from archive.
* Otherwise, it's assumed to be already available in pg_wal.
*/
static int
XLogFileRead(XLogSegNo segno, TimeLineID tli,
    XLogSource source, bool notfoundOk)
{
char  xlogfname[MAXFNAMELEN];
char  activitymsg[MAXFNAMELEN + 16];
char  path[MAXPGPATH];
int   fd;

XLogFileName(xlogfname, tli, segno, wal_segment_size);

switch (source)
{
  case XLOG_FROM_ARCHIVE:
   /* Report recovery progress in PS display */
   snprintf(activitymsg, sizeof(activitymsg), "waiting for %s",
      xlogfname);
   set_ps_display(activitymsg);

   if (!RestoreArchivedFile(path, xlogfname,
          "RECOVERYXLOG",
          wal_segment_size,
          InRedo))
    return -1;
   break;

  case XLOG_FROM_PG_WAL:
  case XLOG_FROM_STREAM:
   XLogFilePath(path, tli, segno, wal_segment_size);
   break;

  default:
   elog(ERROR, "invalid XLogFileRead source %d", source);
}

/*
  * If the segment was fetched from archival storage, replace the existing
  * xlog segment (if any) with the archival version.
*/
if (source == XLOG_FROM_ARCHIVE)
{
  Assert(!IsInstallXLogFileSegmentActive());
  KeepFileRestoredFromArchive(path, xlogfname);

  /*
   * Set path to point at the new file in pg_wal.
*/
  snprintf(path, MAXPGPATH, XLOGDIR "/%s", xlogfname);
}

fd = BasicOpenFile(path, O_RDONLY | PG_BINARY);
if (fd >= 0)
{
  /* Success! */
  curFileTLI = tli;

  /* Report recovery progress in PS display */
  snprintf(activitymsg, sizeof(activitymsg), "recovering %s",
     xlogfname);
  set_ps_display(activitymsg);

  /* Track source of data in assorted state variables */
  readSource = source;
  XLogReceiptSource = source;
  /* In FROM_STREAM case, caller tracks receipt time, not me */
  if (source != XLOG_FROM_STREAM)
   XLogReceiptTime = GetCurrentTimestamp();

  return fd;
}
if (errno != ENOENT || !notfoundOk) /* unexpected failure? */
  ereport(PANIC,
    (errcode_for_file_access(),
     errmsg("could not open file \"%s\": %m", path)));
return -1;
}

/*
* Open a logfile segment for reading (during recovery).
*
* This version searches for the segment with any TLI listed in expectedTLEs.
*/
static int
XLogFileReadAnyTLI(XLogSegNo segno, XLogSource source)
{
char  path[MAXPGPATH];
ListCell   *cell;
int   fd;
List    *tles;

/*
  * Loop looking for a suitable timeline ID: we might need to read any of
  * the timelines listed in expectedTLEs.
  *
  * We expect curFileTLI on entry to be the TLI of the preceding file in
  * sequence, or 0 if there was no predecessor.  We do not allow curFileTLI
  * to go backwards; this prevents us from picking up the wrong file when a
  * parent timeline extends to higher segment numbers than the child we
  * want to read.
  *
  * If we haven't read the timeline history file yet, read it now, so that
  * we know which TLIs to scan.  We don't save the list in expectedTLEs,
  * however, unless we actually find a valid segment.  That way if there is
  * neither a timeline history file nor a WAL segment in the archive, and
  * streaming replication is set up, we'll read the timeline history file
  * streamed from the primary when we start streaming, instead of
  * recovering with a dummy history generated here.
*/
if (expectedTLEs)
  tles = expectedTLEs;
else
  tles = readTimeLineHistory(recoveryTargetTLI);

foreach(cell, tles)
{
  TimeLineHistoryEntry *hent = (TimeLineHistoryEntry *) lfirst(cell);
  TimeLineID tli = hent->tli;

  if (tli < curFileTLI)
   break;    /* don't bother looking at too-old TLIs */

  /*
   * Skip scanning the timeline ID that the logfile segment to read
   * doesn't belong to
*/
  if (hent->begin != InvalidXLogRecPtr)
  {
   XLogSegNo beginseg = 0;

   XLByteToSeg(hent->begin, beginseg, wal_segment_size);

   /*
    * The logfile segment that doesn't belong to the timeline is
    * older or newer than the segment that the timeline started or
    * ended at, respectively. It's sufficient to check only the
    * starting segment of the timeline here. Since the timelines are
    * scanned in descending order in this loop, any segments newer
    * than the ending segment should belong to newer timeline and
    * have already been read before. So it's not necessary to check
    * the ending segment of the timeline here.
*/
   if (segno < beginseg)
    continue;
  }

  if (source == XLOG_FROM_ANY || source == XLOG_FROM_ARCHIVE)
  {
   fd = XLogFileRead(segno, tli, XLOG_FROM_ARCHIVE, true);
   if (fd != -1)
   {
    elog(DEBUG1, "got WAL segment from archive");
    if (!expectedTLEs)
     expectedTLEs = tles;
    return fd;
   }
  }

  if (source == XLOG_FROM_ANY || source == XLOG_FROM_PG_WAL)
  {
   fd = XLogFileRead(segno, tli, XLOG_FROM_PG_WAL, true);
   if (fd != -1)
   {
    if (!expectedTLEs)
     expectedTLEs = tles;
    return fd;
   }
  }
}

/* Couldn't find it.  For simplicity, complain about front timeline */
XLogFilePath(path, recoveryTargetTLI, segno, wal_segment_size);
errno = ENOENT;
ereport(DEBUG2,
   (errcode_for_file_access(),
    errmsg("could not open file \"%s\": %m", path)));
return -1;
}

/*
* Set flag to signal the walreceiver to restart.  (The startup process calls
* this on noticing a relevant configuration change.)
*/
void
StartupRequestWalReceiverRestart(void)
{
if (currentSource == XLOG_FROM_STREAM && WalRcvRunning())
{
  ereport(LOG,
    (errmsg("WAL receiver process shutdown requested")));

  pendingWalRcvRestart = true;
}
}

/*
* Has a standby promotion already been triggered?
*
* Unlike CheckForStandbyTrigger(), this works in any process
* that's connected to shared memory.
*/
bool
PromoteIsTriggered(void)
{
/*
  * We check shared state each time only until a standby promotion is
  * triggered. We can't trigger a promotion again, so there's no need to
  * keep checking after the shared variable has once been seen true.
*/
if (LocalPromoteIsTriggered)
  return true;

SpinLockAcquire(&XLogRecoveryCtl->info_lck);
LocalPromoteIsTriggered = XLogRecoveryCtl->SharedPromoteIsTriggered;
SpinLockRelease(&XLogRecoveryCtl->info_lck);

return LocalPromoteIsTriggered;
}

static void
SetPromoteIsTriggered(void)
{
SpinLockAcquire(&XLogRecoveryCtl->info_lck);
XLogRecoveryCtl->SharedPromoteIsTriggered = true;
SpinLockRelease(&XLogRecoveryCtl->info_lck);

/*
  * Mark the recovery pause state as 'not paused' because the paused state
  * ends and promotion continues if a promotion is triggered while recovery
  * is paused. Otherwise pg_get_wal_replay_pause_state() can mistakenly
  * return 'paused' while a promotion is ongoing.
*/
SetRecoveryPause(false);

LocalPromoteIsTriggered = true;
}

/*
* Check whether a promote request has arrived.
*/
static bool
CheckForStandbyTrigger(void)
{
if (LocalPromoteIsTriggered)
  return true;

if (IsPromoteSignaled() && CheckPromoteSignal())
{
  ereport(LOG, (errmsg("received promote request")));
  RemovePromoteSignalFiles();
  ResetPromoteSignaled();
  SetPromoteIsTriggered();
  return true;
}

return false;
}

/*
* Remove the files signaling a standby promotion request.
*/
void
RemovePromoteSignalFiles(void)
{
unlink(PROMOTE_SIGNAL_FILE);
}

/*
* Check to see if a promote request has arrived.
*/
bool
CheckPromoteSignal(void)
{
struct stat stat_buf;

if (stat(PROMOTE_SIGNAL_FILE, &stat_buf) == 0)
  return true;

return false;
}

/*
* Wake up startup process to replay newly arrived WAL, or to notice that
* failover has been requested.
*/
void
WakeupRecovery(void)
{
SetLatch(&XLogRecoveryCtl->recoveryWakeupLatch);
}

/*
* Schedule a walreceiver wakeup in the main recovery loop.
*/
void
XLogRequestWalReceiverReply(void)
{
doRequestWalReceiverReply = true;
}

/*
* Is HotStandby active yet? This is only important in special backends
* since normal backends won't ever be able to connect until this returns
* true. Postmaster knows this by way of signal, not via shared memory.
*
* Unlike testing standbyState, this works in any process that's connected to
* shared memory.  (And note that standbyState alone doesn't tell the truth
* anyway.)
*/
bool
HotStandbyActive(void)
{
/*
  * We check shared state each time only until Hot Standby is active. We
  * can't de-activate Hot Standby, so there's no need to keep checking
  * after the shared variable has once been seen true.
*/
if (LocalHotStandbyActive)
  return true;
else
{
  /* spinlock is essential on machines with weak memory ordering! */
  SpinLockAcquire(&XLogRecoveryCtl->info_lck);
  LocalHotStandbyActive = XLogRecoveryCtl->SharedHotStandbyActive;
  SpinLockRelease(&XLogRecoveryCtl->info_lck);

  return LocalHotStandbyActive;
}
}

/*
* Like HotStandbyActive(), but to be used only in WAL replay code,
* where we don't need to ask any other process what the state is.
*/
static bool
HotStandbyActiveInReplay(void)
{
Assert(AmStartupProcess() || !IsPostmasterEnvironment);
return LocalHotStandbyActive;
}

/*
* Get latest redo apply position.
*
* Exported to allow WALReceiver to read the pointer directly.
*/
XLogRecPtr
GetXLogReplayRecPtr(TimeLineID *replayTLI)
{
XLogRecPtr recptr;
TimeLineID tli;

SpinLockAcquire(&XLogRecoveryCtl->info_lck);
recptr = XLogRecoveryCtl->lastReplayedEndRecPtr;
tli = XLogRecoveryCtl->lastReplayedTLI;
SpinLockRelease(&XLogRecoveryCtl->info_lck);

if (replayTLI)
  *replayTLI = tli;
return recptr;
}

/*
* Get position of last applied, or the record being applied.
*
* This is different from GetXLogReplayRecPtr() in that if a WAL
* record is currently being applied, this includes that record.
*/
XLogRecPtr
GetCurrentReplayRecPtr(TimeLineID *replayEndTLI)
{
XLogRecPtr recptr;
TimeLineID tli;

SpinLockAcquire(&XLogRecoveryCtl->info_lck);
recptr = XLogRecoveryCtl->replayEndRecPtr;
tli = XLogRecoveryCtl->replayEndTLI;
SpinLockRelease(&XLogRecoveryCtl->info_lck);

if (replayEndTLI)
  *replayEndTLI = tli;
return recptr;
}

/*
* Save timestamp of latest processed commit/abort record.
*
* We keep this in XLogRecoveryCtl, not a simple static variable, so that it can be
* seen by processes other than the startup process.  Note in particular
* that CreateRestartPoint is executed in the checkpointer.
*/
static void
SetLatestXTime(TimestampTz xtime)
{
SpinLockAcquire(&XLogRecoveryCtl->info_lck);
XLogRecoveryCtl->recoveryLastXTime = xtime;
SpinLockRelease(&XLogRecoveryCtl->info_lck);
}

/*
* Fetch timestamp of latest processed commit/abort record.
*/
TimestampTz
GetLatestXTime(void)
{
TimestampTz xtime;

SpinLockAcquire(&XLogRecoveryCtl->info_lck);
xtime = XLogRecoveryCtl->recoveryLastXTime;
SpinLockRelease(&XLogRecoveryCtl->info_lck);

return xtime;
}

/*
* Save timestamp of the next chunk of WAL records to apply.
*
* We keep this in XLogRecoveryCtl, not a simple static variable, so that it can be
* seen by all backends.
*/
static void
SetCurrentChunkStartTime(TimestampTz xtime)
{
SpinLockAcquire(&XLogRecoveryCtl->info_lck);
XLogRecoveryCtl->currentChunkStartTime = xtime;
SpinLockRelease(&XLogRecoveryCtl->info_lck);
}

/*
* Fetch timestamp of latest processed commit/abort record.
* Startup process maintains an accurate local copy in XLogReceiptTime
*/
TimestampTz
GetCurrentChunkReplayStartTime(void)
{
TimestampTz xtime;

SpinLockAcquire(&XLogRecoveryCtl->info_lck);
xtime = XLogRecoveryCtl->currentChunkStartTime;
SpinLockRelease(&XLogRecoveryCtl->info_lck);

return xtime;
}

/*
* Returns time of receipt of current chunk of XLOG data, as well as
* whether it was received from streaming replication or from archives.
*/
void
GetXLogReceiptTime(TimestampTz *rtime, bool *fromStream)
{
/*
  * This must be executed in the startup process, since we don't export the
  * relevant state to shared memory.
*/
Assert(InRecovery);

*rtime = XLogReceiptTime;
*fromStream = (XLogReceiptSource == XLOG_FROM_STREAM);
}

/*
* Note that text field supplied is a parameter name and does not require
* translation
*/
void
RecoveryRequiresIntParameter(const char *param_name, int currValue, int minValue)
{
if (currValue < minValue)
{
  if (HotStandbyActiveInReplay())
  {
   bool  warned_for_promote = false;

   ereport(WARNING,
     (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
      errmsg("hot standby is not possible because of insufficient parameter settings"),
      errdetail("%s = %d is a lower setting than on the primary server, where its value was %d.",
          param_name,
          currValue,
          minValue)));

   SetRecoveryPause(true);

   ereport(LOG,
     (errmsg("recovery has paused"),
      errdetail("If recovery is unpaused, the server will shut down."),
      errhint("You can then restart the server after making the necessary configuration changes.")));

   while (GetRecoveryPauseState() != RECOVERY_NOT_PAUSED)
   {
    ProcessStartupProcInterrupts();

    if (CheckForStandbyTrigger())
    {
     if (!warned_for_promote)
      ereport(WARNING,
        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
         errmsg("promotion is not possible because of insufficient parameter settings"),

      /*
       * Repeat the detail from above so it's easy to find
       * in the log.
*/
         errdetail("%s = %d is a lower setting than on the primary server, where its value was %d.",
             param_name,
             currValue,
             minValue),
         errhint("Restart the server after making the necessary configuration changes.")));
     warned_for_promote = true;
    }

    /*
     * If recovery pause is requested then set it paused.  While
     * we are in the loop, user might resume and pause again so
     * set this every time.
*/
    ConfirmRecoveryPaused();

    /*
     * We wait on a condition variable that will wake us as soon
     * as the pause ends, but we use a timeout so we can check the
     * above conditions periodically too.
*/
    ConditionVariableTimedSleep(&XLogRecoveryCtl->recoveryNotPausedCV, 1000,
           WAIT_EVENT_RECOVERY_PAUSE);
   }
   ConditionVariableCancelSleep();
  }

  ereport(FATAL,
    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
     errmsg("recovery aborted because of insufficient parameter settings"),
  /* Repeat the detail from above so it's easy to find in the log. */
     errdetail("%s = %d is a lower setting than on the primary server, where its value was %d.",
         param_name,
         currValue,
         minValue),
     errhint("You can restart the server after making the necessary configuration changes.")));
}
}

/*
* GUC check_hook for primary_slot_name
*/
bool
check_primary_slot_name(char **newval, void **extra, GucSource source)
{
int   err_code;
char    *err_msg = NULL;
char    *err_hint = NULL;

if (*newval && strcmp(*newval, "") != 0 &&
  !ReplicationSlotValidateNameInternal(*newval, &err_code, &err_msg,
            &err_hint))
{
  GUC_check_errcode(err_code);
  GUC_check_errdetail("%s", err_msg);
  if (err_hint != NULL)
   GUC_check_errhint("%s", err_hint);
  return false;
}

return true;
}

/*
* Recovery target settings: Only one of the several recovery_target* settings
* may be set.  Setting a second one results in an error.  The global variable
* recoveryTarget tracks which kind of recovery target was chosen.  Other
* variables store the actual target value (for example a string or a xid).
* The assign functions of the parameters check whether a competing parameter
* was already set.  But we want to allow setting the same parameter multiple
* times.  We also want to allow unsetting a parameter and setting a different
* one, so we unset recoveryTarget when the parameter is set to an empty
* string.
*
* XXX this code is broken by design.  Throwing an error from a GUC assign
* hook breaks fundamental assumptions of guc.c.  So long as all the variables
* for which this can happen are PGC_POSTMASTER, the consequences are limited,
* since we'd just abort postmaster startup anyway.  Nonetheless it's likely
* that we have odd behaviors such as unexpected GUC ordering dependencies.
*/

pg_noreturn static void
error_multiple_recovery_targets(void)
{
ereport(ERROR,
   (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
    errmsg("multiple recovery targets specified"),
    errdetail("At most one of \"recovery_target\", \"recovery_target_lsn\", \"recovery_target_name\", \"recovery_target_time\", \"recovery_target_xid\" may be set.")));
}

/*
* GUC check_hook for recovery_target
*/
bool
check_recovery_target(char **newval, void **extra, GucSource source)
{
if (strcmp(*newval, "immediate") != 0 && strcmp(*newval, "") != 0)
{
  GUC_check_errdetail("The only allowed value is \"immediate\".");
  return false;
}
return true;
}

/*
* GUC assign_hook for recovery_target
*/
void
assign_recovery_target(const char *newval, void *extra)
{
if (recoveryTarget != RECOVERY_TARGET_UNSET &&
  recoveryTarget != RECOVERY_TARGET_IMMEDIATE)
  error_multiple_recovery_targets();

if (newval && strcmp(newval, "") != 0)
  recoveryTarget = RECOVERY_TARGET_IMMEDIATE;
else
  recoveryTarget = RECOVERY_TARGET_UNSET;
}

/*
* GUC check_hook for recovery_target_lsn
*/
bool
check_recovery_target_lsn(char **newval, void **extra, GucSource source)
{
if (strcmp(*newval, "") != 0)
{
  XLogRecPtr lsn;
  XLogRecPtr *myextra;
  bool  have_error = false;

  lsn = pg_lsn_in_internal(*newval, &have_error);
  if (have_error)
   return false;

  myextra = (XLogRecPtr *) guc_malloc(LOG, sizeof(XLogRecPtr));
  if (!myextra)
   return false;
  *myextra = lsn;
  *extra = myextra;
}
return true;
}

/*
* GUC assign_hook for recovery_target_lsn
*/
void
assign_recovery_target_lsn(const char *newval, void *extra)
{
if (recoveryTarget != RECOVERY_TARGET_UNSET &&
  recoveryTarget != RECOVERY_TARGET_LSN)
  error_multiple_recovery_targets();

if (newval && strcmp(newval, "") != 0)
{
  recoveryTarget = RECOVERY_TARGET_LSN;
  recoveryTargetLSN = *((XLogRecPtr *) extra);
}
else
  recoveryTarget = RECOVERY_TARGET_UNSET;
}

/*
* GUC check_hook for recovery_target_name
*/
bool
check_recovery_target_name(char **newval, void **extra, GucSource source)
{
/* Use the value of newval directly */
if (strlen(*newval) >= MAXFNAMELEN)
{
  GUC_check_errdetail("\"%s\" is too long (maximum %d characters).",
       "recovery_target_name", MAXFNAMELEN - 1);
  return false;
}
return true;
}

/*
* GUC assign_hook for recovery_target_name
*/
void
assign_recovery_target_name(const char *newval, void *extra)
{
if (recoveryTarget != RECOVERY_TARGET_UNSET &&
  recoveryTarget != RECOVERY_TARGET_NAME)
  error_multiple_recovery_targets();

if (newval && strcmp(newval, "") != 0)
{
  recoveryTarget = RECOVERY_TARGET_NAME;
  recoveryTargetName = newval;
}
else
  recoveryTarget = RECOVERY_TARGET_UNSET;
}

/*
* GUC check_hook for recovery_target_time
*
* The interpretation of the recovery_target_time string can depend on the
* time zone setting, so we need to wait until after all GUC processing is
* done before we can do the final parsing of the string.  This check function
* only does a parsing pass to catch syntax errors, but we store the string
* and parse it again when we need to use it.
*/
bool
check_recovery_target_time(char **newval, void **extra, GucSource source)
{
if (strcmp(*newval, "") != 0)
{
  /* reject some special values */
  if (strcmp(*newval, "now") == 0 ||
   strcmp(*newval, "today") == 0 ||
   strcmp(*newval, "tomorrow") == 0 ||
   strcmp(*newval, "yesterday") == 0)
  {
   return false;
  }

  /*
   * parse timestamp value (see also timestamptz_in())
*/
  {
   char    *str = *newval;
   fsec_t  fsec;
   struct pg_tm tt,
        *tm = &tt;
   int   tz;
   int   dtype;
   int   nf;
   int   dterr;
   char    *field[MAXDATEFIELDS];
   int   ftype[MAXDATEFIELDS];
   char  workbuf[MAXDATELEN + MAXDATEFIELDS];
   DateTimeErrorExtra dtextra;
   TimestampTz timestamp;

   dterr = ParseDateTime(str, workbuf, sizeof(workbuf),
          field, ftype, MAXDATEFIELDS, &nf);
   if (dterr == 0)
    dterr = DecodeDateTime(field, ftype, nf,
            &dtype, tm, &fsec, &tz, &dtextra);
   if (dterr != 0)
    return false;
   if (dtype != DTK_DATE)
    return false;

   if (tm2timestamp(tm, fsec, &tz, ×tamp) != 0)
   {
    GUC_check_errdetail("Timestamp out of range: \"%s\".", str);
    return false;
   }
  }
}
return true;
}

/*
* GUC assign_hook for recovery_target_time
*/
void
assign_recovery_target_time(const char *newval, void *extra)
{
if (recoveryTarget != RECOVERY_TARGET_UNSET &&
  recoveryTarget != RECOVERY_TARGET_TIME)
  error_multiple_recovery_targets();

if (newval && strcmp(newval, "") != 0)
  recoveryTarget = RECOVERY_TARGET_TIME;
else
  recoveryTarget = RECOVERY_TARGET_UNSET;
}

/*
* GUC check_hook for recovery_target_timeline
*/
bool
check_recovery_target_timeline(char **newval, void **extra, GucSource source)
{
RecoveryTargetTimeLineGoal rttg;
RecoveryTargetTimeLineGoal *myextra;

if (strcmp(*newval, "current") == 0)
  rttg = RECOVERY_TARGET_TIMELINE_CONTROLFILE;
else if (strcmp(*newval, "latest") == 0)
  rttg = RECOVERY_TARGET_TIMELINE_LATEST;
else
{
  rttg = RECOVERY_TARGET_TIMELINE_NUMERIC;

  errno = 0;
  strtoul(*newval, NULL, 0);
  if (errno == EINVAL || errno == ERANGE)
  {
   GUC_check_errdetail("\"recovery_target_timeline\" is not a valid number.");
   return false;
  }
}

myextra = (RecoveryTargetTimeLineGoal *) guc_malloc(LOG, sizeof(RecoveryTargetTimeLineGoal));
if (!myextra)
  return false;
*myextra = rttg;
*extra = myextra;

return true;
}

/*
* GUC assign_hook for recovery_target_timeline
*/
void
assign_recovery_target_timeline(const char *newval, void *extra)
{
recoveryTargetTimeLineGoal = *((RecoveryTargetTimeLineGoal *) extra);
if (recoveryTargetTimeLineGoal == RECOVERY_TARGET_TIMELINE_NUMERIC)
  recoveryTargetTLIRequested = (TimeLineID) strtoul(newval, NULL, 0);
else
  recoveryTargetTLIRequested = 0;
}

/*
* GUC check_hook for recovery_target_xid
*/
bool
check_recovery_target_xid(char **newval, void **extra, GucSource source)
{
if (strcmp(*newval, "") != 0)
{
  TransactionId xid;
  TransactionId *myextra;

  errno = 0;
  xid = (TransactionId) strtou64(*newval, NULL, 0);
  if (errno == EINVAL || errno == ERANGE)
   return false;

  myextra = (TransactionId *) guc_malloc(LOG, sizeof(TransactionId));
  if (!myextra)
   return false;
  *myextra = xid;
  *extra = myextra;
}
return true;
}

/*
* GUC assign_hook for recovery_target_xid
*/
void
assign_recovery_target_xid(const char *newval, void *extra)
{
if (recoveryTarget != RECOVERY_TARGET_UNSET &&
  recoveryTarget != RECOVERY_TARGET_XID)
  error_multiple_recovery_targets();

if (newval && strcmp(newval, "") != 0)
{
  recoveryTarget = RECOVERY_TARGET_XID;
  recoveryTargetXid = *((TransactionId *) extra);
}
else
  recoveryTarget = RECOVERY_TARGET_UNSET;
}

Messung V0.5 in Prozent

Quelle xlogrecovery.c Sprache: unbekannt

[Dauer der Verarbeitung: 1.744 Sekunden, vorverarbeitet 2026-09-28]