xlog_internal.h

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/*
 * xlog_internal.h
 *
 * PostgreSQL write-ahead log internal declarations
 *
 * NOTE: this file is intended to contain declarations useful for
 * manipulating the XLOG files directly, but it is not supposed to be
 * needed by rmgr routines (redo support for individual record types).
 * So the XLogRecord typedef and associated stuff appear in xlogrecord.h.
 *
 * Note: This file must be includable in both frontend and backend contexts,
 * to allow stand-alone tools like pg_receivewal to deal with WAL files.
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/access/xlog_internal.h
 */
#ifndef XLOG_INTERNAL_H
#define XLOG_INTERNAL_H
 
#include "access/xlogdefs.h"
#include "access/xlogreader.h"
#include "datatype/timestamp.h"
#include "lib/stringinfo.h"
#include "pgtime.h"
#include "storage/block.h"
#include "storage/relfilelocator.h"
 
 
/*
 * Each page of XLOG file has a header like this:
 */
#define XLOG_PAGE_MAGIC 0xD11C  /* can be used as WAL version indicator */
 
typedef struct XLogPageHeaderData
{
    uint16      xlp_magic;      /* magic value for correctness checks */
    uint16      xlp_info;       /* flag bits, see below */
    TimeLineID  xlp_tli;        /* TimeLineID of first record on page */
    XLogRecPtr  xlp_pageaddr;   /* XLOG address of this page */
 
    /*
     * When there is not enough space on current page for whole record, we
     * continue on the next page.  xlp_rem_len is the number of bytes
     * remaining from a previous page; it tracks xl_tot_len in the initial
     * header.  Note that the continuation data isn't necessarily aligned.
     */
    uint32      xlp_rem_len;    /* total len of remaining data for record */
} XLogPageHeaderData;
 
#define SizeOfXLogShortPHD  MAXALIGN(sizeof(XLogPageHeaderData))
 
typedef XLogPageHeaderData *XLogPageHeader;
 
/*
 * When the XLP_LONG_HEADER flag is set, we store additional fields in the
 * page header.  (This is ordinarily done just in the first page of an
 * XLOG file.)  The additional fields serve to identify the file accurately.
 */
typedef struct XLogLongPageHeaderData
{
    XLogPageHeaderData std;     /* standard header fields */
    uint64      xlp_sysid;      /* system identifier from pg_control */
    uint32      xlp_seg_size;   /* just as a cross-check */
    uint32      xlp_xlog_blcksz;    /* just as a cross-check */
} XLogLongPageHeaderData;
 
#define SizeOfXLogLongPHD   MAXALIGN(sizeof(XLogLongPageHeaderData))
 
typedef XLogLongPageHeaderData *XLogLongPageHeader;
 
/* When record crosses page boundary, set this flag in new page's header */
#define XLP_FIRST_IS_CONTRECORD     0x0001
/* This flag indicates a "long" page header */
#define XLP_LONG_HEADER             0x0002
/* Replaces a missing contrecord; see CreateOverwriteContrecordRecord */
#define XLP_FIRST_IS_OVERWRITE_CONTRECORD 0x0004
/* All defined flag bits in xlp_info (used for validity checking of header) */
#define XLP_ALL_FLAGS               0x0007
 
#define XLogPageHeaderSize(hdr)     \
    (((hdr)->xlp_info & XLP_LONG_HEADER) ? SizeOfXLogLongPHD : SizeOfXLogShortPHD)
 
/* wal_segment_size can range from 1MB to 1GB */
#define WalSegMinSize 1024 * 1024
#define WalSegMaxSize 1024 * 1024 * 1024
/* default number of min and max wal segments */
#define DEFAULT_MIN_WAL_SEGS 5
#define DEFAULT_MAX_WAL_SEGS 64
 
/* check that the given size is a valid wal_segment_size */
#define IsPowerOf2(x) (x > 0 && ((x) & ((x)-1)) == 0)
#define IsValidWalSegSize(size) \
     (IsPowerOf2(size) && \
     ((size) >= WalSegMinSize && (size) <= WalSegMaxSize))
 
#define XLogSegmentsPerXLogId(wal_segsz_bytes)  \
    (UINT64CONST(0x100000000) / (wal_segsz_bytes))
 
#define XLogSegNoOffsetToRecPtr(segno, offset, wal_segsz_bytes, dest) \
        (dest) = (segno) * (wal_segsz_bytes) + (offset)
 
#define XLogSegmentOffset(xlogptr, wal_segsz_bytes) \
    ((xlogptr) & ((wal_segsz_bytes) - 1))
 
/*
 * Compute a segment number from an XLogRecPtr.
 *
 * For XLByteToSeg, do the computation at face value.  For XLByteToPrevSeg,
 * a boundary byte is taken to be in the previous segment.  This is suitable
 * for deciding which segment to write given a pointer to a record end,
 * for example.
 */
#define XLByteToSeg(xlrp, logSegNo, wal_segsz_bytes) \
    logSegNo = (xlrp) / (wal_segsz_bytes)
 
#define XLByteToPrevSeg(xlrp, logSegNo, wal_segsz_bytes) \
    logSegNo = ((xlrp) - 1) / (wal_segsz_bytes)
 
/*
 * Convert values of GUCs measured in megabytes to equiv. segment count.
 * Rounds down.
 */
#define XLogMBVarToSegs(mbvar, wal_segsz_bytes) \
    ((mbvar) / ((wal_segsz_bytes) / (1024 * 1024)))
 
/*
 * Is an XLogRecPtr within a particular XLOG segment?
 *
 * For XLByteInSeg, do the computation at face value.  For XLByteInPrevSeg,
 * a boundary byte is taken to be in the previous segment.
 */
#define XLByteInSeg(xlrp, logSegNo, wal_segsz_bytes) \
    (((xlrp) / (wal_segsz_bytes)) == (logSegNo))
 
#define XLByteInPrevSeg(xlrp, logSegNo, wal_segsz_bytes) \
    ((((xlrp) - 1) / (wal_segsz_bytes)) == (logSegNo))
 
/* Check if an XLogRecPtr value is in a plausible range */
#define XRecOffIsValid(xlrp) \
        ((xlrp) % XLOG_BLCKSZ >= SizeOfXLogShortPHD)
 
/*
 * The XLog directory and control file (relative to $PGDATA)
 */
#define XLOGDIR             "pg_wal"
#define XLOG_CONTROL_FILE   "global/pg_control"
 
/*
 * These macros encapsulate knowledge about the exact layout of XLog file
 * names, timeline history file names, and archive-status file names.
 */
#define MAXFNAMELEN     64
 
/* Length of XLog file name */
#define XLOG_FNAME_LEN     24
 
/*
 * Generate a WAL segment file name.  Do not use this function in a helper
 * function allocating the result generated.
 */
static inline void
XLogFileName(char *fname, TimeLineID tli, XLogSegNo logSegNo, int wal_segsz_bytes)
{
    snprintf(fname, MAXFNAMELEN, "%08X%08X%08X", tli,
             (uint32) (logSegNo / XLogSegmentsPerXLogId(wal_segsz_bytes)),
             (uint32) (logSegNo % XLogSegmentsPerXLogId(wal_segsz_bytes)));
}
 
static inline void
XLogFileNameById(char *fname, TimeLineID tli, uint32 log, uint32 seg)
{
    snprintf(fname, MAXFNAMELEN, "%08X%08X%08X", tli, log, seg);
}
 
static inline bool
IsXLogFileName(const char *fname)
{
    return (strlen(fname) == XLOG_FNAME_LEN && \
            strspn(fname, "0123456789ABCDEF") == XLOG_FNAME_LEN);
}
 
/*
 * XLOG segment with .partial suffix.  Used by pg_receivewal and at end of
 * archive recovery, when we want to archive a WAL segment but it might not
 * be complete yet.
 */
static inline bool
IsPartialXLogFileName(const char *fname)
{
    return (strlen(fname) == XLOG_FNAME_LEN + strlen(".partial") &&
            strspn(fname, "0123456789ABCDEF") == XLOG_FNAME_LEN &&
            strcmp(fname + XLOG_FNAME_LEN, ".partial") == 0);
}
 
static inline void
XLogFromFileName(const char *fname, TimeLineID *tli, XLogSegNo *logSegNo, int wal_segsz_bytes)
{
    uint32      log;
    uint32      seg;
 
    sscanf(fname, "%08X%08X%08X", tli, &log, &seg);
    *logSegNo = (uint64) log * XLogSegmentsPerXLogId(wal_segsz_bytes) + seg;
}
 
static inline void
XLogFilePath(char *path, TimeLineID tli, XLogSegNo logSegNo, int wal_segsz_bytes)
{
    snprintf(path, MAXPGPATH, XLOGDIR "/%08X%08X%08X", tli,
             (uint32) (logSegNo / XLogSegmentsPerXLogId(wal_segsz_bytes)),
             (uint32) (logSegNo % XLogSegmentsPerXLogId(wal_segsz_bytes)));
}
 
static inline void
TLHistoryFileName(char *fname, TimeLineID tli)
{
    snprintf(fname, MAXFNAMELEN, "%08X.history", tli);
}
 
static inline bool
IsTLHistoryFileName(const char *fname)
{
    return (strlen(fname) == 8 + strlen(".history") &&
            strspn(fname, "0123456789ABCDEF") == 8 &&
            strcmp(fname + 8, ".history") == 0);
}
 
static inline void
TLHistoryFilePath(char *path, TimeLineID tli)
{
    snprintf(path, MAXPGPATH, XLOGDIR "/%08X.history", tli);
}
 
static inline void
StatusFilePath(char *path, const char *xlog, const char *suffix)
{
    snprintf(path, MAXPGPATH, XLOGDIR "/archive_status/%s%s", xlog, suffix);
}
 
static inline void
BackupHistoryFileName(char *fname, TimeLineID tli, XLogSegNo logSegNo, XLogRecPtr startpoint, int wal_segsz_bytes)
{
    snprintf(fname, MAXFNAMELEN, "%08X%08X%08X.%08X.backup", tli,
             (uint32) (logSegNo / XLogSegmentsPerXLogId(wal_segsz_bytes)),
             (uint32) (logSegNo % XLogSegmentsPerXLogId(wal_segsz_bytes)),
             (uint32) (XLogSegmentOffset(startpoint, wal_segsz_bytes)));
}
 
static inline bool
IsBackupHistoryFileName(const char *fname)
{
    return (strlen(fname) > XLOG_FNAME_LEN &&
            strspn(fname, "0123456789ABCDEF") == XLOG_FNAME_LEN &&
            strcmp(fname + strlen(fname) - strlen(".backup"), ".backup") == 0);
}
 
static inline void
BackupHistoryFilePath(char *path, TimeLineID tli, XLogSegNo logSegNo, XLogRecPtr startpoint, int wal_segsz_bytes)
{
    snprintf(path, MAXPGPATH, XLOGDIR "/%08X%08X%08X.%08X.backup", tli,
             (uint32) (logSegNo / XLogSegmentsPerXLogId(wal_segsz_bytes)),
             (uint32) (logSegNo % XLogSegmentsPerXLogId(wal_segsz_bytes)),
             (uint32) (XLogSegmentOffset((startpoint), wal_segsz_bytes)));
}
 
/*
 * Information logged when we detect a change in one of the parameters
 * important for Hot Standby.
 */
typedef struct xl_parameter_change
{
    int         MaxConnections;
    int         max_worker_processes;
    int         max_wal_senders;
    int         max_prepared_xacts;
    int         max_locks_per_xact;
    int         wal_level;
    bool        wal_log_hints;
    bool        track_commit_timestamp;
} xl_parameter_change;
 
/* logs restore point */
typedef struct xl_restore_point
{
    TimestampTz rp_time;
    char        rp_name[MAXFNAMELEN];
} xl_restore_point;
 
/* Overwrite of prior contrecord */
typedef struct xl_overwrite_contrecord
{
    XLogRecPtr  overwritten_lsn;
    TimestampTz overwrite_time;
} xl_overwrite_contrecord;
 
/* End of recovery mark, when we don't do an END_OF_RECOVERY checkpoint */
typedef struct xl_end_of_recovery
{
    TimestampTz end_time;
    TimeLineID  ThisTimeLineID; /* new TLI */
    TimeLineID  PrevTimeLineID; /* previous TLI we forked off from */
    int         wal_level;
} xl_end_of_recovery;
 
/*
 * The functions in xloginsert.c construct a chain of XLogRecData structs
 * to represent the final WAL record.
 */
typedef struct XLogRecData
{
    struct XLogRecData *next;   /* next struct in chain, or NULL */
    const void *data;           /* start of rmgr data to include */
    uint32      len;            /* length of rmgr data to include */
} XLogRecData;
 
struct LogicalDecodingContext;
struct XLogRecordBuffer;
 
/*
 * Method table for resource managers.
 *
 * This struct must be kept in sync with the PG_RMGR definition in
 * rmgr.c.
 *
 * rm_identify must return a name for the record based on xl_info (without
 * reference to the rmid). For example, XLOG_BTREE_VACUUM would be named
 * "VACUUM". rm_desc can then be called to obtain additional detail for the
 * record, if available (e.g. the last block).
 *
 * rm_mask takes as input a page modified by the resource manager and masks
 * out bits that shouldn't be flagged by wal_consistency_checking.
 *
 * RmgrTable[] is indexed by RmgrId values (see rmgrlist.h). If rm_name is
 * NULL, the corresponding RmgrTable entry is considered invalid.
 */
typedef struct RmgrData
{
    const char *rm_name;
    void        (*rm_redo) (XLogReaderState *record);
    void        (*rm_desc) (StringInfo buf, XLogReaderState *record);
    const char *(*rm_identify) (uint8 info);
    void        (*rm_startup) (void);
    void        (*rm_cleanup) (void);
    void        (*rm_mask) (char *pagedata, BlockNumber blkno);
    void        (*rm_decode) (struct LogicalDecodingContext *ctx,
                              struct XLogRecordBuffer *buf);
} RmgrData;
 
extern PGDLLIMPORT RmgrData RmgrTable[];
extern void RmgrStartup(void);
extern void RmgrCleanup(void);
extern void RmgrNotFound(RmgrId rmid);
extern void RegisterCustomRmgr(RmgrId rmid, const RmgrData *rmgr);
 
#ifndef FRONTEND
static inline bool
RmgrIdExists(RmgrId rmid)
{
    return RmgrTable[rmid].rm_name != NULL;
}
 
static inline RmgrData
GetRmgr(RmgrId rmid)
{
    if (unlikely(!RmgrIdExists(rmid)))
        RmgrNotFound(rmid);
    return RmgrTable[rmid];
}
#endif
 
/*
 * Exported to support xlog switching from checkpointer
 */
extern pg_time_t GetLastSegSwitchData(XLogRecPtr *lastSwitchLSN);
extern XLogRecPtr RequestXLogSwitch(bool mark_unimportant);
 
extern void GetOldestRestartPoint(XLogRecPtr *oldrecptr, TimeLineID *oldtli);
 
extern void XLogRecGetBlockRefInfo(XLogReaderState *record, bool pretty,
                                   bool detailed_format, StringInfo buf,
                                   uint32 *fpi_len);
 
/*
 * Exported for the functions in timeline.c and xlogarchive.c.  Only valid
 * in the startup process.
 */
extern PGDLLIMPORT bool ArchiveRecoveryRequested;
extern PGDLLIMPORT bool InArchiveRecovery;
extern PGDLLIMPORT bool StandbyMode;
extern PGDLLIMPORT char *recoveryRestoreCommand;
 
#endif                          /* XLOG_INTERNAL_H */