pgarch.c

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/*-------------------------------------------------------------------------
 *
 * pgarch.c
 *
 *  PostgreSQL WAL archiver
 *
 *  All functions relating to archiver are included here
 *
 *  - All functions executed by archiver process
 *
 *  - archiver is forked from postmaster, and the two
 *  processes then communicate using signals. All functions
 *  executed by postmaster are included in this file.
 *
 *  Initial author: Simon Riggs     simon@2ndquadrant.com
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/postmaster/pgarch.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

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

#include "access/xlog.h"
#include "access/xlog_internal.h"
#include "libpq/pqsignal.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/fork_process.h"
#include "postmaster/interrupt.h"
#include "postmaster/pgarch.h"
#include "postmaster/postmaster.h"
#include "storage/dsm.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/latch.h"
#include "storage/pg_shmem.h"
#include "storage/pmsignal.h"
#include "utils/guc.h"
#include "utils/ps_status.h"


/* ----------
 * Timer definitions.
 * ----------
 */
#define PGARCH_AUTOWAKE_INTERVAL 60 /* How often to force a poll of the
                                     * archive status directory; in seconds. */
#define PGARCH_RESTART_INTERVAL 10  /* How often to attempt to restart a
                                     * failed archiver; in seconds. */

/*
 * Maximum number of retries allowed when attempting to archive a WAL
 * file.
 */
#define NUM_ARCHIVE_RETRIES 3

/*
 * Maximum number of retries allowed when attempting to remove an
 * orphan archive status file.
 */
#define NUM_ORPHAN_CLEANUP_RETRIES 3


/* ----------
 * Local data
 * ----------
 */
static time_t last_pgarch_start_time;
static time_t last_sigterm_time = 0;

/*
 * Flags set by interrupt handlers for later service in the main loop.
 */
static volatile sig_atomic_t wakened = false;
static volatile sig_atomic_t ready_to_stop = false;

/* ----------
 * Local function forward declarations
 * ----------
 */
#ifdef EXEC_BACKEND
static pid_t pgarch_forkexec(void);
#endif

NON_EXEC_STATIC void PgArchiverMain(int argc, char *argv[]) pg_attribute_noreturn();
static void pgarch_waken(SIGNAL_ARGS);
static void pgarch_waken_stop(SIGNAL_ARGS);
static void pgarch_MainLoop(void);
static void pgarch_ArchiverCopyLoop(void);
static bool pgarch_archiveXlog(char *xlog);
static bool pgarch_readyXlog(char *xlog);
static void pgarch_archiveDone(char *xlog);


/* ------------------------------------------------------------
 * Public functions called from postmaster follow
 * ------------------------------------------------------------
 */

/*
 * pgarch_start
 *
 *  Called from postmaster at startup or after an existing archiver
 *  died.  Attempt to fire up a fresh archiver process.
 *
 *  Returns PID of child process, or 0 if fail.
 *
 *  Note: if fail, we will be called again from the postmaster main loop.
 */
int
pgarch_start(void)
{
    time_t      curtime;
    pid_t       pgArchPid;

    /*
     * Do nothing if no archiver needed
     */
    if (!XLogArchivingActive())
        return 0;

    /*
     * Do nothing if too soon since last archiver start.  This is a safety
     * valve to protect against continuous respawn attempts if the archiver is
     * dying immediately at launch. Note that since we will be re-called from
     * the postmaster main loop, we will get another chance later.
     */
    curtime = time(NULL);
    if ((unsigned int) (curtime - last_pgarch_start_time) <
        (unsigned int) PGARCH_RESTART_INTERVAL)
        return 0;
    last_pgarch_start_time = curtime;

#ifdef EXEC_BACKEND
    switch ((pgArchPid = pgarch_forkexec()))
#else
    switch ((pgArchPid = fork_process()))
#endif
    {
        case -1:
            ereport(LOG,
                    (errmsg("could not fork archiver: %m")));
            return 0;

#ifndef EXEC_BACKEND
        case 0:
            /* in postmaster child ... */
            InitPostmasterChild();

            /* Close the postmaster's sockets */
            ClosePostmasterPorts(false);

            /* Drop our connection to postmaster's shared memory, as well */
            dsm_detach_all();
            PGSharedMemoryDetach();

            PgArchiverMain(0, NULL);
            break;
#endif

        default:
            return (int) pgArchPid;
    }

    /* shouldn't get here */
    return 0;
}

/* ------------------------------------------------------------
 * Local functions called by archiver follow
 * ------------------------------------------------------------
 */


#ifdef EXEC_BACKEND

/*
 * pgarch_forkexec() -
 *
 * Format up the arglist for, then fork and exec, archive process
 */
static pid_t
pgarch_forkexec(void)
{
    char       *av[10];
    int         ac = 0;

    av[ac++] = "postgres";

    av[ac++] = "--forkarch";

    av[ac++] = NULL;            /* filled in by postmaster_forkexec */

    av[ac] = NULL;
    Assert(ac < lengthof(av));

    return postmaster_forkexec(ac, av);
}
#endif                          /* EXEC_BACKEND */


/*
 * PgArchiverMain
 *
 *  The argc/argv parameters are valid only in EXEC_BACKEND case.  However,
 *  since we don't use 'em, it hardly matters...
 */
NON_EXEC_STATIC void
PgArchiverMain(int argc, char *argv[])
{
    /*
     * Ignore all signals usually bound to some action in the postmaster,
     * except for SIGHUP, SIGTERM, SIGUSR1, SIGUSR2, and SIGQUIT.
     */
    pqsignal(SIGHUP, SignalHandlerForConfigReload);
    pqsignal(SIGINT, SIG_IGN);
    pqsignal(SIGTERM, SignalHandlerForShutdownRequest);
    /* SIGQUIT handler was already set up by InitPostmasterChild */
    pqsignal(SIGALRM, SIG_IGN);
    pqsignal(SIGPIPE, SIG_IGN);
    pqsignal(SIGUSR1, pgarch_waken);
    pqsignal(SIGUSR2, pgarch_waken_stop);
    /* Reset some signals that are accepted by postmaster but not here */
    pqsignal(SIGCHLD, SIG_DFL);
    PG_SETMASK(&UnBlockSig);

    MyBackendType = B_ARCHIVER;
    init_ps_display(NULL);

    pgarch_MainLoop();

    exit(0);
}

/* SIGUSR1 signal handler for archiver process */
static void
pgarch_waken(SIGNAL_ARGS)
{
    int         save_errno = errno;

    /* set flag that there is work to be done */
    wakened = true;
    SetLatch(MyLatch);

    errno = save_errno;
}

/* SIGUSR2 signal handler for archiver process */
static void
pgarch_waken_stop(SIGNAL_ARGS)
{
    int         save_errno = errno;

    /* set flag to do a final cycle and shut down afterwards */
    ready_to_stop = true;
    SetLatch(MyLatch);

    errno = save_errno;
}

/*
 * pgarch_MainLoop
 *
 * Main loop for archiver
 */
static void
pgarch_MainLoop(void)
{
    pg_time_t   last_copy_time = 0;
    bool        time_to_stop;

    /*
     * We run the copy loop immediately upon entry, in case there are
     * unarchived files left over from a previous database run (or maybe the
     * archiver died unexpectedly).  After that we wait for a signal or
     * timeout before doing more.
     */
    wakened = true;

    /*
     * There shouldn't be anything for the archiver to do except to wait for a
     * signal ... however, the archiver exists to protect our data, so she
     * wakes up occasionally to allow herself to be proactive.
     */
    do
    {
        ResetLatch(MyLatch);

        /* When we get SIGUSR2, we do one more archive cycle, then exit */
        time_to_stop = ready_to_stop;

        /* Check for config update */
        if (ConfigReloadPending)
        {
            ConfigReloadPending = false;
            ProcessConfigFile(PGC_SIGHUP);
        }

        /*
         * If we've gotten SIGTERM, we normally just sit and do nothing until
         * SIGUSR2 arrives.  However, that means a random SIGTERM would
         * disable archiving indefinitely, which doesn't seem like a good
         * idea.  If more than 60 seconds pass since SIGTERM, exit anyway, so
         * that the postmaster can start a new archiver if needed.
         */
        if (ShutdownRequestPending)
        {
            time_t      curtime = time(NULL);

            if (last_sigterm_time == 0)
                last_sigterm_time = curtime;
            else if ((unsigned int) (curtime - last_sigterm_time) >=
                     (unsigned int) 60)
                break;
        }

        /* Do what we're here for */
        if (wakened || time_to_stop)
        {
            wakened = false;
            pgarch_ArchiverCopyLoop();
            last_copy_time = time(NULL);
        }

        /*
         * Sleep until a signal is received, or until a poll is forced by
         * PGARCH_AUTOWAKE_INTERVAL having passed since last_copy_time, or
         * until postmaster dies.
         */
        if (!time_to_stop)      /* Don't wait during last iteration */
        {
            pg_time_t   curtime = (pg_time_t) time(NULL);
            int         timeout;

            timeout = PGARCH_AUTOWAKE_INTERVAL - (curtime - last_copy_time);
            if (timeout > 0)
            {
                int         rc;

                rc = WaitLatch(MyLatch,
                               WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
                               timeout * 1000L,
                               WAIT_EVENT_ARCHIVER_MAIN);
                if (rc & WL_TIMEOUT)
                    wakened = true;
                if (rc & WL_POSTMASTER_DEATH)
                    time_to_stop = true;
            }
            else
                wakened = true;
        }

        /*
         * The archiver quits either when the postmaster dies (not expected)
         * or after completing one more archiving cycle after receiving
         * SIGUSR2.
         */
    } while (!time_to_stop);
}

/*
 * pgarch_ArchiverCopyLoop
 *
 * Archives all outstanding xlogs then returns
 */
static void
pgarch_ArchiverCopyLoop(void)
{
    char        xlog[MAX_XFN_CHARS + 1];

    /*
     * loop through all xlogs with archive_status of .ready and archive
     * them...mostly we expect this to be a single file, though it is possible
     * some backend will add files onto the list of those that need archiving
     * while we are still copying earlier archives
     */
    while (pgarch_readyXlog(xlog))
    {
        int         failures = 0;
        int         failures_orphan = 0;

        for (;;)
        {
            struct stat stat_buf;
            char        pathname[MAXPGPATH];

            /*
             * Do not initiate any more archive commands after receiving
             * SIGTERM, nor after the postmaster has died unexpectedly. The
             * first condition is to try to keep from having init SIGKILL the
             * command, and the second is to avoid conflicts with another
             * archiver spawned by a newer postmaster.
             */
            if (ShutdownRequestPending || !PostmasterIsAlive())
                return;

            /*
             * Check for config update.  This is so that we'll adopt a new
             * setting for archive_command as soon as possible, even if there
             * is a backlog of files to be archived.
             */
            if (ConfigReloadPending)
            {
                ConfigReloadPending = false;
                ProcessConfigFile(PGC_SIGHUP);
            }

            /* can't do anything if no command ... */
            if (!XLogArchiveCommandSet())
            {
                ereport(WARNING,
                        (errmsg("archive_mode enabled, yet archive_command is not set")));
                return;
            }

            /*
             * Since archive status files are not removed in a durable manner,
             * a system crash could leave behind .ready files for WAL segments
             * that have already been recycled or removed.  In this case,
             * simply remove the orphan status file and move on.  unlink() is
             * used here as even on subsequent crashes the same orphan files
             * would get removed, so there is no need to worry about
             * durability.
             */
            snprintf(pathname, MAXPGPATH, XLOGDIR "/%s", xlog);
            if (stat(pathname, &stat_buf) != 0 && errno == ENOENT)
            {
                char        xlogready[MAXPGPATH];

                StatusFilePath(xlogready, xlog, ".ready");
                if (unlink(xlogready) == 0)
                {
                    ereport(WARNING,
                            (errmsg("removed orphan archive status file \"%s\"",
                                    xlogready)));

                    /* leave loop and move to the next status file */
                    break;
                }

                if (++failures_orphan >= NUM_ORPHAN_CLEANUP_RETRIES)
                {
                    ereport(WARNING,
                            (errmsg("removal of orphan archive status file \"%s\" failed too many times, will try again later",
                                    xlogready)));

                    /* give up cleanup of orphan status files */
                    return;
                }

                /* wait a bit before retrying */
                pg_usleep(1000000L);
                continue;
            }

            if (pgarch_archiveXlog(xlog))
            {
                /* successful */
                pgarch_archiveDone(xlog);

                /*
                 * Tell the collector about the WAL file that we successfully
                 * archived
                 */
                pgstat_send_archiver(xlog, false);

                break;          /* out of inner retry loop */
            }
            else
            {
                /*
                 * Tell the collector about the WAL file that we failed to
                 * archive
                 */
                pgstat_send_archiver(xlog, true);

                if (++failures >= NUM_ARCHIVE_RETRIES)
                {
                    ereport(WARNING,
                            (errmsg("archiving write-ahead log file \"%s\" failed too many times, will try again later",
                                    xlog)));
                    return;     /* give up archiving for now */
                }
                pg_usleep(1000000L);    /* wait a bit before retrying */
            }
        }
    }
}

/*
 * pgarch_archiveXlog
 *
 * Invokes system(3) to copy one archive file to wherever it should go
 *
 * Returns true if successful
 */
static bool
pgarch_archiveXlog(char *xlog)
{
    char        xlogarchcmd[MAXPGPATH];
    char        pathname[MAXPGPATH];
    char        activitymsg[MAXFNAMELEN + 16];
    char       *dp;
    char       *endp;
    const char *sp;
    int         rc;

    snprintf(pathname, MAXPGPATH, XLOGDIR "/%s", xlog);

    /*
     * construct the command to be executed
     */
    dp = xlogarchcmd;
    endp = xlogarchcmd + MAXPGPATH - 1;
    *endp = '\0';

    for (sp = XLogArchiveCommand; *sp; sp++)
    {
        if (*sp == '%')
        {
            switch (sp[1])
            {
                case 'p':
                    /* %p: relative path of source file */
                    sp++;
                    strlcpy(dp, pathname, endp - dp);
                    make_native_path(dp);
                    dp += strlen(dp);
                    break;
                case 'f':
                    /* %f: filename of source file */
                    sp++;
                    strlcpy(dp, xlog, endp - dp);
                    dp += strlen(dp);
                    break;
                case '%':
                    /* convert %% to a single % */
                    sp++;
                    if (dp < endp)
                        *dp++ = *sp;
                    break;
                default:
                    /* otherwise treat the % as not special */
                    if (dp < endp)
                        *dp++ = *sp;
                    break;
            }
        }
        else
        {
            if (dp < endp)
                *dp++ = *sp;
        }
    }
    *dp = '\0';

    ereport(DEBUG3,
            (errmsg_internal("executing archive command \"%s\"",
                             xlogarchcmd)));

    /* Report archive activity in PS display */
    snprintf(activitymsg, sizeof(activitymsg), "archiving %s", xlog);
    set_ps_display(activitymsg);

    rc = system(xlogarchcmd);
    if (rc != 0)
    {
        /*
         * If either the shell itself, or a called command, died on a signal,
         * abort the archiver.  We do this because system() ignores SIGINT and
         * SIGQUIT while waiting; so a signal is very likely something that
         * should have interrupted us too.  Also die if the shell got a hard
         * "command not found" type of error.  If we overreact it's no big
         * deal, the postmaster will just start the archiver again.
         */
        int         lev = wait_result_is_any_signal(rc, true) ? FATAL : LOG;

        if (WIFEXITED(rc))
        {
            ereport(lev,
                    (errmsg("archive command failed with exit code %d",
                            WEXITSTATUS(rc)),
                     errdetail("The failed archive command was: %s",
                               xlogarchcmd)));
        }
        else if (WIFSIGNALED(rc))
        {
#if defined(WIN32)
            ereport(lev,
                    (errmsg("archive command was terminated by exception 0x%X",
                            WTERMSIG(rc)),
                     errhint("See C include file \"ntstatus.h\" for a description of the hexadecimal value."),
                     errdetail("The failed archive command was: %s",
                               xlogarchcmd)));
#else
            ereport(lev,
                    (errmsg("archive command was terminated by signal %d: %s",
                            WTERMSIG(rc), pg_strsignal(WTERMSIG(rc))),
                     errdetail("The failed archive command was: %s",
                               xlogarchcmd)));
#endif
        }
        else
        {
            ereport(lev,
                    (errmsg("archive command exited with unrecognized status %d",
                            rc),
                     errdetail("The failed archive command was: %s",
                               xlogarchcmd)));
        }

        snprintf(activitymsg, sizeof(activitymsg), "failed on %s", xlog);
        set_ps_display(activitymsg);

        return false;
    }
    elog(DEBUG1, "archived write-ahead log file \"%s\"", xlog);

    snprintf(activitymsg, sizeof(activitymsg), "last was %s", xlog);
    set_ps_display(activitymsg);

    return true;
}

/*
 * pgarch_readyXlog
 *
 * Return name of the oldest xlog file that has not yet been archived.
 * No notification is set that file archiving is now in progress, so
 * this would need to be extended if multiple concurrent archival
 * tasks were created. If a failure occurs, we will completely
 * re-copy the file at the next available opportunity.
 *
 * It is important that we return the oldest, so that we archive xlogs
 * in order that they were written, for two reasons:
 * 1) to maintain the sequential chain of xlogs required for recovery
 * 2) because the oldest ones will sooner become candidates for
 * recycling at time of checkpoint
 *
 * NOTE: the "oldest" comparison will consider any .history file to be older
 * than any other file except another .history file.  Segments on a timeline
 * with a smaller ID will be older than all segments on a timeline with a
 * larger ID; the net result being that past timelines are given higher
 * priority for archiving.  This seems okay, or at least not obviously worth
 * changing.
 */
static bool
pgarch_readyXlog(char *xlog)
{
    /*
     * open xlog status directory and read through list of xlogs that have the
     * .ready suffix, looking for earliest file. It is possible to optimise
     * this code, though only a single file is expected on the vast majority
     * of calls, so....
     */
    char        XLogArchiveStatusDir[MAXPGPATH];
    DIR        *rldir;
    struct dirent *rlde;
    bool        found = false;
    bool        historyFound = false;

    snprintf(XLogArchiveStatusDir, MAXPGPATH, XLOGDIR "/archive_status");
    rldir = AllocateDir(XLogArchiveStatusDir);

    while ((rlde = ReadDir(rldir, XLogArchiveStatusDir)) != NULL)
    {
        int         basenamelen = (int) strlen(rlde->d_name) - 6;
        char        basename[MAX_XFN_CHARS + 1];
        bool        ishistory;

        /* Ignore entries with unexpected number of characters */
        if (basenamelen < MIN_XFN_CHARS ||
            basenamelen > MAX_XFN_CHARS)
            continue;

        /* Ignore entries with unexpected characters */
        if (strspn(rlde->d_name, VALID_XFN_CHARS) < basenamelen)
            continue;

        /* Ignore anything not suffixed with .ready */
        if (strcmp(rlde->d_name + basenamelen, ".ready") != 0)
            continue;

        /* Truncate off the .ready */
        memcpy(basename, rlde->d_name, basenamelen);
        basename[basenamelen] = '\0';

        /* Is this a history file? */
        ishistory = IsTLHistoryFileName(basename);

        /*
         * Consume the file to archive.  History files have the highest
         * priority.  If this is the first file or the first history file
         * ever, copy it.  In the presence of a history file already chosen as
         * target, ignore all other files except history files which have been
         * generated for an older timeline than what is already chosen as
         * target to archive.
         */
        if (!found || (ishistory && !historyFound))
        {
            strcpy(xlog, basename);
            found = true;
            historyFound = ishistory;
        }
        else if (ishistory || !historyFound)
        {
            if (strcmp(basename, xlog) < 0)
                strcpy(xlog, basename);
        }
    }
    FreeDir(rldir);

    return found;
}

/*
 * pgarch_archiveDone
 *
 * Emit notification that an xlog file has been successfully archived.
 * We do this by renaming the status file from NNN.ready to NNN.done.
 * Eventually, a checkpoint process will notice this and delete both the
 * NNN.done file and the xlog file itself.
 */
static void
pgarch_archiveDone(char *xlog)
{
    char        rlogready[MAXPGPATH];
    char        rlogdone[MAXPGPATH];

    StatusFilePath(rlogready, xlog, ".ready");
    StatusFilePath(rlogdone, xlog, ".done");
    (void) durable_rename(rlogready, rlogdone, WARNING);
}