archive_waldump.c

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/*-------------------------------------------------------------------------
 *
 * archive_waldump.c
 *      A generic facility for reading WAL data from tar archives via archive
 *      streamer.
 *
 * Portions Copyright (c) 2026, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *      src/bin/pg_waldump/archive_waldump.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres_fe.h"
 
#include <unistd.h>
 
#include "access/xlog_internal.h"
#include "common/file_perm.h"
#include "common/hashfn.h"
#include "common/logging.h"
#include "fe_utils/simple_list.h"
#include "pg_waldump.h"
 
/*
 * How many bytes should we try to read from a file at once?
 */
#define READ_CHUNK_SIZE             (128 * 1024)
 
/* Temporary directory for spilled WAL segment files */
char       *TmpWalSegDir = NULL;
 
/*
 * Check if the start segment number is zero; this indicates a request to read
 * any WAL file.
 */
#define READ_ANY_WAL(privateInfo)   ((privateInfo)->start_segno == 0)
 
/*
 * Hash entry representing a WAL segment retrieved from the archive.
 *
 * While WAL segments are typically read sequentially, individual entries
 * maintain their own buffers for the following reasons:
 *
 * 1. Boundary Handling: The archive streamer provides a continuous byte
 * stream. A single streaming chunk may contain the end of one WAL segment
 * and the start of the next. Separate buffers allow us to easily
 * partition and track these bytes by their respective segments.
 *
 * 2. Out-of-Order Support: Dedicated buffers simplify logic when segments
 * are archived or retrieved out of sequence.
 *
 * To minimize the memory footprint, entries and their associated buffers are
 * freed once consumed.  Since pg_waldump does not request the same bytes
 * twice (after it's located the point at which it should start decoding),
 * a segment can be discarded as soon as pg_waldump moves past it.  Moreover,
 * if we read a segment that won't be needed till later, we spill its data to
 * a temporary file instead of retaining it in memory.  This ensures that
 * pg_waldump can process even very large tar archives without needing more
 * than a few WAL segments' worth of memory space.
 */
typedef struct ArchivedWALFile
{
    uint32      status;         /* hash status */
    const char *fname;          /* hash key: WAL segment name */
 
    StringInfo  buf;            /* holds WAL bytes read from archive */
    bool        spilled;        /* true if the WAL data was spilled to a
                                 * temporary file */
 
    int         read_len;       /* total bytes received from archive for this
                                 * segment (same as buf->len, unless we have
                                 * spilled the data to a temp file) */
} ArchivedWALFile;
 
static uint32 hash_string_pointer(const char *s);
#define SH_PREFIX               ArchivedWAL
#define SH_ELEMENT_TYPE         ArchivedWALFile
#define SH_KEY_TYPE             const char *
#define SH_KEY                  fname
#define SH_HASH_KEY(tb, key)    hash_string_pointer(key)
#define SH_EQUAL(tb, a, b)      (strcmp(a, b) == 0)
#define SH_SCOPE                static inline
#define SH_RAW_ALLOCATOR        pg_malloc0
#define SH_DECLARE
#define SH_DEFINE
#include "lib/simplehash.h"
 
typedef struct astreamer_waldump
{
    astreamer   base;
    XLogDumpPrivate *privateInfo;
} astreamer_waldump;
 
static ArchivedWALFile *get_archive_wal_entry(const char *fname,
                                              XLogDumpPrivate *privateInfo);
static bool read_archive_file(XLogDumpPrivate *privateInfo);
static void setup_tmpwal_dir(const char *waldir);
 
static FILE *prepare_tmp_write(const char *fname, XLogDumpPrivate *privateInfo);
static void perform_tmp_write(const char *fname, StringInfo buf, FILE *file);
 
static astreamer *astreamer_waldump_new(XLogDumpPrivate *privateInfo);
static void astreamer_waldump_content(astreamer *streamer,
                                      astreamer_member *member,
                                      const char *data, int len,
                                      astreamer_archive_context context);
static void astreamer_waldump_finalize(astreamer *streamer);
static void astreamer_waldump_free(astreamer *streamer);
 
static bool member_is_wal_file(astreamer_waldump *mystreamer,
                               astreamer_member *member,
                               char **fname);
 
static const astreamer_ops astreamer_waldump_ops = {
    .content = astreamer_waldump_content,
    .finalize = astreamer_waldump_finalize,
    .free = astreamer_waldump_free
};
 
/*
 * Initializes the tar archive reader: opens the archive, builds a hash table
 * for WAL entries, reads ahead until a full WAL page header is available to
 * determine the WAL segment size, and computes start/end segment numbers for
 * filtering.
 */
void
init_archive_reader(XLogDumpPrivate *privateInfo,
                    pg_compress_algorithm compression)
{
    int         fd;
    astreamer  *streamer;
    ArchivedWALFile *entry = NULL;
    XLogLongPageHeader longhdr;
    ArchivedWAL_iterator iter;
 
    /* Open tar archive and store its file descriptor */
    fd = open_file_in_directory(privateInfo->archive_dir,
                                privateInfo->archive_name);
 
    if (fd < 0)
        pg_fatal("could not open file \"%s\"", privateInfo->archive_name);
 
    privateInfo->archive_fd = fd;
    privateInfo->archive_fd_eof = false;
 
    streamer = astreamer_waldump_new(privateInfo);
 
    /* We must first parse the tar archive. */
    streamer = astreamer_tar_parser_new(streamer);
 
    /* If the archive is compressed, decompress before parsing. */
    if (compression == PG_COMPRESSION_GZIP)
        streamer = astreamer_gzip_decompressor_new(streamer);
    else if (compression == PG_COMPRESSION_LZ4)
        streamer = astreamer_lz4_decompressor_new(streamer);
    else if (compression == PG_COMPRESSION_ZSTD)
        streamer = astreamer_zstd_decompressor_new(streamer);
 
    privateInfo->archive_streamer = streamer;
 
    /*
     * Allocate a buffer for reading the archive file to begin content
     * decoding.
     */
    privateInfo->archive_read_buf = pg_malloc(READ_CHUNK_SIZE);
    privateInfo->archive_read_buf_size = READ_CHUNK_SIZE;
 
    /*
     * Hash table storing WAL entries read from the archive with an arbitrary
     * initial size.
     */
    privateInfo->archive_wal_htab = ArchivedWAL_create(8, NULL);
 
    /*
     * Read until we have at least one WAL segment with enough data to extract
     * the WAL segment size from the long page header.
     *
     * We must not rely on cur_file here, because it can become NULL if a
     * member trailer is processed during a read_archive_file() call. Instead,
     * scan the hash table after each read to find any entry with sufficient
     * data.
     */
    while (entry == NULL)
    {
        if (!read_archive_file(privateInfo))
            pg_fatal("could not find WAL in archive \"%s\"",
                     privateInfo->archive_name);
 
        ArchivedWAL_start_iterate(privateInfo->archive_wal_htab, &iter);
        while ((entry = ArchivedWAL_iterate(privateInfo->archive_wal_htab,
                                            &iter)) != NULL)
        {
            if (entry->read_len >= sizeof(XLogLongPageHeaderData))
                break;
        }
    }
 
    /* Extract the WAL segment size from the long page header */
    longhdr = (XLogLongPageHeader) entry->buf->data;
 
    if (!IsValidWalSegSize(longhdr->xlp_seg_size))
    {
        pg_log_error(ngettext("invalid WAL segment size in WAL file from archive \"%s\" (%d byte)",
                              "invalid WAL segment size in WAL file from archive \"%s\" (%d bytes)",
                              longhdr->xlp_seg_size),
                     privateInfo->archive_name, longhdr->xlp_seg_size);
        pg_log_error_detail("The WAL segment size must be a power of two between 1 MB and 1 GB.");
        exit(1);
    }
 
    privateInfo->segsize = longhdr->xlp_seg_size;
 
    /*
     * With the WAL segment size available, we can now initialize the
     * dependent start and end segment numbers.
     */
    Assert(!XLogRecPtrIsInvalid(privateInfo->startptr));
    XLByteToSeg(privateInfo->startptr, privateInfo->start_segno,
                privateInfo->segsize);
 
    if (!XLogRecPtrIsInvalid(privateInfo->endptr))
        XLByteToSeg(privateInfo->endptr, privateInfo->end_segno,
                    privateInfo->segsize);
 
    /*
     * Now that we have initialized the filtering parameters (start_segno and
     * end_segno), we can discard any already-loaded WAL hash table entries
     * for segments we don't actually need.  Subsequent WAL will be filtered
     * automatically by the archive streamer using the updated start_segno and
     * end_segno values.
     */
    ArchivedWAL_start_iterate(privateInfo->archive_wal_htab, &iter);
    while ((entry = ArchivedWAL_iterate(privateInfo->archive_wal_htab,
                                        &iter)) != NULL)
    {
        XLogSegNo   segno;
        TimeLineID  timeline;
 
        XLogFromFileName(entry->fname, &timeline, &segno, privateInfo->segsize);
        if (privateInfo->timeline != timeline ||
            privateInfo->start_segno > segno ||
            privateInfo->end_segno < segno)
            free_archive_wal_entry(entry->fname, privateInfo);
    }
}
 
/*
 * Release the archive streamer chain and close the archive file.
 */
void
free_archive_reader(XLogDumpPrivate *privateInfo)
{
    /*
     * NB: Normally, astreamer_finalize() is called before astreamer_free() to
     * flush any remaining buffered data or to ensure the end of the tar
     * archive is reached.  read_archive_file() may have done so.  However,
     * when decoding WAL we can stop once we hit the end LSN, so we may never
     * have read all of the input file.  In that case any remaining buffered
     * data or unread portion of the archive can be safely ignored.
     */
    astreamer_free(privateInfo->archive_streamer);
 
    /* Free any remaining hash table entries and their buffers. */
    if (privateInfo->archive_wal_htab != NULL)
    {
        ArchivedWAL_iterator iter;
        ArchivedWALFile *entry;
 
        ArchivedWAL_start_iterate(privateInfo->archive_wal_htab, &iter);
        while ((entry = ArchivedWAL_iterate(privateInfo->archive_wal_htab,
                                            &iter)) != NULL)
        {
            if (entry->buf != NULL)
                destroyStringInfo(entry->buf);
        }
        ArchivedWAL_destroy(privateInfo->archive_wal_htab);
        privateInfo->archive_wal_htab = NULL;
    }
 
    /* Free the reusable read buffer. */
    if (privateInfo->archive_read_buf != NULL)
    {
        pg_free(privateInfo->archive_read_buf);
        privateInfo->archive_read_buf = NULL;
    }
 
    /* Close the file. */
    if (close(privateInfo->archive_fd) != 0)
        pg_log_error("could not close file \"%s\": %m",
                     privateInfo->archive_name);
}
 
/*
 * Copies the requested WAL data from the hash entry's buffer into readBuff.
 * If the buffer does not yet contain the needed bytes, fetches more data from
 * the tar archive via the archive streamer.
 */
int
read_archive_wal_page(XLogDumpPrivate *privateInfo, XLogRecPtr targetPagePtr,
                      size_t count, char *readBuff)
{
    char       *p = readBuff;
    size_t      nbytes = count;
    XLogRecPtr  recptr = targetPagePtr;
    int         segsize = privateInfo->segsize;
    XLogSegNo   segno;
    char        fname[MAXFNAMELEN];
    ArchivedWALFile *entry;
 
    /* Identify the segment and locate its entry in the archive hash */
    XLByteToSeg(targetPagePtr, segno, segsize);
    XLogFileName(fname, privateInfo->timeline, segno, segsize);
    entry = get_archive_wal_entry(fname, privateInfo);
    Assert(!entry->spilled);
 
    while (nbytes > 0)
    {
        char       *buf = entry->buf->data;
        int         bufLen = entry->buf->len;
        XLogRecPtr  endPtr;
        XLogRecPtr  startPtr;
 
        /*
         * Calculate the LSN range currently residing in the buffer.
         *
         * read_len tracks total bytes received for this segment, so endPtr is
         * the LSN just past the last buffered byte, and startPtr is the LSN
         * of the first buffered byte.
         */
        XLogSegNoOffsetToRecPtr(segno, entry->read_len, segsize, endPtr);
        startPtr = endPtr - bufLen;
 
        /*
         * Copy the requested WAL record if it exists in the buffer.
         */
        if (bufLen > 0 && startPtr <= recptr && recptr < endPtr)
        {
            int         copyBytes;
            int         offset = recptr - startPtr;
 
            /*
             * Given startPtr <= recptr < endPtr and a total buffer size
             * 'bufLen', the offset (recptr - startPtr) will always be less
             * than 'bufLen'.
             */
            Assert(offset < bufLen);
 
            copyBytes = Min(nbytes, bufLen - offset);
            memcpy(p, buf + offset, copyBytes);
 
            /* Update state for read */
            recptr += copyBytes;
            nbytes -= copyBytes;
            p += copyBytes;
        }
        else
        {
            /*
             * We evidently need to fetch more data.  Raise an error if the
             * archive streamer has moved past our segment (meaning the WAL
             * file in the archive is shorter than expected) or if reading the
             * archive reached EOF.
             */
            if (privateInfo->cur_file != entry)
                pg_fatal("WAL segment \"%s\" in archive \"%s\" is too short: read %zu of %zu bytes",
                         fname, privateInfo->archive_name,
                         (count - nbytes), count);
            if (!read_archive_file(privateInfo))
                pg_fatal("unexpected end of archive \"%s\" while reading \"%s\": read %zu of %zu bytes",
                         privateInfo->archive_name, fname,
                         (count - nbytes), count);
 
            /*
             * Loading more data may have moved hash table entries, so we must
             * re-look-up the one we are reading from.
             */
            entry = ArchivedWAL_lookup(privateInfo->archive_wal_htab, fname);
            /* ... it had better still be there */
            Assert(entry != NULL);
        }
    }
 
    /*
     * Should have successfully read all the requested bytes or reported a
     * failure before this point.
     */
    Assert(nbytes == 0);
 
    /*
     * Return count unchanged; the caller expects this convention, matching
     * the routine that reads WAL pages from physical files.
     */
    return count;
}
 
/*
 * Releases the buffer of a WAL entry that is no longer needed, preventing the
 * accumulation of irrelevant WAL data.  Also removes any associated temporary
 * file and clears privateInfo->cur_file if it points to this entry, so the
 * archive streamer skips subsequent data for it.
 */
void
free_archive_wal_entry(const char *fname, XLogDumpPrivate *privateInfo)
{
    ArchivedWALFile *entry;
    const char *oldfname;
 
    entry = ArchivedWAL_lookup(privateInfo->archive_wal_htab, fname);
 
    if (entry == NULL)
        return;
 
    /* Destroy the buffer */
    destroyStringInfo(entry->buf);
    entry->buf = NULL;
 
    /* Remove temporary file if any */
    if (entry->spilled)
    {
        char        fpath[MAXPGPATH];
 
        snprintf(fpath, MAXPGPATH, "%s/%s", TmpWalSegDir, fname);
 
        if (unlink(fpath) == 0)
            pg_log_debug("removed file \"%s\"", fpath);
    }
 
    /* Clear cur_file if it points to the entry being freed */
    if (privateInfo->cur_file == entry)
        privateInfo->cur_file = NULL;
 
    /*
     * ArchivedWAL_delete_item may cause other hash table entries to move.
     * Therefore, if cur_file isn't NULL now, we have to be prepared to look
     * that entry up again after the deletion.  Fortunately, the entry's fname
     * string won't move.
     */
    oldfname = privateInfo->cur_file ? privateInfo->cur_file->fname : NULL;
 
    ArchivedWAL_delete_item(privateInfo->archive_wal_htab, entry);
 
    if (oldfname)
    {
        privateInfo->cur_file = ArchivedWAL_lookup(privateInfo->archive_wal_htab,
                                                   oldfname);
        /* ... it had better still be there */
        Assert(privateInfo->cur_file != NULL);
    }
}
 
/*
 * Returns the archived WAL entry from the hash table if it already exists.
 * Otherwise, reads more data from the archive until the requested entry is
 * found.  If the archive streamer reads a WAL file from the archive that
 * is not currently needed, that data is spilled to a temporary file for later
 * retrieval.
 *
 * Note that the returned entry might not have been completely read from
 * the archive yet.
 */
static ArchivedWALFile *
get_archive_wal_entry(const char *fname, XLogDumpPrivate *privateInfo)
{
    while (1)
    {
        ArchivedWALFile *entry;
        ArchivedWAL_iterator iter;
 
        /*
         * Search the hash table first.  If the entry is found, return it.
         * Otherwise, the requested WAL entry hasn't been read from the
         * archive yet; we must invoke the archive streamer to fetch it.
         */
        entry = ArchivedWAL_lookup(privateInfo->archive_wal_htab, fname);
 
        if (entry != NULL)
            return entry;
 
        /*
         * Before loading more data, scan the hash table to see if we have
         * loaded any files we don't need yet.  If so, spill their data to
         * disk to conserve memory space.  But don't try to spill a
         * partially-read file; it's not worth the complication.
         */
        ArchivedWAL_start_iterate(privateInfo->archive_wal_htab, &iter);
        while ((entry = ArchivedWAL_iterate(privateInfo->archive_wal_htab,
                                            &iter)) != NULL)
        {
            FILE       *write_fp;
 
            /* OK to spill? */
            if (entry->spilled)
                continue;       /* already spilled */
            if (entry == privateInfo->cur_file)
                continue;       /* still being read */
 
            /* Write out the completed WAL file contents to a temp file. */
            write_fp = prepare_tmp_write(entry->fname, privateInfo);
            perform_tmp_write(entry->fname, entry->buf, write_fp);
            if (fclose(write_fp) != 0)
                pg_fatal("could not close file \"%s/%s\": %m",
                         TmpWalSegDir, entry->fname);
 
            /* resetStringInfo won't release storage, so delete/recreate. */
            destroyStringInfo(entry->buf);
            entry->buf = makeStringInfo();
            entry->spilled = true;
        }
 
        /*
         * Read more data.  If we reach EOF, the desired file is not present.
         */
        if (!read_archive_file(privateInfo))
            pg_fatal("could not find WAL \"%s\" in archive \"%s\"",
                     fname, privateInfo->archive_name);
    }
}
 
/*
 * Reads a chunk from the archive file and passes it through the streamer
 * pipeline for decompression (if needed) and tar member extraction.
 *
 * Returns true if successful, false if there is no more data.
 *
 * Callers must be aware that a single call may trigger multiple callbacks
 * in astreamer_waldump_content, so privateInfo->cur_file can change value
 * (or become NULL) during a call.  In particular, cur_file is set to NULL
 * when the ASTREAMER_MEMBER_TRAILER callback fires at the end of a tar
 * member; it is then set to a new entry when the next WAL member's
 * ASTREAMER_MEMBER_HEADER callback fires, which may or may not happen
 * within the same call.
 */
static bool
read_archive_file(XLogDumpPrivate *privateInfo)
{
    int         rc;
 
    /* Fail if we already reached EOF in a prior call. */
    if (privateInfo->archive_fd_eof)
        return false;
 
    /* Try to read some more data. */
    rc = read(privateInfo->archive_fd, privateInfo->archive_read_buf,
              privateInfo->archive_read_buf_size);
    if (rc < 0)
        pg_fatal("could not read file \"%s\": %m",
                 privateInfo->archive_name);
 
    /*
     * Decompress (if required), and then parse the previously read contents
     * of the tar file.
     */
    if (rc > 0)
        astreamer_content(privateInfo->archive_streamer, NULL,
                          privateInfo->archive_read_buf, rc,
                          ASTREAMER_UNKNOWN);
    else
    {
        /*
         * We reached EOF, but there is probably still data queued in the
         * astreamer pipeline's buffers.  Flush it out to ensure that we
         * process everything.
         */
        astreamer_finalize(privateInfo->archive_streamer);
        /* Set flag to ensure we don't finalize more than once. */
        privateInfo->archive_fd_eof = true;
    }
 
    return true;
}
 
/*
 * Set up a temporary directory to temporarily store WAL segments.
 */
static void
setup_tmpwal_dir(const char *waldir)
{
    const char *tmpdir = getenv("TMPDIR");
    char       *template;
 
    Assert(TmpWalSegDir == NULL);
 
    /*
     * Use the directory specified by the TMPDIR environment variable. If it's
     * not set, fall back to the provided WAL directory to store WAL files
     * temporarily.
     */
    template = psprintf("%s/waldump_tmp-XXXXXX",
                        tmpdir ? tmpdir : waldir);
    TmpWalSegDir = mkdtemp(template);
 
    if (TmpWalSegDir == NULL)
        pg_fatal("could not create directory \"%s\": %m", template);
 
    canonicalize_path(TmpWalSegDir);
 
    pg_log_debug("created directory \"%s\"", TmpWalSegDir);
}
 
/*
 * Open a file in the temporary spill directory for writing an out-of-order
 * WAL segment, creating the directory if not already done.
 * Returns the open file handle.
 */
static FILE *
prepare_tmp_write(const char *fname, XLogDumpPrivate *privateInfo)
{
    char        fpath[MAXPGPATH];
    FILE       *file;
 
    /* Setup temporary directory to store WAL segments, if we didn't already */
    if (unlikely(TmpWalSegDir == NULL))
        setup_tmpwal_dir(privateInfo->archive_dir);
 
    snprintf(fpath, MAXPGPATH, "%s/%s", TmpWalSegDir, fname);
 
    /* Open the spill file for writing */
    file = fopen(fpath, PG_BINARY_W);
    if (file == NULL)
        pg_fatal("could not create file \"%s\": %m", fpath);
 
#ifndef WIN32
    if (chmod(fpath, pg_file_create_mode))
        pg_fatal("could not set permissions on file \"%s\": %m",
                 fpath);
#endif
 
    pg_log_debug("spilling to temporary file \"%s\"", fpath);
 
    return file;
}
 
/*
 * Write buffer data to the given file handle.
 */
static void
perform_tmp_write(const char *fname, StringInfo buf, FILE *file)
{
    Assert(file);
 
    errno = 0;
    if (buf->len > 0 && fwrite(buf->data, buf->len, 1, file) != 1)
    {
        /*
         * If write didn't set errno, assume problem is no disk space
         */
        if (errno == 0)
            errno = ENOSPC;
        pg_fatal("could not write to file \"%s/%s\": %m", TmpWalSegDir, fname);
    }
}
 
/*
 * Create an astreamer that can read WAL from tar file.
 */
static astreamer *
astreamer_waldump_new(XLogDumpPrivate *privateInfo)
{
    astreamer_waldump *streamer;
 
    streamer = palloc0_object(astreamer_waldump);
    *((const astreamer_ops **) &streamer->base.bbs_ops) =
        &astreamer_waldump_ops;
 
    streamer->privateInfo = privateInfo;
 
    return &streamer->base;
}
 
/*
 * Main entry point of the archive streamer for reading WAL data from a tar
 * file. If a member is identified as a valid WAL file, a hash entry is created
 * for it, and its contents are copied into that entry's buffer, making them
 * accessible to the decoding routine.
 */
static void
astreamer_waldump_content(astreamer *streamer, astreamer_member *member,
                          const char *data, int len,
                          astreamer_archive_context context)
{
    astreamer_waldump *mystreamer = (astreamer_waldump *) streamer;
    XLogDumpPrivate *privateInfo = mystreamer->privateInfo;
 
    Assert(context != ASTREAMER_UNKNOWN);
 
    switch (context)
    {
        case ASTREAMER_MEMBER_HEADER:
            {
                char       *fname = NULL;
                ArchivedWALFile *entry;
                bool        found;
 
                /* Shouldn't see MEMBER_HEADER in the middle of a file */
                Assert(privateInfo->cur_file == NULL);
 
                pg_log_debug("reading \"%s\"", member->pathname);
 
                if (!member_is_wal_file(mystreamer, member, &fname))
                    break;
 
                /*
                 * Skip range filtering during initial startup, before the WAL
                 * segment size and segment number bounds are known.
                 */
                if (!READ_ANY_WAL(privateInfo))
                {
                    XLogSegNo   segno;
                    TimeLineID  timeline;
 
                    /*
                     * Skip the segment if the timeline does not match, if it
                     * falls outside the caller-specified range.
                     */
                    XLogFromFileName(fname, &timeline, &segno, privateInfo->segsize);
                    if (privateInfo->timeline != timeline ||
                        privateInfo->start_segno > segno ||
                        privateInfo->end_segno < segno)
                    {
                        pfree(fname);
                        break;
                    }
                }
 
                /*
                 * Note: ArchivedWAL_insert may cause existing hash table
                 * entries to move.  While cur_file is known to be NULL right
                 * now, read_archive_wal_page may have a live hash entry
                 * pointer, which it needs to take care to update after
                 * read_archive_file completes.
                 */
                entry = ArchivedWAL_insert(privateInfo->archive_wal_htab,
                                           fname, &found);
 
                /*
                 * Shouldn't happen, but if it does, simply ignore the
                 * duplicate WAL file.
                 */
                if (found)
                {
                    pg_log_warning("ignoring duplicate WAL \"%s\" found in archive \"%s\"",
                                   member->pathname, privateInfo->archive_name);
                    pfree(fname);
                    break;
                }
 
                entry->buf = makeStringInfo();
                entry->spilled = false;
                entry->read_len = 0;
                privateInfo->cur_file = entry;
            }
            break;
 
        case ASTREAMER_MEMBER_CONTENTS:
            if (privateInfo->cur_file)
            {
                appendBinaryStringInfo(privateInfo->cur_file->buf, data, len);
                privateInfo->cur_file->read_len += len;
            }
            break;
 
        case ASTREAMER_MEMBER_TRAILER:
 
            /*
             * End of this tar member; mark cur_file NULL so subsequent
             * content callbacks (if any) know no WAL file is currently
             * active.
             */
            privateInfo->cur_file = NULL;
            break;
 
        case ASTREAMER_ARCHIVE_TRAILER:
            break;
 
        default:
            /* Shouldn't happen. */
            pg_fatal("unexpected state while parsing tar file");
    }
}
 
/*
 * End-of-stream processing for an astreamer_waldump stream.  This is a
 * terminal streamer so it must have no successor.
 */
static void
astreamer_waldump_finalize(astreamer *streamer)
{
    Assert(streamer->bbs_next == NULL);
}
 
/*
 * Free memory associated with an astreamer_waldump stream.
 */
static void
astreamer_waldump_free(astreamer *streamer)
{
    Assert(streamer->bbs_next == NULL);
    pfree(streamer);
}
 
/*
 * Returns true if the archive member name matches the WAL naming format. If
 * successful, it also outputs the WAL segment name.
 */
static bool
member_is_wal_file(astreamer_waldump *mystreamer, astreamer_member *member,
                   char **fname)
{
    int         pathlen;
    char        pathname[MAXPGPATH];
    char       *filename;
 
    /* We are only interested in normal files */
    if (!member->is_regular)
        return false;
 
    if (strlen(member->pathname) < XLOG_FNAME_LEN)
        return false;
 
    /*
     * For a correct comparison, we must remove any '.' or '..' components
     * from the member pathname. Similar to member_verify_header(), we prepend
     * './' to the path so that canonicalize_path() can properly resolve and
     * strip these references from the tar member name.
     */
    snprintf(pathname, MAXPGPATH, "./%s", member->pathname);
    canonicalize_path(pathname);
    pathlen = strlen(pathname);
 
    /* Skip files in subdirectories other than pg_wal/ */
    if (pathlen > XLOG_FNAME_LEN &&
        strncmp(pathname, XLOGDIR, strlen(XLOGDIR)) != 0)
        return false;
 
    /* WAL file may appear with a full path (e.g., pg_wal/<name>) */
    filename = pathname + (pathlen - XLOG_FNAME_LEN);
    if (!IsXLogFileName(filename))
        return false;
 
    *fname = pnstrdup(filename, XLOG_FNAME_LEN);
 
    return true;
}
 
/*
 * Helper function for WAL file hash table.
 */
static uint32
hash_string_pointer(const char *s)
{
    const unsigned char *ss = (const unsigned char *) s;
 
    return hash_bytes(ss, strlen(s));
}