xlog.h

Go to the documentation of this file.

/*
 * xlog.h
 *
 * PostgreSQL write-ahead log manager
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/access/xlog.h
 */
#ifndef XLOG_H
#define XLOG_H
 
#include "access/xlogbackup.h"
#include "access/xlogdefs.h"
#include "replication/logicalctl.h"
#include "datatype/timestamp.h"
#include "lib/stringinfo.h"
#include "nodes/pg_list.h"
 
 
/* Sync methods */
enum WalSyncMethod
{
    WAL_SYNC_METHOD_FSYNC = 0,
    WAL_SYNC_METHOD_FDATASYNC,
    WAL_SYNC_METHOD_OPEN,       /* for O_SYNC */
    WAL_SYNC_METHOD_FSYNC_WRITETHROUGH,
    WAL_SYNC_METHOD_OPEN_DSYNC  /* for O_DSYNC */
};
extern PGDLLIMPORT int wal_sync_method;
 
extern PGDLLIMPORT XLogRecPtr ProcLastRecPtr;
extern PGDLLIMPORT XLogRecPtr XactLastRecEnd;
extern PGDLLIMPORT XLogRecPtr XactLastCommitEnd;
 
/* these variables are GUC parameters related to XLOG */
extern PGDLLIMPORT int wal_segment_size;
extern PGDLLIMPORT int min_wal_size_mb;
extern PGDLLIMPORT int max_wal_size_mb;
extern PGDLLIMPORT int wal_keep_size_mb;
extern PGDLLIMPORT int max_slot_wal_keep_size_mb;
extern PGDLLIMPORT int XLOGbuffers;
extern PGDLLIMPORT int XLogArchiveTimeout;
extern PGDLLIMPORT int wal_retrieve_retry_interval;
extern PGDLLIMPORT char *XLogArchiveCommand;
extern PGDLLIMPORT bool EnableHotStandby;
extern PGDLLIMPORT bool fullPageWrites;
extern PGDLLIMPORT bool wal_log_hints;
extern PGDLLIMPORT int wal_compression;
extern PGDLLIMPORT bool wal_init_zero;
extern PGDLLIMPORT bool wal_recycle;
extern PGDLLIMPORT bool *wal_consistency_checking;
extern PGDLLIMPORT char *wal_consistency_checking_string;
extern PGDLLIMPORT bool log_checkpoints;
extern PGDLLIMPORT int CommitDelay;
extern PGDLLIMPORT int CommitSiblings;
extern PGDLLIMPORT bool track_wal_io_timing;
extern PGDLLIMPORT int wal_decode_buffer_size;
extern PGDLLIMPORT int data_checksums;
 
extern PGDLLIMPORT int CheckPointSegments;
 
/* Archive modes */
typedef enum ArchiveMode
{
    ARCHIVE_MODE_OFF = 0,       /* disabled */
    ARCHIVE_MODE_ON,            /* enabled while server is running normally */
    ARCHIVE_MODE_ALWAYS,        /* enabled always (even during recovery) */
} ArchiveMode;
extern PGDLLIMPORT int XLogArchiveMode;
 
/* WAL levels */
typedef enum WalLevel
{
    WAL_LEVEL_MINIMAL = 0,
    WAL_LEVEL_REPLICA,
    WAL_LEVEL_LOGICAL,
} WalLevel;
 
/* Compression algorithms for WAL */
typedef enum WalCompression
{
    WAL_COMPRESSION_NONE = 0,
    WAL_COMPRESSION_PGLZ,
    WAL_COMPRESSION_LZ4,
    WAL_COMPRESSION_ZSTD,
} WalCompression;
 
/* Recovery states */
typedef enum RecoveryState
{
    RECOVERY_STATE_CRASH = 0,   /* crash recovery */
    RECOVERY_STATE_ARCHIVE,     /* archive recovery */
    RECOVERY_STATE_DONE,        /* currently in production */
} RecoveryState;
 
extern PGDLLIMPORT int wal_level;
extern PGDLLIMPORT bool XLogLogicalInfo;
 
/* Is WAL archiving enabled (always or only while server is running normally)? */
#define XLogArchivingActive() \
    (AssertMacro(XLogArchiveMode == ARCHIVE_MODE_OFF || wal_level >= WAL_LEVEL_REPLICA), XLogArchiveMode > ARCHIVE_MODE_OFF)
/* Is WAL archiving enabled always (even during recovery)? */
#define XLogArchivingAlways() \
    (AssertMacro(XLogArchiveMode == ARCHIVE_MODE_OFF || wal_level >= WAL_LEVEL_REPLICA), XLogArchiveMode == ARCHIVE_MODE_ALWAYS)
 
/*
 * Is WAL-logging necessary for archival or log-shipping, or can we skip
 * WAL-logging if we fsync() the data before committing instead?
 */
#define XLogIsNeeded() (wal_level >= WAL_LEVEL_REPLICA)
 
/*
 * Is a full-page image needed for hint bit updates?
 *
 * Normally, we don't WAL-log hint bit updates, but if checksums are enabled,
 * we have to protect them against torn page writes.  When you only set
 * individual bits on a page, it's still consistent no matter what combination
 * of the bits make it to disk, but the checksum wouldn't match.  Also WAL-log
 * them if forced by wal_log_hints=on.
 */
#define XLogHintBitIsNeeded() (wal_log_hints || DataChecksumsNeedWrite())
 
/* Do we need to WAL-log information required only for Hot Standby and logical replication? */
#define XLogStandbyInfoActive() (wal_level >= WAL_LEVEL_REPLICA)
 
/*
 * Do we need to WAL-log information required only for logical replication?
 *
 * When XLogLogicalInfoActive() returns true, it enables logical-decoding-related
 * WAL logging as if wal_level were set to 'logical', even if it's actually set
 * to 'replica'. Note that XLogLogicalInfo is a process-local cache and can
 * change until an XID is assigned to the transaction. In other words, it
 * ensures that the same result is returned within an XID-assigned transaction.
 */
#define XLogLogicalInfoActive() \
     (wal_level >= WAL_LEVEL_LOGICAL || XLogLogicalInfo)
 
#ifdef WAL_DEBUG
extern PGDLLIMPORT bool XLOG_DEBUG;
#endif
 
/*
 * OR-able request flag bits for checkpoints.  The "cause" bits are used only
 * for logging purposes.  Note: the flags must be defined so that it's
 * sensible to OR together request flags arising from different requestors.
 */
 
/* These directly affect the behavior of CreateCheckPoint and subsidiaries */
#define CHECKPOINT_IS_SHUTDOWN  0x0001  /* Checkpoint is for shutdown */
#define CHECKPOINT_END_OF_RECOVERY  0x0002  /* Like shutdown checkpoint, but
                                             * issued at end of WAL recovery */
#define CHECKPOINT_FAST         0x0004  /* Do it without delays */
#define CHECKPOINT_FORCE        0x0008  /* Force even if no activity */
#define CHECKPOINT_FLUSH_UNLOGGED   0x0010  /* Flush unlogged tables */
/* These are important to RequestCheckpoint */
#define CHECKPOINT_WAIT         0x0020  /* Wait for completion */
#define CHECKPOINT_REQUESTED    0x0040  /* Checkpoint request has been made */
/* These indicate the cause of a checkpoint request */
#define CHECKPOINT_CAUSE_XLOG   0x0080  /* XLOG consumption */
#define CHECKPOINT_CAUSE_TIME   0x0100  /* Elapsed time */
 
/*
 * Flag bits for the record being inserted, set using XLogSetRecordFlags().
 */
#define XLOG_INCLUDE_ORIGIN     0x01    /* include the replication origin */
#define XLOG_MARK_UNIMPORTANT   0x02    /* record not important for durability */
 
 
/* Checkpoint statistics */
typedef struct CheckpointStatsData
{
    TimestampTz ckpt_start_t;   /* start of checkpoint */
    TimestampTz ckpt_write_t;   /* start of flushing buffers */
    TimestampTz ckpt_sync_t;    /* start of fsyncs */
    TimestampTz ckpt_sync_end_t;    /* end of fsyncs */
    TimestampTz ckpt_end_t;     /* end of checkpoint */
 
    int         ckpt_bufs_written;  /* # of buffers written */
    int         ckpt_slru_written;  /* # of SLRU buffers written */
 
    int         ckpt_segs_added;    /* # of new xlog segments created */
    int         ckpt_segs_removed;  /* # of xlog segments deleted */
    int         ckpt_segs_recycled; /* # of xlog segments recycled */
 
    int         ckpt_sync_rels; /* # of relations synced */
    uint64      ckpt_longest_sync;  /* Longest sync for one relation */
    uint64      ckpt_agg_sync_time; /* The sum of all the individual sync
                                     * times, which is not necessarily the
                                     * same as the total elapsed time for the
                                     * entire sync phase. */
} CheckpointStatsData;
 
extern PGDLLIMPORT CheckpointStatsData CheckpointStats;
 
/*
 * GetWALAvailability return codes
 */
typedef enum WALAvailability
{
    WALAVAIL_INVALID_LSN,       /* parameter error */
    WALAVAIL_RESERVED,          /* WAL segment is within max_wal_size */
    WALAVAIL_EXTENDED,          /* WAL segment is reserved by a slot or
                                 * wal_keep_size */
    WALAVAIL_UNRESERVED,        /* no longer reserved, but not removed yet */
    WALAVAIL_REMOVED,           /* WAL segment has been removed */
} WALAvailability;
 
struct XLogRecData;
struct XLogReaderState;
 
extern XLogRecPtr XLogInsertRecord(struct XLogRecData *rdata,
                                   XLogRecPtr fpw_lsn,
                                   uint8 flags,
                                   int num_fpi,
                                   uint64 fpi_bytes,
                                   bool topxid_included);
extern void XLogFlush(XLogRecPtr record);
extern bool XLogBackgroundFlush(void);
extern bool XLogNeedsFlush(XLogRecPtr record);
extern int  XLogFileInit(XLogSegNo logsegno, TimeLineID logtli);
extern int  XLogFileOpen(XLogSegNo segno, TimeLineID tli);
 
extern void CheckXLogRemoved(XLogSegNo segno, TimeLineID tli);
extern XLogSegNo XLogGetLastRemovedSegno(void);
extern XLogSegNo XLogGetOldestSegno(TimeLineID tli);
extern void XLogSetAsyncXactLSN(XLogRecPtr asyncXactLSN);
extern void XLogSetReplicationSlotMinimumLSN(XLogRecPtr lsn);
extern XLogRecPtr XLogGetReplicationSlotMinimumLSN(void);
 
extern void xlog_redo(struct XLogReaderState *record);
extern void xlog2_redo(struct XLogReaderState *record);
extern void xlog_desc(StringInfo buf, struct XLogReaderState *record);
extern void xlog2_desc(StringInfo buf, struct XLogReaderState *record);
extern const char *xlog_identify(uint8 info);
extern const char *xlog2_identify(uint8 info);
 
extern void issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli);
 
extern bool RecoveryInProgress(void);
extern RecoveryState GetRecoveryState(void);
extern bool XLogInsertAllowed(void);
extern XLogRecPtr GetXLogInsertRecPtr(void);
extern XLogRecPtr GetXLogInsertEndRecPtr(void);
extern XLogRecPtr GetXLogWriteRecPtr(void);
 
extern uint64 GetSystemIdentifier(void);
extern char *GetMockAuthenticationNonce(void);
extern bool DataChecksumsNeedWrite(void);
extern bool DataChecksumsNeedVerify(void);
extern bool DataChecksumsInProgressOn(void);
extern void SetDataChecksumsOnInProgress(void);
extern void SetDataChecksumsOn(void);
extern void SetDataChecksumsOff(void);
extern const char *show_data_checksums(void);
extern const char *get_checksum_state_string(uint32 state);
extern void InitLocalDataChecksumState(void);
extern void SetLocalDataChecksumState(uint32 data_checksum_version);
extern bool GetDefaultCharSignedness(void);
extern XLogRecPtr GetFakeLSNForUnloggedRel(void);
extern void BootStrapXLOG(uint32 data_checksum_version);
extern void InitializeWalConsistencyChecking(void);
extern void LocalProcessControlFile(bool reset);
extern WalLevel GetActiveWalLevelOnStandby(void);
extern void StartupXLOG(void);
extern void ShutdownXLOG(int code, Datum arg);
extern bool CreateCheckPoint(int flags);
extern bool CreateRestartPoint(int flags);
extern WALAvailability GetWALAvailability(XLogRecPtr targetLSN);
extern void XLogPutNextOid(Oid nextOid);
extern XLogRecPtr XLogRestorePoint(const char *rpName);
extern XLogRecPtr XLogAssignLSN(void);
extern void UpdateFullPageWrites(void);
extern void GetFullPageWriteInfo(XLogRecPtr *RedoRecPtr_p, bool *doPageWrites_p);
extern XLogRecPtr GetRedoRecPtr(void);
extern XLogRecPtr GetInsertRecPtr(void);
extern XLogRecPtr GetFlushRecPtr(TimeLineID *insertTLI);
extern TimeLineID GetWALInsertionTimeLine(void);
extern TimeLineID GetWALInsertionTimeLineIfSet(void);
extern XLogRecPtr GetLastImportantRecPtr(void);
 
extern void SetWalWriterSleeping(bool sleeping);
 
extern void WakeupCheckpointer(void);
 
extern Size WALReadFromBuffers(char *dstbuf, XLogRecPtr startptr, Size count,
                               TimeLineID tli);
 
/*
 * Routines used by xlogrecovery.c to call back into xlog.c during recovery.
 */
extern void RemoveNonParentXlogFiles(XLogRecPtr switchpoint, TimeLineID newTLI);
extern bool XLogCheckpointNeeded(XLogSegNo new_segno);
extern void SwitchIntoArchiveRecovery(XLogRecPtr EndRecPtr, TimeLineID replayTLI);
extern void ReachedEndOfBackup(XLogRecPtr EndRecPtr, TimeLineID tli);
extern void SetInstallXLogFileSegmentActive(void);
extern bool IsInstallXLogFileSegmentActive(void);
extern void ResetInstallXLogFileSegmentActive(void);
extern void XLogShutdownWalRcv(void);
 
/*
 * Routines to start, stop, and get status of a base backup.
 */
 
/*
 * Session-level status of base backups
 *
 * This is used in parallel with the shared memory status to control parallel
 * execution of base backup functions for a given session, be it a backend
 * dedicated to replication or a normal backend connected to a database. The
 * update of the session-level status happens at the same time as the shared
 * memory counters to keep a consistent global and local state of the backups
 * running.
 */
typedef enum SessionBackupState
{
    SESSION_BACKUP_NONE,
    SESSION_BACKUP_RUNNING,
} SessionBackupState;
 
extern void do_pg_backup_start(const char *backupidstr, bool fast,
                               List **tablespaces, BackupState *state,
                               StringInfo tblspcmapfile);
extern void do_pg_backup_stop(BackupState *state, bool waitforarchive);
extern void do_pg_abort_backup(int code, Datum arg);
extern void register_persistent_abort_backup_handler(void);
extern SessionBackupState get_backup_status(void);
 
/* File path names (all relative to $PGDATA) */
#define RECOVERY_SIGNAL_FILE    "recovery.signal"
#define STANDBY_SIGNAL_FILE     "standby.signal"
#define BACKUP_LABEL_FILE       "backup_label"
#define BACKUP_LABEL_OLD        "backup_label.old"
 
#define TABLESPACE_MAP          "tablespace_map"
#define TABLESPACE_MAP_OLD      "tablespace_map.old"
 
/* files to signal promotion to primary */
#define PROMOTE_SIGNAL_FILE     "promote"
 
#endif                          /* XLOG_H */