pg_resetwal.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * pg_resetwal.c
 *    A utility to "zero out" the xlog when it's corrupt beyond recovery.
 *    Can also rebuild pg_control if needed.
 *
 * The theory of operation is fairly simple:
 *    1. Read the existing pg_control (which will include the last
 *       checkpoint record).  If it is an old format then update to
 *       current format.
 *    2. If pg_control is corrupt, attempt to intuit reasonable values,
 *       by scanning the old xlog if necessary.
 *    3. Modify pg_control to reflect a "shutdown" state with a checkpoint
 *       record at the start of xlog.
 *    4. Flush the existing xlog files and write a new segment with
 *       just a checkpoint record in it.  The new segment is positioned
 *       just past the end of the old xlog, so that existing LSNs in
 *       data pages will appear to be "in the past".
 * This is all pretty straightforward except for the intuition part of
 * step 2 ...
 *
 *
 * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/bin/pg_resetwal/pg_resetwal.c
 *
 *-------------------------------------------------------------------------
 */

/*
 * We have to use postgres.h not postgres_fe.h here, because there's so much
 * backend-only stuff in the XLOG include files we need.  But we need a
 * frontend-ish environment otherwise.  Hence this ugly hack.
 */
#define FRONTEND 1

#include "postgres.h"

#include <dirent.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>

#include "access/transam.h"
#include "access/tuptoaster.h"
#include "access/multixact.h"
#include "access/xlog.h"
#include "access/xlog_internal.h"
#include "catalog/catversion.h"
#include "catalog/pg_control.h"
#include "common/fe_memutils.h"
#include "common/file_perm.h"
#include "common/restricted_token.h"
#include "storage/large_object.h"
#include "pg_getopt.h"
#include "getopt_long.h"


static ControlFileData ControlFile; /* pg_control values */
static XLogSegNo newXlogSegNo;  /* new XLOG segment # */
static bool guessed = false;    /* T if we had to guess at any values */
static const char *progname;
static uint32 set_xid_epoch = (uint32) -1;
static TransactionId set_xid = 0;
static TransactionId set_oldest_commit_ts_xid = 0;
static TransactionId set_newest_commit_ts_xid = 0;
static Oid  set_oid = 0;
static MultiXactId set_mxid = 0;
static MultiXactOffset set_mxoff = (MultiXactOffset) -1;
static uint32 minXlogTli = 0;
static XLogSegNo minXlogSegNo = 0;
static int  WalSegSz;
static int  set_wal_segsize;

static void CheckDataVersion(void);
static bool ReadControlFile(void);
static void GuessControlValues(void);
static void PrintControlValues(bool guessed);
static void PrintNewControlValues(void);
static void RewriteControlFile(void);
static void FindEndOfXLOG(void);
static void KillExistingXLOG(void);
static void KillExistingArchiveStatus(void);
static void WriteEmptyXLOG(void);
static void usage(void);


int
main(int argc, char *argv[])
{
    static struct option long_options[] = {
        {"commit-timestamp-ids", required_argument, NULL, 'c'},
        {"pgdata", required_argument, NULL, 'D'},
        {"epoch", required_argument, NULL, 'e'},
        {"force", no_argument, NULL, 'f'},
        {"next-wal-file", required_argument, NULL, 'l'},
        {"multixact-ids", required_argument, NULL, 'm'},
        {"dry-run", no_argument, NULL, 'n'},
        {"next-oid", required_argument, NULL, 'o'},
        {"multixact-offset", required_argument, NULL, 'O'},
        {"next-transaction-id", required_argument, NULL, 'x'},
        {"wal-segsize", required_argument, NULL, 1},
        {NULL, 0, NULL, 0}
    };

    int         c;
    bool        force = false;
    bool        noupdate = false;
    MultiXactId set_oldestmxid = 0;
    char       *endptr;
    char       *endptr2;
    char       *DataDir = NULL;
    char       *log_fname = NULL;
    int         fd;

    set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_resetwal"));

    progname = get_progname(argv[0]);

    if (argc > 1)
    {
        if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-?") == 0)
        {
            usage();
            exit(0);
        }
        if (strcmp(argv[1], "--version") == 0 || strcmp(argv[1], "-V") == 0)
        {
            puts("pg_resetwal (PostgreSQL) " PG_VERSION);
            exit(0);
        }
    }


    while ((c = getopt_long(argc, argv, "c:D:e:fl:m:no:O:x:", long_options, NULL)) != -1)
    {
        switch (c)
        {
            case 'D':
                DataDir = optarg;
                break;

            case 'f':
                force = true;
                break;

            case 'n':
                noupdate = true;
                break;

            case 'e':
                set_xid_epoch = strtoul(optarg, &endptr, 0);
                if (endptr == optarg || *endptr != '\0')
                {
                    /*------
                      translator: the second %s is a command line argument (-e, etc) */
                    fprintf(stderr, _("%s: invalid argument for option %s\n"), progname, "-e");
                    fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
                    exit(1);
                }
                if (set_xid_epoch == -1)
                {
                    fprintf(stderr, _("%s: transaction ID epoch (-e) must not be -1\n"), progname);
                    exit(1);
                }
                break;

            case 'x':
                set_xid = strtoul(optarg, &endptr, 0);
                if (endptr == optarg || *endptr != '\0')
                {
                    fprintf(stderr, _("%s: invalid argument for option %s\n"), progname, "-x");
                    fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
                    exit(1);
                }
                if (set_xid == 0)
                {
                    fprintf(stderr, _("%s: transaction ID (-x) must not be 0\n"), progname);
                    exit(1);
                }
                break;

            case 'c':
                set_oldest_commit_ts_xid = strtoul(optarg, &endptr, 0);
                if (endptr == optarg || *endptr != ',')
                {
                    fprintf(stderr, _("%s: invalid argument for option %s\n"), progname, "-c");
                    fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
                    exit(1);
                }
                set_newest_commit_ts_xid = strtoul(endptr + 1, &endptr2, 0);
                if (endptr2 == endptr + 1 || *endptr2 != '\0')
                {
                    fprintf(stderr, _("%s: invalid argument for option %s\n"), progname, "-c");
                    fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
                    exit(1);
                }

                if (set_oldest_commit_ts_xid < 2 &&
                    set_oldest_commit_ts_xid != 0)
                {
                    fprintf(stderr, _("%s: transaction ID (-c) must be either 0 or greater than or equal to 2\n"), progname);
                    exit(1);
                }

                if (set_newest_commit_ts_xid < 2 &&
                    set_newest_commit_ts_xid != 0)
                {
                    fprintf(stderr, _("%s: transaction ID (-c) must be either 0 or greater than or equal to 2\n"), progname);
                    exit(1);
                }
                break;

            case 'o':
                set_oid = strtoul(optarg, &endptr, 0);
                if (endptr == optarg || *endptr != '\0')
                {
                    fprintf(stderr, _("%s: invalid argument for option %s\n"), progname, "-o");
                    fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
                    exit(1);
                }
                if (set_oid == 0)
                {
                    fprintf(stderr, _("%s: OID (-o) must not be 0\n"), progname);
                    exit(1);
                }
                break;

            case 'm':
                set_mxid = strtoul(optarg, &endptr, 0);
                if (endptr == optarg || *endptr != ',')
                {
                    fprintf(stderr, _("%s: invalid argument for option %s\n"), progname, "-m");
                    fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
                    exit(1);
                }

                set_oldestmxid = strtoul(endptr + 1, &endptr2, 0);
                if (endptr2 == endptr + 1 || *endptr2 != '\0')
                {
                    fprintf(stderr, _("%s: invalid argument for option %s\n"), progname, "-m");
                    fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
                    exit(1);
                }
                if (set_mxid == 0)
                {
                    fprintf(stderr, _("%s: multitransaction ID (-m) must not be 0\n"), progname);
                    exit(1);
                }

                /*
                 * XXX It'd be nice to have more sanity checks here, e.g. so
                 * that oldest is not wrapped around w.r.t. nextMulti.
                 */
                if (set_oldestmxid == 0)
                {
                    fprintf(stderr, _("%s: oldest multitransaction ID (-m) must not be 0\n"),
                            progname);
                    exit(1);
                }
                break;

            case 'O':
                set_mxoff = strtoul(optarg, &endptr, 0);
                if (endptr == optarg || *endptr != '\0')
                {
                    fprintf(stderr, _("%s: invalid argument for option %s\n"), progname, "-O");
                    fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
                    exit(1);
                }
                if (set_mxoff == -1)
                {
                    fprintf(stderr, _("%s: multitransaction offset (-O) must not be -1\n"), progname);
                    exit(1);
                }
                break;

            case 'l':
                if (strspn(optarg, "01234567890ABCDEFabcdef") != XLOG_FNAME_LEN)
                {
                    fprintf(stderr, _("%s: invalid argument for option %s\n"), progname, "-l");
                    fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
                    exit(1);
                }

                /*
                 * XLogFromFileName requires wal segment size which is not yet
                 * set. Hence wal details are set later on.
                 */
                log_fname = pg_strdup(optarg);
                break;

            case 1:
                set_wal_segsize = strtol(optarg, &endptr, 10) * 1024 * 1024;
                if (endptr == optarg || *endptr != '\0')
                {
                    fprintf(stderr,
                            _("%s: argument of --wal-segsize must be a number\n"),
                            progname);
                    exit(1);
                }
                if (!IsValidWalSegSize(set_wal_segsize))
                {
                    fprintf(stderr,
                            _("%s: argument of --wal-segsize must be a power of 2 between 1 and 1024\n"),
                            progname);
                    exit(1);
                }
                break;

            default:
                fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
                exit(1);
        }
    }

    if (DataDir == NULL && optind < argc)
        DataDir = argv[optind++];

    /* Complain if any arguments remain */
    if (optind < argc)
    {
        fprintf(stderr, _("%s: too many command-line arguments (first is \"%s\")\n"),
                progname, argv[optind]);
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    if (DataDir == NULL)
    {
        fprintf(stderr, _("%s: no data directory specified\n"), progname);
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
        exit(1);
    }

    /*
     * Don't allow pg_resetwal to be run as root, to avoid overwriting the
     * ownership of files in the data directory. We need only check for root
     * -- any other user won't have sufficient permissions to modify files in
     * the data directory.
     */
#ifndef WIN32
    if (geteuid() == 0)
    {
        fprintf(stderr, _("%s: cannot be executed by \"root\"\n"),
                progname);
        fprintf(stderr, _("You must run %s as the PostgreSQL superuser.\n"),
                progname);
        exit(1);
    }
#endif

    get_restricted_token(progname);

    /* Set mask based on PGDATA permissions */
    if (!GetDataDirectoryCreatePerm(DataDir))
    {
        fprintf(stderr, _("%s: could not read permissions of directory \"%s\": %s\n"),
                progname, DataDir, strerror(errno));
        exit(1);
    }

    umask(pg_mode_mask);

    if (chdir(DataDir) < 0)
    {
        fprintf(stderr, _("%s: could not change directory to \"%s\": %s\n"),
                progname, DataDir, strerror(errno));
        exit(1);
    }

    /* Check that data directory matches our server version */
    CheckDataVersion();

    /*
     * Check for a postmaster lock file --- if there is one, refuse to
     * proceed, on grounds we might be interfering with a live installation.
     */
    if ((fd = open("postmaster.pid", O_RDONLY, 0)) < 0)
    {
        if (errno != ENOENT)
        {
            fprintf(stderr, _("%s: could not open file \"%s\" for reading: %s\n"),
                    progname, "postmaster.pid", strerror(errno));
            exit(1);
        }
    }
    else
    {
        fprintf(stderr, _("%s: lock file \"%s\" exists\n"
                          "Is a server running?  If not, delete the lock file and try again.\n"),
                progname, "postmaster.pid");
        exit(1);
    }

    /*
     * Attempt to read the existing pg_control file
     */
    if (!ReadControlFile())
        GuessControlValues();

    /*
     * If no new WAL segment size was specified, use the control file value.
     */
    if (set_wal_segsize != 0)
        WalSegSz = set_wal_segsize;
    else
        WalSegSz = ControlFile.xlog_seg_size;

    if (log_fname != NULL)
        XLogFromFileName(log_fname, &minXlogTli, &minXlogSegNo, WalSegSz);

    /*
     * Also look at existing segment files to set up newXlogSegNo
     */
    FindEndOfXLOG();

    /*
     * If we're not going to proceed with the reset, print the current control
     * file parameters.
     */
    if ((guessed && !force) || noupdate)
        PrintControlValues(guessed);

    /*
     * Adjust fields if required by switches.  (Do this now so that printout,
     * if any, includes these values.)
     */
    if (set_xid_epoch != -1)
        ControlFile.checkPointCopy.nextXidEpoch = set_xid_epoch;

    if (set_xid != 0)
    {
        ControlFile.checkPointCopy.nextXid = set_xid;

        /*
         * For the moment, just set oldestXid to a value that will force
         * immediate autovacuum-for-wraparound.  It's not clear whether adding
         * user control of this is useful, so let's just do something that's
         * reasonably safe.  The magic constant here corresponds to the
         * maximum allowed value of autovacuum_freeze_max_age.
         */
        ControlFile.checkPointCopy.oldestXid = set_xid - 2000000000;
        if (ControlFile.checkPointCopy.oldestXid < FirstNormalTransactionId)
            ControlFile.checkPointCopy.oldestXid += FirstNormalTransactionId;
        ControlFile.checkPointCopy.oldestXidDB = InvalidOid;
    }

    if (set_oldest_commit_ts_xid != 0)
        ControlFile.checkPointCopy.oldestCommitTsXid = set_oldest_commit_ts_xid;
    if (set_newest_commit_ts_xid != 0)
        ControlFile.checkPointCopy.newestCommitTsXid = set_newest_commit_ts_xid;

    if (set_oid != 0)
        ControlFile.checkPointCopy.nextOid = set_oid;

    if (set_mxid != 0)
    {
        ControlFile.checkPointCopy.nextMulti = set_mxid;

        ControlFile.checkPointCopy.oldestMulti = set_oldestmxid;
        if (ControlFile.checkPointCopy.oldestMulti < FirstMultiXactId)
            ControlFile.checkPointCopy.oldestMulti += FirstMultiXactId;
        ControlFile.checkPointCopy.oldestMultiDB = InvalidOid;
    }

    if (set_mxoff != -1)
        ControlFile.checkPointCopy.nextMultiOffset = set_mxoff;

    if (minXlogTli > ControlFile.checkPointCopy.ThisTimeLineID)
    {
        ControlFile.checkPointCopy.ThisTimeLineID = minXlogTli;
        ControlFile.checkPointCopy.PrevTimeLineID = minXlogTli;
    }

    if (set_wal_segsize != 0)
        ControlFile.xlog_seg_size = WalSegSz;

    if (minXlogSegNo > newXlogSegNo)
        newXlogSegNo = minXlogSegNo;

    /*
     * If we had to guess anything, and -f was not given, just print the
     * guessed values and exit.  Also print if -n is given.
     */
    if ((guessed && !force) || noupdate)
    {
        PrintNewControlValues();
        if (!noupdate)
        {
            printf(_("\nIf these values seem acceptable, use -f to force reset.\n"));
            exit(1);
        }
        else
            exit(0);
    }

    /*
     * Don't reset from a dirty pg_control without -f, either.
     */
    if (ControlFile.state != DB_SHUTDOWNED && !force)
    {
        printf(_("The database server was not shut down cleanly.\n"
                 "Resetting the write-ahead log might cause data to be lost.\n"
                 "If you want to proceed anyway, use -f to force reset.\n"));
        exit(1);
    }

    /*
     * Else, do the dirty deed.
     */
    RewriteControlFile();
    KillExistingXLOG();
    KillExistingArchiveStatus();
    WriteEmptyXLOG();

    printf(_("Write-ahead log reset\n"));
    return 0;
}


/*
 * Look at the version string stored in PG_VERSION and decide if this utility
 * can be run safely or not.
 *
 * We don't want to inject pg_control and WAL files that are for a different
 * major version; that can't do anything good.  Note that we don't treat
 * mismatching version info in pg_control as a reason to bail out, because
 * recovering from a corrupted pg_control is one of the main reasons for this
 * program to exist at all.  However, PG_VERSION is unlikely to get corrupted,
 * and if it were it would be easy to fix by hand.  So let's make this check
 * to prevent simple user errors.
 */
static void
CheckDataVersion(void)
{
    const char *ver_file = "PG_VERSION";
    FILE       *ver_fd;
    char        rawline[64];
    int         len;

    if ((ver_fd = fopen(ver_file, "r")) == NULL)
    {
        fprintf(stderr, _("%s: could not open file \"%s\" for reading: %s\n"),
                progname, ver_file, strerror(errno));
        exit(1);
    }

    /* version number has to be the first line read */
    if (!fgets(rawline, sizeof(rawline), ver_fd))
    {
        if (!ferror(ver_fd))
        {
            fprintf(stderr, _("%s: unexpected empty file \"%s\"\n"),
                    progname, ver_file);
        }
        else
        {
            fprintf(stderr, _("%s: could not read file \"%s\": %s\n"),
                    progname, ver_file, strerror(errno));
        }
        exit(1);
    }

    /* remove trailing newline, handling Windows newlines as well */
    len = strlen(rawline);
    if (len > 0 && rawline[len - 1] == '\n')
    {
        rawline[--len] = '\0';
        if (len > 0 && rawline[len - 1] == '\r')
            rawline[--len] = '\0';
    }

    if (strcmp(rawline, PG_MAJORVERSION) != 0)
    {
        fprintf(stderr, _("%s: data directory is of wrong version\n"
                          "File \"%s\" contains \"%s\", which is not compatible with this program's version \"%s\".\n"),
                progname, ver_file, rawline, PG_MAJORVERSION);
        exit(1);
    }

    fclose(ver_fd);
}


/*
 * Try to read the existing pg_control file.
 *
 * This routine is also responsible for updating old pg_control versions
 * to the current format.  (Currently we don't do anything of the sort.)
 */
static bool
ReadControlFile(void)
{
    int         fd;
    int         len;
    char       *buffer;
    pg_crc32c   crc;

    if ((fd = open(XLOG_CONTROL_FILE, O_RDONLY | PG_BINARY, 0)) < 0)
    {
        /*
         * If pg_control is not there at all, or we can't read it, the odds
         * are we've been handed a bad DataDir path, so give up. User can do
         * "touch pg_control" to force us to proceed.
         */
        fprintf(stderr, _("%s: could not open file \"%s\" for reading: %s\n"),
                progname, XLOG_CONTROL_FILE, strerror(errno));
        if (errno == ENOENT)
            fprintf(stderr, _("If you are sure the data directory path is correct, execute\n"
                              "  touch %s\n"
                              "and try again.\n"),
                    XLOG_CONTROL_FILE);
        exit(1);
    }

    /* Use malloc to ensure we have a maxaligned buffer */
    buffer = (char *) pg_malloc(PG_CONTROL_FILE_SIZE);

    len = read(fd, buffer, PG_CONTROL_FILE_SIZE);
    if (len < 0)
    {
        fprintf(stderr, _("%s: could not read file \"%s\": %s\n"),
                progname, XLOG_CONTROL_FILE, strerror(errno));
        exit(1);
    }
    close(fd);

    if (len >= sizeof(ControlFileData) &&
        ((ControlFileData *) buffer)->pg_control_version == PG_CONTROL_VERSION)
    {
        /* Check the CRC. */
        INIT_CRC32C(crc);
        COMP_CRC32C(crc,
                    buffer,
                    offsetof(ControlFileData, crc));
        FIN_CRC32C(crc);

        if (!EQ_CRC32C(crc, ((ControlFileData *) buffer)->crc))
        {
            /* We will use the data but treat it as guessed. */
            fprintf(stderr,
                    _("%s: pg_control exists but has invalid CRC; proceed with caution\n"),
                    progname);
            guessed = true;
        }

        memcpy(&ControlFile, buffer, sizeof(ControlFile));

        /* return false if WAL segment size is not valid */
        if (!IsValidWalSegSize(ControlFile.xlog_seg_size))
        {
            fprintf(stderr,
                    ngettext("%s: pg_control specifies invalid WAL segment size (%d byte); proceed with caution\n",
                             "%s: pg_control specifies invalid WAL segment size (%d bytes); proceed with caution\n",
                             ControlFile.xlog_seg_size),
                    progname, ControlFile.xlog_seg_size);
            return false;
        }

        return true;
    }

    /* Looks like it's a mess. */
    fprintf(stderr, _("%s: pg_control exists but is broken or wrong version; ignoring it\n"),
            progname);
    return false;
}


/*
 * Guess at pg_control values when we can't read the old ones.
 */
static void
GuessControlValues(void)
{
    uint64      sysidentifier;
    struct timeval tv;

    /*
     * Set up a completely default set of pg_control values.
     */
    guessed = true;
    memset(&ControlFile, 0, sizeof(ControlFile));

    ControlFile.pg_control_version = PG_CONTROL_VERSION;
    ControlFile.catalog_version_no = CATALOG_VERSION_NO;

    /*
     * Create a new unique installation identifier, since we can no longer use
     * any old XLOG records.  See notes in xlog.c about the algorithm.
     */
    gettimeofday(&tv, NULL);
    sysidentifier = ((uint64) tv.tv_sec) << 32;
    sysidentifier |= ((uint64) tv.tv_usec) << 12;
    sysidentifier |= getpid() & 0xFFF;

    ControlFile.system_identifier = sysidentifier;

    ControlFile.checkPointCopy.redo = SizeOfXLogLongPHD;
    ControlFile.checkPointCopy.ThisTimeLineID = 1;
    ControlFile.checkPointCopy.PrevTimeLineID = 1;
    ControlFile.checkPointCopy.fullPageWrites = false;
    ControlFile.checkPointCopy.nextXidEpoch = 0;
    ControlFile.checkPointCopy.nextXid = FirstNormalTransactionId;
    ControlFile.checkPointCopy.nextOid = FirstBootstrapObjectId;
    ControlFile.checkPointCopy.nextMulti = FirstMultiXactId;
    ControlFile.checkPointCopy.nextMultiOffset = 0;
    ControlFile.checkPointCopy.oldestXid = FirstNormalTransactionId;
    ControlFile.checkPointCopy.oldestXidDB = InvalidOid;
    ControlFile.checkPointCopy.oldestMulti = FirstMultiXactId;
    ControlFile.checkPointCopy.oldestMultiDB = InvalidOid;
    ControlFile.checkPointCopy.time = (pg_time_t) time(NULL);
    ControlFile.checkPointCopy.oldestActiveXid = InvalidTransactionId;

    ControlFile.state = DB_SHUTDOWNED;
    ControlFile.time = (pg_time_t) time(NULL);
    ControlFile.checkPoint = ControlFile.checkPointCopy.redo;
    ControlFile.unloggedLSN = 1;

    /* minRecoveryPoint, backupStartPoint and backupEndPoint can be left zero */

    ControlFile.wal_level = WAL_LEVEL_MINIMAL;
    ControlFile.wal_log_hints = false;
    ControlFile.track_commit_timestamp = false;
    ControlFile.MaxConnections = 100;
    ControlFile.max_worker_processes = 8;
    ControlFile.max_prepared_xacts = 0;
    ControlFile.max_locks_per_xact = 64;

    ControlFile.maxAlign = MAXIMUM_ALIGNOF;
    ControlFile.floatFormat = FLOATFORMAT_VALUE;
    ControlFile.blcksz = BLCKSZ;
    ControlFile.relseg_size = RELSEG_SIZE;
    ControlFile.xlog_blcksz = XLOG_BLCKSZ;
    ControlFile.xlog_seg_size = DEFAULT_XLOG_SEG_SIZE;
    ControlFile.nameDataLen = NAMEDATALEN;
    ControlFile.indexMaxKeys = INDEX_MAX_KEYS;
    ControlFile.toast_max_chunk_size = TOAST_MAX_CHUNK_SIZE;
    ControlFile.loblksize = LOBLKSIZE;
    ControlFile.float4ByVal = FLOAT4PASSBYVAL;
    ControlFile.float8ByVal = FLOAT8PASSBYVAL;

    /*
     * XXX eventually, should try to grovel through old XLOG to develop more
     * accurate values for TimeLineID, nextXID, etc.
     */
}


/*
 * Print the guessed pg_control values when we had to guess.
 *
 * NB: this display should be just those fields that will not be
 * reset by RewriteControlFile().
 */
static void
PrintControlValues(bool guessed)
{
    char        sysident_str[32];

    if (guessed)
        printf(_("Guessed pg_control values:\n\n"));
    else
        printf(_("Current pg_control values:\n\n"));

    /*
     * Format system_identifier separately to keep platform-dependent format
     * code out of the translatable message string.
     */
    snprintf(sysident_str, sizeof(sysident_str), UINT64_FORMAT,
             ControlFile.system_identifier);

    printf(_("pg_control version number:            %u\n"),
           ControlFile.pg_control_version);
    printf(_("Catalog version number:               %u\n"),
           ControlFile.catalog_version_no);
    printf(_("Database system identifier:           %s\n"),
           sysident_str);
    printf(_("Latest checkpoint's TimeLineID:       %u\n"),
           ControlFile.checkPointCopy.ThisTimeLineID);
    printf(_("Latest checkpoint's full_page_writes: %s\n"),
           ControlFile.checkPointCopy.fullPageWrites ? _("on") : _("off"));
    printf(_("Latest checkpoint's NextXID:          %u:%u\n"),
           ControlFile.checkPointCopy.nextXidEpoch,
           ControlFile.checkPointCopy.nextXid);
    printf(_("Latest checkpoint's NextOID:          %u\n"),
           ControlFile.checkPointCopy.nextOid);
    printf(_("Latest checkpoint's NextMultiXactId:  %u\n"),
           ControlFile.checkPointCopy.nextMulti);
    printf(_("Latest checkpoint's NextMultiOffset:  %u\n"),
           ControlFile.checkPointCopy.nextMultiOffset);
    printf(_("Latest checkpoint's oldestXID:        %u\n"),
           ControlFile.checkPointCopy.oldestXid);
    printf(_("Latest checkpoint's oldestXID's DB:   %u\n"),
           ControlFile.checkPointCopy.oldestXidDB);
    printf(_("Latest checkpoint's oldestActiveXID:  %u\n"),
           ControlFile.checkPointCopy.oldestActiveXid);
    printf(_("Latest checkpoint's oldestMultiXid:   %u\n"),
           ControlFile.checkPointCopy.oldestMulti);
    printf(_("Latest checkpoint's oldestMulti's DB: %u\n"),
           ControlFile.checkPointCopy.oldestMultiDB);
    printf(_("Latest checkpoint's oldestCommitTsXid:%u\n"),
           ControlFile.checkPointCopy.oldestCommitTsXid);
    printf(_("Latest checkpoint's newestCommitTsXid:%u\n"),
           ControlFile.checkPointCopy.newestCommitTsXid);
    printf(_("Maximum data alignment:               %u\n"),
           ControlFile.maxAlign);
    /* we don't print floatFormat since can't say much useful about it */
    printf(_("Database block size:                  %u\n"),
           ControlFile.blcksz);
    printf(_("Blocks per segment of large relation: %u\n"),
           ControlFile.relseg_size);
    printf(_("WAL block size:                       %u\n"),
           ControlFile.xlog_blcksz);
    printf(_("Bytes per WAL segment:                %u\n"),
           ControlFile.xlog_seg_size);
    printf(_("Maximum length of identifiers:        %u\n"),
           ControlFile.nameDataLen);
    printf(_("Maximum columns in an index:          %u\n"),
           ControlFile.indexMaxKeys);
    printf(_("Maximum size of a TOAST chunk:        %u\n"),
           ControlFile.toast_max_chunk_size);
    printf(_("Size of a large-object chunk:         %u\n"),
           ControlFile.loblksize);
    /* This is no longer configurable, but users may still expect to see it: */
    printf(_("Date/time type storage:               %s\n"),
           _("64-bit integers"));
    printf(_("Float4 argument passing:              %s\n"),
           (ControlFile.float4ByVal ? _("by value") : _("by reference")));
    printf(_("Float8 argument passing:              %s\n"),
           (ControlFile.float8ByVal ? _("by value") : _("by reference")));
    printf(_("Data page checksum version:           %u\n"),
           ControlFile.data_checksum_version);
}


/*
 * Print the values to be changed.
 */
static void
PrintNewControlValues(void)
{
    char        fname[MAXFNAMELEN];

    /* This will be always printed in order to keep format same. */
    printf(_("\n\nValues to be changed:\n\n"));

    XLogFileName(fname, ControlFile.checkPointCopy.ThisTimeLineID,
                 newXlogSegNo, WalSegSz);
    printf(_("First log segment after reset:        %s\n"), fname);

    if (set_mxid != 0)
    {
        printf(_("NextMultiXactId:                      %u\n"),
               ControlFile.checkPointCopy.nextMulti);
        printf(_("OldestMultiXid:                       %u\n"),
               ControlFile.checkPointCopy.oldestMulti);
        printf(_("OldestMulti's DB:                     %u\n"),
               ControlFile.checkPointCopy.oldestMultiDB);
    }

    if (set_mxoff != -1)
    {
        printf(_("NextMultiOffset:                      %u\n"),
               ControlFile.checkPointCopy.nextMultiOffset);
    }

    if (set_oid != 0)
    {
        printf(_("NextOID:                              %u\n"),
               ControlFile.checkPointCopy.nextOid);
    }

    if (set_xid != 0)
    {
        printf(_("NextXID:                              %u\n"),
               ControlFile.checkPointCopy.nextXid);
        printf(_("OldestXID:                            %u\n"),
               ControlFile.checkPointCopy.oldestXid);
        printf(_("OldestXID's DB:                       %u\n"),
               ControlFile.checkPointCopy.oldestXidDB);
    }

    if (set_xid_epoch != -1)
    {
        printf(_("NextXID epoch:                        %u\n"),
               ControlFile.checkPointCopy.nextXidEpoch);
    }

    if (set_oldest_commit_ts_xid != 0)
    {
        printf(_("oldestCommitTsXid:                    %u\n"),
               ControlFile.checkPointCopy.oldestCommitTsXid);
    }
    if (set_newest_commit_ts_xid != 0)
    {
        printf(_("newestCommitTsXid:                    %u\n"),
               ControlFile.checkPointCopy.newestCommitTsXid);
    }

    if (set_wal_segsize != 0)
    {
        printf(_("Bytes per WAL segment:                %u\n"),
               ControlFile.xlog_seg_size);
    }
}


/*
 * Write out the new pg_control file.
 */
static void
RewriteControlFile(void)
{
    int         fd;
    char        buffer[PG_CONTROL_FILE_SIZE];   /* need not be aligned */

    /*
     * For good luck, apply the same static assertions as in backend's
     * WriteControlFile().
     */
    StaticAssertStmt(sizeof(ControlFileData) <= PG_CONTROL_MAX_SAFE_SIZE,
                     "pg_control is too large for atomic disk writes");
    StaticAssertStmt(sizeof(ControlFileData) <= PG_CONTROL_FILE_SIZE,
                     "sizeof(ControlFileData) exceeds PG_CONTROL_FILE_SIZE");

    /*
     * Adjust fields as needed to force an empty XLOG starting at
     * newXlogSegNo.
     */
    XLogSegNoOffsetToRecPtr(newXlogSegNo, SizeOfXLogLongPHD,
                            ControlFile.checkPointCopy.redo, WalSegSz);
    ControlFile.checkPointCopy.time = (pg_time_t) time(NULL);

    ControlFile.state = DB_SHUTDOWNED;
    ControlFile.time = (pg_time_t) time(NULL);
    ControlFile.checkPoint = ControlFile.checkPointCopy.redo;
    ControlFile.minRecoveryPoint = 0;
    ControlFile.minRecoveryPointTLI = 0;
    ControlFile.backupStartPoint = 0;
    ControlFile.backupEndPoint = 0;
    ControlFile.backupEndRequired = false;

    /*
     * Force the defaults for max_* settings. The values don't really matter
     * as long as wal_level='minimal'; the postmaster will reset these fields
     * anyway at startup.
     */
    ControlFile.wal_level = WAL_LEVEL_MINIMAL;
    ControlFile.wal_log_hints = false;
    ControlFile.track_commit_timestamp = false;
    ControlFile.MaxConnections = 100;
    ControlFile.max_worker_processes = 8;
    ControlFile.max_prepared_xacts = 0;
    ControlFile.max_locks_per_xact = 64;

    /* Contents are protected with a CRC */
    INIT_CRC32C(ControlFile.crc);
    COMP_CRC32C(ControlFile.crc,
                (char *) &ControlFile,
                offsetof(ControlFileData, crc));
    FIN_CRC32C(ControlFile.crc);

    /*
     * We write out PG_CONTROL_FILE_SIZE bytes into pg_control, zero-padding
     * the excess over sizeof(ControlFileData).  This reduces the odds of
     * premature-EOF errors when reading pg_control.  We'll still fail when we
     * check the contents of the file, but hopefully with a more specific
     * error than "couldn't read pg_control".
     */
    memset(buffer, 0, PG_CONTROL_FILE_SIZE);
    memcpy(buffer, &ControlFile, sizeof(ControlFileData));

    unlink(XLOG_CONTROL_FILE);

    fd = open(XLOG_CONTROL_FILE,
              O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
              pg_file_create_mode);
    if (fd < 0)
    {
        fprintf(stderr, _("%s: could not create pg_control file: %s\n"),
                progname, strerror(errno));
        exit(1);
    }

    errno = 0;
    if (write(fd, buffer, PG_CONTROL_FILE_SIZE) != PG_CONTROL_FILE_SIZE)
    {
        /* if write didn't set errno, assume problem is no disk space */
        if (errno == 0)
            errno = ENOSPC;
        fprintf(stderr, _("%s: could not write pg_control file: %s\n"),
                progname, strerror(errno));
        exit(1);
    }

    if (fsync(fd) != 0)
    {
        fprintf(stderr, _("%s: fsync error: %s\n"), progname, strerror(errno));
        exit(1);
    }

    close(fd);
}


/*
 * Scan existing XLOG files and determine the highest existing WAL address
 *
 * On entry, ControlFile.checkPointCopy.redo and ControlFile.xlog_seg_size
 * are assumed valid (note that we allow the old xlog seg size to differ
 * from what we're using).  On exit, newXlogId and newXlogSeg are set to
 * suitable values for the beginning of replacement WAL (in our seg size).
 */
static void
FindEndOfXLOG(void)
{
    DIR        *xldir;
    struct dirent *xlde;
    uint64      segs_per_xlogid;
    uint64      xlogbytepos;

    /*
     * Initialize the max() computation using the last checkpoint address from
     * old pg_control.  Note that for the moment we are working with segment
     * numbering according to the old xlog seg size.
     */
    segs_per_xlogid = (UINT64CONST(0x0000000100000000) / ControlFile.xlog_seg_size);
    newXlogSegNo = ControlFile.checkPointCopy.redo / ControlFile.xlog_seg_size;

    /*
     * Scan the pg_wal directory to find existing WAL segment files. We assume
     * any present have been used; in most scenarios this should be
     * conservative, because of xlog.c's attempts to pre-create files.
     */
    xldir = opendir(XLOGDIR);
    if (xldir == NULL)
    {
        fprintf(stderr, _("%s: could not open directory \"%s\": %s\n"),
                progname, XLOGDIR, strerror(errno));
        exit(1);
    }

    while (errno = 0, (xlde = readdir(xldir)) != NULL)
    {
        if (IsXLogFileName(xlde->d_name) ||
            IsPartialXLogFileName(xlde->d_name))
        {
            unsigned int tli,
                        log,
                        seg;
            XLogSegNo   segno;

            /*
             * Note: We don't use XLogFromFileName here, because we want to
             * use the segment size from the control file, not the size the
             * pg_resetwal binary was compiled with
             */
            sscanf(xlde->d_name, "%08X%08X%08X", &tli, &log, &seg);
            segno = ((uint64) log) * segs_per_xlogid + seg;

            /*
             * Note: we take the max of all files found, regardless of their
             * timelines.  Another possibility would be to ignore files of
             * timelines other than the target TLI, but this seems safer.
             * Better too large a result than too small...
             */
            if (segno > newXlogSegNo)
                newXlogSegNo = segno;
        }
    }

    if (errno)
    {
        fprintf(stderr, _("%s: could not read directory \"%s\": %s\n"),
                progname, XLOGDIR, strerror(errno));
        exit(1);
    }

    if (closedir(xldir))
    {
        fprintf(stderr, _("%s: could not close directory \"%s\": %s\n"),
                progname, XLOGDIR, strerror(errno));
        exit(1);
    }

    /*
     * Finally, convert to new xlog seg size, and advance by one to ensure we
     * are in virgin territory.
     */
    xlogbytepos = newXlogSegNo * ControlFile.xlog_seg_size;
    newXlogSegNo = (xlogbytepos + ControlFile.xlog_seg_size - 1) / WalSegSz;
    newXlogSegNo++;
}


/*
 * Remove existing XLOG files
 */
static void
KillExistingXLOG(void)
{
    DIR        *xldir;
    struct dirent *xlde;
    char        path[MAXPGPATH + sizeof(XLOGDIR)];

    xldir = opendir(XLOGDIR);
    if (xldir == NULL)
    {
        fprintf(stderr, _("%s: could not open directory \"%s\": %s\n"),
                progname, XLOGDIR, strerror(errno));
        exit(1);
    }

    while (errno = 0, (xlde = readdir(xldir)) != NULL)
    {
        if (IsXLogFileName(xlde->d_name) ||
            IsPartialXLogFileName(xlde->d_name))
        {
            snprintf(path, sizeof(path), "%s/%s", XLOGDIR, xlde->d_name);
            if (unlink(path) < 0)
            {
                fprintf(stderr, _("%s: could not delete file \"%s\": %s\n"),
                        progname, path, strerror(errno));
                exit(1);
            }
        }
    }

    if (errno)
    {
        fprintf(stderr, _("%s: could not read directory \"%s\": %s\n"),
                progname, XLOGDIR, strerror(errno));
        exit(1);
    }

    if (closedir(xldir))
    {
        fprintf(stderr, _("%s: could not close directory \"%s\": %s\n"),
                progname, XLOGDIR, strerror(errno));
        exit(1);
    }
}


/*
 * Remove existing archive status files
 */
static void
KillExistingArchiveStatus(void)
{
#define ARCHSTATDIR XLOGDIR "/archive_status"

    DIR        *xldir;
    struct dirent *xlde;
    char        path[MAXPGPATH + sizeof(ARCHSTATDIR)];

    xldir = opendir(ARCHSTATDIR);
    if (xldir == NULL)
    {
        fprintf(stderr, _("%s: could not open directory \"%s\": %s\n"),
                progname, ARCHSTATDIR, strerror(errno));
        exit(1);
    }

    while (errno = 0, (xlde = readdir(xldir)) != NULL)
    {
        if (strspn(xlde->d_name, "0123456789ABCDEF") == XLOG_FNAME_LEN &&
            (strcmp(xlde->d_name + XLOG_FNAME_LEN, ".ready") == 0 ||
             strcmp(xlde->d_name + XLOG_FNAME_LEN, ".done") == 0 ||
             strcmp(xlde->d_name + XLOG_FNAME_LEN, ".partial.ready") == 0 ||
             strcmp(xlde->d_name + XLOG_FNAME_LEN, ".partial.done") == 0))
        {
            snprintf(path, sizeof(path), "%s/%s", ARCHSTATDIR, xlde->d_name);
            if (unlink(path) < 0)
            {
                fprintf(stderr, _("%s: could not delete file \"%s\": %s\n"),
                        progname, path, strerror(errno));
                exit(1);
            }
        }
    }

    if (errno)
    {
        fprintf(stderr, _("%s: could not read directory \"%s\": %s\n"),
                progname, ARCHSTATDIR, strerror(errno));
        exit(1);
    }

    if (closedir(xldir))
    {
        fprintf(stderr, _("%s: could not close directory \"%s\": %s\n"),
                progname, ARCHSTATDIR, strerror(errno));
        exit(1);
    }
}


/*
 * Write an empty XLOG file, containing only the checkpoint record
 * already set up in ControlFile.
 */
static void
WriteEmptyXLOG(void)
{
    char       *buffer;
    XLogPageHeader page;
    XLogLongPageHeader longpage;
    XLogRecord *record;
    pg_crc32c   crc;
    char        path[MAXPGPATH];
    int         fd;
    int         nbytes;
    char       *recptr;

    /* Use malloc() to ensure buffer is MAXALIGNED */
    buffer = (char *) pg_malloc(XLOG_BLCKSZ);
    page = (XLogPageHeader) buffer;
    memset(buffer, 0, XLOG_BLCKSZ);

    /* Set up the XLOG page header */
    page->xlp_magic = XLOG_PAGE_MAGIC;
    page->xlp_info = XLP_LONG_HEADER;
    page->xlp_tli = ControlFile.checkPointCopy.ThisTimeLineID;
    page->xlp_pageaddr = ControlFile.checkPointCopy.redo - SizeOfXLogLongPHD;
    longpage = (XLogLongPageHeader) page;
    longpage->xlp_sysid = ControlFile.system_identifier;
    longpage->xlp_seg_size = WalSegSz;
    longpage->xlp_xlog_blcksz = XLOG_BLCKSZ;

    /* Insert the initial checkpoint record */
    recptr = (char *) page + SizeOfXLogLongPHD;
    record = (XLogRecord *) recptr;
    record->xl_prev = 0;
    record->xl_xid = InvalidTransactionId;
    record->xl_tot_len = SizeOfXLogRecord + SizeOfXLogRecordDataHeaderShort + sizeof(CheckPoint);
    record->xl_info = XLOG_CHECKPOINT_SHUTDOWN;
    record->xl_rmid = RM_XLOG_ID;

    recptr += SizeOfXLogRecord;
    *(recptr++) = (char) XLR_BLOCK_ID_DATA_SHORT;
    *(recptr++) = sizeof(CheckPoint);
    memcpy(recptr, &ControlFile.checkPointCopy,
           sizeof(CheckPoint));

    INIT_CRC32C(crc);
    COMP_CRC32C(crc, ((char *) record) + SizeOfXLogRecord, record->xl_tot_len - SizeOfXLogRecord);
    COMP_CRC32C(crc, (char *) record, offsetof(XLogRecord, xl_crc));
    FIN_CRC32C(crc);
    record->xl_crc = crc;

    /* Write the first page */
    XLogFilePath(path, ControlFile.checkPointCopy.ThisTimeLineID,
                 newXlogSegNo, WalSegSz);

    unlink(path);

    fd = open(path, O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
              pg_file_create_mode);
    if (fd < 0)
    {
        fprintf(stderr, _("%s: could not open file \"%s\": %s\n"),
                progname, path, strerror(errno));
        exit(1);
    }

    errno = 0;
    if (write(fd, buffer, XLOG_BLCKSZ) != XLOG_BLCKSZ)
    {
        /* if write didn't set errno, assume problem is no disk space */
        if (errno == 0)
            errno = ENOSPC;
        fprintf(stderr, _("%s: could not write file \"%s\": %s\n"),
                progname, path, strerror(errno));
        exit(1);
    }

    /* Fill the rest of the file with zeroes */
    memset(buffer, 0, XLOG_BLCKSZ);
    for (nbytes = XLOG_BLCKSZ; nbytes < WalSegSz; nbytes += XLOG_BLCKSZ)
    {
        errno = 0;
        if (write(fd, buffer, XLOG_BLCKSZ) != XLOG_BLCKSZ)
        {
            if (errno == 0)
                errno = ENOSPC;
            fprintf(stderr, _("%s: could not write file \"%s\": %s\n"),
                    progname, path, strerror(errno));
            exit(1);
        }
    }

    if (fsync(fd) != 0)
    {
        fprintf(stderr, _("%s: fsync error: %s\n"), progname, strerror(errno));
        exit(1);
    }

    close(fd);
}


static void
usage(void)
{
    printf(_("%s resets the PostgreSQL write-ahead log.\n\n"), progname);
    printf(_("Usage:\n  %s [OPTION]... DATADIR\n\n"), progname);
    printf(_("Options:\n"));
    printf(_("  -c, --commit-timestamp-ids=XID,XID\n"
             "                                 set oldest and newest transactions bearing\n"
             "                                 commit timestamp (zero means no change)\n"));
    printf(_(" [-D, --pgdata=]DATADIR          data directory\n"));
    printf(_("  -e, --epoch=XIDEPOCH           set next transaction ID epoch\n"));
    printf(_("  -f, --force                    force update to be done\n"));
    printf(_("  -l, --next-wal-file=WALFILE    set minimum starting location for new WAL\n"));
    printf(_("  -m, --multixact-ids=MXID,MXID  set next and oldest multitransaction ID\n"));
    printf(_("  -n, --dry-run                  no update, just show what would be done\n"));
    printf(_("  -o, --next-oid=OID             set next OID\n"));
    printf(_("  -O, --multixact-offset=OFFSET  set next multitransaction offset\n"));
    printf(_("  -V, --version                  output version information, then exit\n"));
    printf(_("  -x, --next-transaction-id=XID  set next transaction ID\n"));
    printf(_("      --wal-segsize=SIZE         size of WAL segments, in megabytes\n"));
    printf(_("  -?, --help                     show this help, then exit\n"));
    printf(_("\nReport bugs to <pgsql-bugs@postgresql.org>.\n"));
}