walsummary.c

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/*-------------------------------------------------------------------------
 *
 * walsummary.c
 *    Functions for accessing and managing WAL summary data.
 *
 * Portions Copyright (c) 2010-2025, PostgreSQL Global Development Group
 *
 * src/backend/backup/walsummary.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include <sys/stat.h>
#include <unistd.h>
 
#include "access/xlog_internal.h"
#include "backup/walsummary.h"
#include "common/int.h"
#include "utils/wait_event.h"
 
static bool IsWalSummaryFilename(char *filename);
static int  ListComparatorForWalSummaryFiles(const ListCell *a,
                                             const ListCell *b);
 
/*
 * Get a list of WAL summaries.
 *
 * If tli != 0, only WAL summaries with the indicated TLI will be included.
 *
 * If start_lsn != InvalidXLogRecPtr, only summaries that end after the
 * indicated LSN will be included.
 *
 * If end_lsn != InvalidXLogRecPtr, only summaries that start before the
 * indicated LSN will be included.
 *
 * The intent is that you can call GetWalSummaries(tli, start_lsn, end_lsn)
 * to get all WAL summaries on the indicated timeline that overlap the
 * specified LSN range.
 */
List *
GetWalSummaries(TimeLineID tli, XLogRecPtr start_lsn, XLogRecPtr end_lsn)
{
    DIR        *sdir;
    struct dirent *dent;
    List       *result = NIL;
 
    sdir = AllocateDir(XLOGDIR "/summaries");
    while ((dent = ReadDir(sdir, XLOGDIR "/summaries")) != NULL)
    {
        WalSummaryFile *ws;
        uint32      tmp[5];
        TimeLineID  file_tli;
        XLogRecPtr  file_start_lsn;
        XLogRecPtr  file_end_lsn;
 
        /* Decode filename, or skip if it's not in the expected format. */
        if (!IsWalSummaryFilename(dent->d_name))
            continue;
        sscanf(dent->d_name, "%08X%08X%08X%08X%08X",
               &tmp[0], &tmp[1], &tmp[2], &tmp[3], &tmp[4]);
        file_tli = tmp[0];
        file_start_lsn = ((uint64) tmp[1]) << 32 | tmp[2];
        file_end_lsn = ((uint64) tmp[3]) << 32 | tmp[4];
 
        /* Skip if it doesn't match the filter criteria. */
        if (tli != 0 && tli != file_tli)
            continue;
        if (!XLogRecPtrIsInvalid(start_lsn) && start_lsn >= file_end_lsn)
            continue;
        if (!XLogRecPtrIsInvalid(end_lsn) && end_lsn <= file_start_lsn)
            continue;
 
        /* Add it to the list. */
        ws = palloc(sizeof(WalSummaryFile));
        ws->tli = file_tli;
        ws->start_lsn = file_start_lsn;
        ws->end_lsn = file_end_lsn;
        result = lappend(result, ws);
    }
    FreeDir(sdir);
 
    return result;
}
 
/*
 * Build a new list of WAL summaries based on an existing list, but filtering
 * out summaries that don't match the search parameters.
 *
 * If tli != 0, only WAL summaries with the indicated TLI will be included.
 *
 * If start_lsn != InvalidXLogRecPtr, only summaries that end after the
 * indicated LSN will be included.
 *
 * If end_lsn != InvalidXLogRecPtr, only summaries that start before the
 * indicated LSN will be included.
 */
List *
FilterWalSummaries(List *wslist, TimeLineID tli,
                   XLogRecPtr start_lsn, XLogRecPtr end_lsn)
{
    List       *result = NIL;
    ListCell   *lc;
 
    /* Loop over input. */
    foreach(lc, wslist)
    {
        WalSummaryFile *ws = lfirst(lc);
 
        /* Skip if it doesn't match the filter criteria. */
        if (tli != 0 && tli != ws->tli)
            continue;
        if (!XLogRecPtrIsInvalid(start_lsn) && start_lsn > ws->end_lsn)
            continue;
        if (!XLogRecPtrIsInvalid(end_lsn) && end_lsn < ws->start_lsn)
            continue;
 
        /* Add it to the result list. */
        result = lappend(result, ws);
    }
 
    return result;
}
 
/*
 * Check whether the supplied list of WalSummaryFile objects covers the
 * whole range of LSNs from start_lsn to end_lsn. This function ignores
 * timelines, so the caller should probably filter using the appropriate
 * timeline before calling this.
 *
 * If the whole range of LSNs is covered, returns true, otherwise false.
 * If false is returned, *missing_lsn is set either to InvalidXLogRecPtr
 * if there are no WAL summary files in the input list, or to the first LSN
 * in the range that is not covered by a WAL summary file in the input list.
 */
bool
WalSummariesAreComplete(List *wslist, XLogRecPtr start_lsn,
                        XLogRecPtr end_lsn, XLogRecPtr *missing_lsn)
{
    XLogRecPtr  current_lsn = start_lsn;
    ListCell   *lc;
 
    /* Special case for empty list. */
    if (wslist == NIL)
    {
        *missing_lsn = InvalidXLogRecPtr;
        return false;
    }
 
    /* Make a private copy of the list and sort it by start LSN. */
    wslist = list_copy(wslist);
    list_sort(wslist, ListComparatorForWalSummaryFiles);
 
    /*
     * Consider summary files in order of increasing start_lsn, advancing the
     * known-summarized range from start_lsn toward end_lsn.
     *
     * Normally, the summary files should cover non-overlapping WAL ranges,
     * but this algorithm is intended to be correct even in case of overlap.
     */
    foreach(lc, wslist)
    {
        WalSummaryFile *ws = lfirst(lc);
 
        if (ws->start_lsn > current_lsn)
        {
            /* We found a gap. */
            break;
        }
        if (ws->end_lsn > current_lsn)
        {
            /*
             * Next summary extends beyond end of previous summary, so extend
             * the end of the range known to be summarized.
             */
            current_lsn = ws->end_lsn;
 
            /*
             * If the range we know to be summarized has reached the required
             * end LSN, we have proved completeness.
             */
            if (current_lsn >= end_lsn)
                return true;
        }
    }
 
    /*
     * We either ran out of summary files without reaching the end LSN, or we
     * hit a gap in the sequence that resulted in us bailing out of the loop
     * above.
     */
    *missing_lsn = current_lsn;
    return false;
}
 
/*
 * Open a WAL summary file.
 *
 * This will throw an error in case of trouble. As an exception, if
 * missing_ok = true and the trouble is specifically that the file does
 * not exist, it will not throw an error and will return a value less than 0.
 */
File
OpenWalSummaryFile(WalSummaryFile *ws, bool missing_ok)
{
    char        path[MAXPGPATH];
    File        file;
 
    snprintf(path, MAXPGPATH,
             XLOGDIR "/summaries/%08X%08X%08X%08X%08X.summary",
             ws->tli,
             LSN_FORMAT_ARGS(ws->start_lsn),
             LSN_FORMAT_ARGS(ws->end_lsn));
 
    file = PathNameOpenFile(path, O_RDONLY);
    if (file < 0 && (errno != EEXIST || !missing_ok))
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not open file \"%s\": %m", path)));
 
    return file;
}
 
/*
 * Remove a WAL summary file if the last modification time precedes the
 * cutoff time.
 */
void
RemoveWalSummaryIfOlderThan(WalSummaryFile *ws, time_t cutoff_time)
{
    char        path[MAXPGPATH];
    struct stat statbuf;
 
    snprintf(path, MAXPGPATH,
             XLOGDIR "/summaries/%08X%08X%08X%08X%08X.summary",
             ws->tli,
             LSN_FORMAT_ARGS(ws->start_lsn),
             LSN_FORMAT_ARGS(ws->end_lsn));
 
    if (lstat(path, &statbuf) != 0)
    {
        if (errno == ENOENT)
            return;
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not stat file \"%s\": %m", path)));
    }
    if (statbuf.st_mtime >= cutoff_time)
        return;
    if (unlink(path) != 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not stat file \"%s\": %m", path)));
    ereport(DEBUG2,
            (errmsg_internal("removing file \"%s\"", path)));
}
 
/*
 * Test whether a filename looks like a WAL summary file.
 */
static bool
IsWalSummaryFilename(char *filename)
{
    return strspn(filename, "0123456789ABCDEF") == 40 &&
        strcmp(filename + 40, ".summary") == 0;
}
 
/*
 * Data read callback for use with CreateBlockRefTableReader.
 */
int
ReadWalSummary(void *wal_summary_io, void *data, int length)
{
    WalSummaryIO *io = wal_summary_io;
    int         nbytes;
 
    nbytes = FileRead(io->file, data, length, io->filepos,
                      WAIT_EVENT_WAL_SUMMARY_READ);
    if (nbytes < 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not read file \"%s\": %m",
                        FilePathName(io->file))));
 
    io->filepos += nbytes;
    return nbytes;
}
 
/*
 * Data write callback for use with WriteBlockRefTable.
 */
int
WriteWalSummary(void *wal_summary_io, void *data, int length)
{
    WalSummaryIO *io = wal_summary_io;
    int         nbytes;
 
    nbytes = FileWrite(io->file, data, length, io->filepos,
                       WAIT_EVENT_WAL_SUMMARY_WRITE);
    if (nbytes < 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not write file \"%s\": %m",
                        FilePathName(io->file))));
    if (nbytes != length)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not write file \"%s\": wrote only %d of %d bytes at offset %u",
                        FilePathName(io->file), nbytes,
                        length, (unsigned) io->filepos),
                 errhint("Check free disk space.")));
 
    io->filepos += nbytes;
    return nbytes;
}
 
/*
 * Error-reporting callback for use with CreateBlockRefTableReader.
 */
void
ReportWalSummaryError(void *callback_arg, char *fmt,...)
{
    StringInfoData buf;
    va_list     ap;
    int         needed;
 
    initStringInfo(&buf);
    for (;;)
    {
        va_start(ap, fmt);
        needed = appendStringInfoVA(&buf, fmt, ap);
        va_end(ap);
        if (needed == 0)
            break;
        enlargeStringInfo(&buf, needed);
    }
    ereport(ERROR,
            errcode(ERRCODE_DATA_CORRUPTED),
            errmsg_internal("%s", buf.data));
}
 
/*
 * Comparator to sort a List of WalSummaryFile objects by start_lsn.
 */
static int
ListComparatorForWalSummaryFiles(const ListCell *a, const ListCell *b)
{
    WalSummaryFile *ws1 = lfirst(a);
    WalSummaryFile *ws2 = lfirst(b);
 
    return pg_cmp_u64(ws1->start_lsn, ws2->start_lsn);
}