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walwriter.c File Reference

#include "postgres.h"
#include <signal.h>
#include <sys/time.h>
#include <unistd.h>
#include "access/xlog.h"
#include "libpq/pqsignal.h"
#include "miscadmin.h"
#include "postmaster/walwriter.h"
#include "storage/bufmgr.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/lwlock.h"
#include "storage/proc.h"
#include "storage/smgr.h"
#include "utils/guc.h"
#include "utils/hsearch.h"
#include "utils/memutils.h"
#include "utils/resowner.h"
Include dependency graph for walwriter.c:

Go to the source code of this file.




static void wal_quickdie (SIGNAL_ARGS)
static void WalSigHupHandler (SIGNAL_ARGS)
static void WalShutdownHandler (SIGNAL_ARGS)
static void walwriter_sigusr1_handler (SIGNAL_ARGS)
void WalWriterMain (void)


int WalWriterDelay = 200
static volatile sig_atomic_t got_SIGHUP = false
static volatile sig_atomic_t shutdown_requested = false

Define Documentation


Definition at line 76 of file walwriter.c.


Definition at line 75 of file walwriter.c.

Function Documentation

static void wal_quickdie ( SIGNAL_ARGS   )  [static]

Definition at line 329 of file walwriter.c.

References BlockSig, on_exit_reset(), and PG_SETMASK.

Referenced by WalWriterMain().


     * We DO NOT want to run proc_exit() callbacks -- we're here because
     * shared memory may be corrupted, so we don't want to try to clean up our
     * transaction.  Just nail the windows shut and get out of town.  Now that
     * there's an atexit callback to prevent third-party code from breaking
     * things by calling exit() directly, we have to reset the callbacks
     * explicitly to make this work as intended.

     * Note we do exit(2) not exit(0).  This is to force the postmaster into a
     * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random
     * backend.  This is necessary precisely because we don't clean up our
     * shared memory state.  (The "dead man switch" mechanism in pmsignal.c
     * should ensure the postmaster sees this as a crash, too, but no harm in
     * being doubly sure.)

static void WalShutdownHandler ( SIGNAL_ARGS   )  [static]

Definition at line 369 of file walwriter.c.

References MyProc, PGPROC::procLatch, SetLatch(), and shutdown_requested.

Referenced by WalWriterMain().

    int         save_errno = errno;

    shutdown_requested = true;
    if (MyProc)

    errno = save_errno;

static void WalSigHupHandler ( SIGNAL_ARGS   )  [static]

Definition at line 356 of file walwriter.c.

References got_SIGHUP, MyProc, PGPROC::procLatch, and SetLatch().

Referenced by WalWriterMain().

    int         save_errno = errno;

    got_SIGHUP = true;
    if (MyProc)

    errno = save_errno;

static void walwriter_sigusr1_handler ( SIGNAL_ARGS   )  [static]

Definition at line 382 of file walwriter.c.

References latch_sigusr1_handler().

Referenced by WalWriterMain().

    int         save_errno = errno;


    errno = save_errno;

void WalWriterMain ( void   ) 

Definition at line 97 of file walwriter.c.

References AbortBufferIO(), ALLOCSET_DEFAULT_INITSIZE, ALLOCSET_DEFAULT_MAXSIZE, ALLOCSET_DEFAULT_MINSIZE, AllocSetContextCreate(), AtEOXact_Buffers(), AtEOXact_Files(), AtEOXact_HashTables(), AtEOXact_SMgr(), BlockSig, CurrentResourceOwner, elog, EmitErrorReport(), error_context_stack, FATAL, FlushErrorState(), got_SIGHUP, HOLD_INTERRUPTS, LWLockReleaseAll(), MemoryContextResetAndDeleteChildren(), MemoryContextSwitchTo(), MyProc, NULL, PG_exception_stack, PG_SETMASK, pg_usleep(), PGC_SIGHUP, pqsignal(), proc_exit(), ProcessConfigFile(), ProcGlobal, PGPROC::procLatch, ResetLatch(), RESOURCE_RELEASE_BEFORE_LOCKS, ResourceOwnerCreate(), ResourceOwnerRelease(), RESUME_INTERRUPTS, SetWalWriterSleeping(), shutdown_requested, SIG_DFL, SIG_IGN, SIGALRM, SIGCHLD, SIGCONT, sigdelset, SIGHUP, sigjmp_buf, SIGPIPE, SIGQUIT, sigsetjmp, SIGTTIN, SIGTTOU, SIGUSR1, SIGUSR2, SIGWINCH, smgrcloseall(), TopMemoryContext, UnBlockSig, UnlockBuffers(), WaitLatch(), wal_quickdie(), WalShutdownHandler(), WalSigHupHandler(), walwriter_sigusr1_handler(), WalWriterDelay, PROC_HDR::walwriterLatch, WL_LATCH_SET, WL_POSTMASTER_DEATH, WL_TIMEOUT, and XLogBackgroundFlush().

Referenced by AuxiliaryProcessMain().

    sigjmp_buf  local_sigjmp_buf;
    MemoryContext walwriter_context;
    int         left_till_hibernate;
    bool        hibernating;

     * If possible, make this process a group leader, so that the postmaster
     * can signal any child processes too.  (walwriter probably never has any
     * child processes, but for consistency we make all postmaster child
     * processes do this.)
    if (setsid() < 0)
        elog(FATAL, "setsid() failed: %m");

     * Properly accept or ignore signals the postmaster might send us
     * We have no particular use for SIGINT at the moment, but seems
     * reasonable to treat like SIGTERM.
    pqsignal(SIGHUP, WalSigHupHandler); /* set flag to read config file */
    pqsignal(SIGINT, WalShutdownHandler);       /* request shutdown */
    pqsignal(SIGTERM, WalShutdownHandler);      /* request shutdown */
    pqsignal(SIGQUIT, wal_quickdie);    /* hard crash time */
    pqsignal(SIGALRM, SIG_IGN);
    pqsignal(SIGPIPE, SIG_IGN);
    pqsignal(SIGUSR1, walwriter_sigusr1_handler);
    pqsignal(SIGUSR2, SIG_IGN); /* not used */

     * Reset some signals that are accepted by postmaster but not here
    pqsignal(SIGCHLD, SIG_DFL);
    pqsignal(SIGTTIN, SIG_DFL);
    pqsignal(SIGTTOU, SIG_DFL);
    pqsignal(SIGCONT, SIG_DFL);
    pqsignal(SIGWINCH, SIG_DFL);

    /* We allow SIGQUIT (quickdie) at all times */
    sigdelset(&BlockSig, SIGQUIT);

     * Create a resource owner to keep track of our resources (not clear that
     * we need this, but may as well have one).
    CurrentResourceOwner = ResourceOwnerCreate(NULL, "Wal Writer");

     * Create a memory context that we will do all our work in.  We do this so
     * that we can reset the context during error recovery and thereby avoid
     * possible memory leaks.  Formerly this code just ran in
     * TopMemoryContext, but resetting that would be a really bad idea.
    walwriter_context = AllocSetContextCreate(TopMemoryContext,
                                              "Wal Writer",

     * If an exception is encountered, processing resumes here.
     * This code is heavily based on bgwriter.c, q.v.
    if (sigsetjmp(local_sigjmp_buf, 1) != 0)
        /* Since not using PG_TRY, must reset error stack by hand */
        error_context_stack = NULL;

        /* Prevent interrupts while cleaning up */

        /* Report the error to the server log */

         * These operations are really just a minimal subset of
         * AbortTransaction().  We don't have very many resources to worry
         * about in walwriter, but we do have LWLocks, and perhaps buffers?
        /* buffer pins are released here: */
                             false, true);
        /* we needn't bother with the other ResourceOwnerRelease phases */

         * Now return to normal top-level context and clear ErrorContext for
         * next time.

        /* Flush any leaked data in the top-level context */

        /* Now we can allow interrupts again */

         * Sleep at least 1 second after any error.  A write error is likely
         * to be repeated, and we don't want to be filling the error logs as
         * fast as we can.

         * Close all open files after any error.  This is helpful on Windows,
         * where holding deleted files open causes various strange errors.
         * It's not clear we need it elsewhere, but shouldn't hurt.

    /* We can now handle ereport(ERROR) */
    PG_exception_stack = &local_sigjmp_buf;

     * Unblock signals (they were blocked when the postmaster forked us)

     * Reset hibernation state after any error.
    left_till_hibernate = LOOPS_UNTIL_HIBERNATE;
    hibernating = false;

     * Advertise our latch that backends can use to wake us up while we're
     * sleeping.
    ProcGlobal->walwriterLatch = &MyProc->procLatch;

     * Loop forever
    for (;;)
        long        cur_timeout;
        int         rc;

         * Advertise whether we might hibernate in this cycle.  We do this
         * before resetting the latch to ensure that any async commits will
         * see the flag set if they might possibly need to wake us up, and
         * that we won't miss any signal they send us.  (If we discover work
         * to do in the last cycle before we would hibernate, the global flag
         * will be set unnecessarily, but little harm is done.)  But avoid
         * touching the global flag if it doesn't need to change.
        if (hibernating != (left_till_hibernate <= 1))
            hibernating = (left_till_hibernate <= 1);

        /* Clear any already-pending wakeups */

         * Process any requests or signals received recently.
        if (got_SIGHUP)
            got_SIGHUP = false;
        if (shutdown_requested)
            /* Normal exit from the walwriter is here */
            proc_exit(0);       /* done */

         * Do what we're here for; then, if XLogBackgroundFlush() found useful
         * work to do, reset hibernation counter.
        if (XLogBackgroundFlush())
            left_till_hibernate = LOOPS_UNTIL_HIBERNATE;
        else if (left_till_hibernate > 0)

         * Sleep until we are signaled or WalWriterDelay has elapsed.  If we
         * haven't done anything useful for quite some time, lengthen the
         * sleep time so as to reduce the server's idle power consumption.
        if (left_till_hibernate > 0)
            cur_timeout = WalWriterDelay;       /* in ms */
            cur_timeout = WalWriterDelay * HIBERNATE_FACTOR;

        rc = WaitLatch(&MyProc->procLatch,

         * Emergency bailout if postmaster has died.  This is to avoid the
         * necessity for manual cleanup of all postmaster children.
        if (rc & WL_POSTMASTER_DEATH)

Variable Documentation

volatile sig_atomic_t got_SIGHUP = false [static]

Definition at line 81 of file walwriter.c.

Referenced by WalSigHupHandler(), and WalWriterMain().

volatile sig_atomic_t shutdown_requested = false [static]

Definition at line 82 of file walwriter.c.

Referenced by WalShutdownHandler(), and WalWriterMain().

int WalWriterDelay = 200

Definition at line 68 of file walwriter.c.

Referenced by WalWriterMain().