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316 lines
8.8 KiB
C
316 lines
8.8 KiB
C
/*-------------------------------------------------------------------------
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*
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* walwriter.c
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*
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* The WAL writer background process is new as of Postgres 8.3. It attempts
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* to keep regular backends from having to write out (and fsync) WAL pages.
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* Also, it guarantees that transaction commit records that weren't synced
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* to disk immediately upon commit (ie, were "asynchronously committed")
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* will reach disk within a knowable time --- which, as it happens, is at
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* most three times the wal_writer_delay cycle time.
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*
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* Note that as with the bgwriter for shared buffers, regular backends are
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* still empowered to issue WAL writes and fsyncs when the walwriter doesn't
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* keep up.
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*
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* Because the walwriter's cycle is directly linked to the maximum delay
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* before async-commit transactions are guaranteed committed, it's probably
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* unwise to load additional functionality onto it. For instance, if you've
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* got a yen to create xlog segments further in advance, that'd be better done
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* in bgwriter than in walwriter.
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*
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* The walwriter is started by the postmaster as soon as the startup subprocess
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* finishes. It remains alive until the postmaster commands it to terminate.
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* Normal termination is by SIGTERM, which instructs the walwriter to exit(0).
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* Emergency termination is by SIGQUIT; like any backend, the walwriter will
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* simply abort and exit on SIGQUIT.
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*
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* If the walwriter exits unexpectedly, the postmaster treats that the same
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* as a backend crash: shared memory may be corrupted, so remaining backends
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* should be killed by SIGQUIT and then a recovery cycle started.
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*
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*
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* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/postmaster/walwriter.c,v 1.4 2008/01/01 19:45:51 momjian Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include <signal.h>
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#include <sys/time.h>
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#include <time.h>
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#include <unistd.h>
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#include "access/xlog.h"
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#include "libpq/pqsignal.h"
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#include "miscadmin.h"
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#include "postmaster/walwriter.h"
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#include "storage/bufmgr.h"
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#include "storage/fd.h"
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#include "storage/ipc.h"
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#include "storage/lwlock.h"
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#include "storage/pmsignal.h"
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#include "storage/smgr.h"
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#include "utils/guc.h"
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#include "utils/hsearch.h"
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#include "utils/memutils.h"
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#include "utils/resowner.h"
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/*
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* GUC parameters
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*/
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int WalWriterDelay = 200;
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/*
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* Flags set by interrupt handlers for later service in the main loop.
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*/
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static volatile sig_atomic_t got_SIGHUP = false;
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static volatile sig_atomic_t shutdown_requested = false;
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/* Signal handlers */
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static void wal_quickdie(SIGNAL_ARGS);
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static void WalSigHupHandler(SIGNAL_ARGS);
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static void WalShutdownHandler(SIGNAL_ARGS);
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/*
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* Main entry point for walwriter process
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*
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* This is invoked from BootstrapMain, which has already created the basic
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* execution environment, but not enabled signals yet.
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*/
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void
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WalWriterMain(void)
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{
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sigjmp_buf local_sigjmp_buf;
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MemoryContext walwriter_context;
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/*
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* If possible, make this process a group leader, so that the postmaster
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* can signal any child processes too. (walwriter probably never has any
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* child processes, but for consistency we make all postmaster child
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* processes do this.)
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*/
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#ifdef HAVE_SETSID
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if (setsid() < 0)
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elog(FATAL, "setsid() failed: %m");
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#endif
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/*
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* Properly accept or ignore signals the postmaster might send us
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*
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* We have no particular use for SIGINT at the moment, but seems
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* reasonable to treat like SIGTERM.
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*/
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pqsignal(SIGHUP, WalSigHupHandler); /* set flag to read config file */
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pqsignal(SIGINT, WalShutdownHandler); /* request shutdown */
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pqsignal(SIGTERM, WalShutdownHandler); /* request shutdown */
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pqsignal(SIGQUIT, wal_quickdie); /* hard crash time */
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pqsignal(SIGALRM, SIG_IGN);
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pqsignal(SIGPIPE, SIG_IGN);
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pqsignal(SIGUSR1, SIG_IGN); /* reserve for sinval */
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pqsignal(SIGUSR2, SIG_IGN); /* not used */
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/*
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* Reset some signals that are accepted by postmaster but not here
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*/
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pqsignal(SIGCHLD, SIG_DFL);
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pqsignal(SIGTTIN, SIG_DFL);
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pqsignal(SIGTTOU, SIG_DFL);
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pqsignal(SIGCONT, SIG_DFL);
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pqsignal(SIGWINCH, SIG_DFL);
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/* We allow SIGQUIT (quickdie) at all times */
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#ifdef HAVE_SIGPROCMASK
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sigdelset(&BlockSig, SIGQUIT);
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#else
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BlockSig &= ~(sigmask(SIGQUIT));
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#endif
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/*
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* Create a resource owner to keep track of our resources (not clear that
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* we need this, but may as well have one).
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*/
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CurrentResourceOwner = ResourceOwnerCreate(NULL, "Wal Writer");
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/*
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* Create a memory context that we will do all our work in. We do this so
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* that we can reset the context during error recovery and thereby avoid
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* possible memory leaks. Formerly this code just ran in
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* TopMemoryContext, but resetting that would be a really bad idea.
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*/
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walwriter_context = AllocSetContextCreate(TopMemoryContext,
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"Wal Writer",
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ALLOCSET_DEFAULT_MINSIZE,
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ALLOCSET_DEFAULT_INITSIZE,
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ALLOCSET_DEFAULT_MAXSIZE);
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MemoryContextSwitchTo(walwriter_context);
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/*
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* If an exception is encountered, processing resumes here.
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*
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* This code is heavily based on bgwriter.c, q.v.
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*/
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if (sigsetjmp(local_sigjmp_buf, 1) != 0)
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{
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/* Since not using PG_TRY, must reset error stack by hand */
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error_context_stack = NULL;
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/* Prevent interrupts while cleaning up */
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HOLD_INTERRUPTS();
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/* Report the error to the server log */
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EmitErrorReport();
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/*
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* These operations are really just a minimal subset of
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* AbortTransaction(). We don't have very many resources to worry
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* about in walwriter, but we do have LWLocks, and perhaps buffers?
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*/
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LWLockReleaseAll();
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AbortBufferIO();
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UnlockBuffers();
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/* buffer pins are released here: */
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ResourceOwnerRelease(CurrentResourceOwner,
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RESOURCE_RELEASE_BEFORE_LOCKS,
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false, true);
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/* we needn't bother with the other ResourceOwnerRelease phases */
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AtEOXact_Buffers(false);
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AtEOXact_Files();
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AtEOXact_HashTables(false);
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/*
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* Now return to normal top-level context and clear ErrorContext for
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* next time.
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*/
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MemoryContextSwitchTo(walwriter_context);
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FlushErrorState();
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/* Flush any leaked data in the top-level context */
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MemoryContextResetAndDeleteChildren(walwriter_context);
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/* Now we can allow interrupts again */
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RESUME_INTERRUPTS();
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/*
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* Sleep at least 1 second after any error. A write error is likely
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* to be repeated, and we don't want to be filling the error logs as
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* fast as we can.
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*/
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pg_usleep(1000000L);
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/*
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* Close all open files after any error. This is helpful on Windows,
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* where holding deleted files open causes various strange errors.
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* It's not clear we need it elsewhere, but shouldn't hurt.
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*/
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smgrcloseall();
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}
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/* We can now handle ereport(ERROR) */
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PG_exception_stack = &local_sigjmp_buf;
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/*
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* Unblock signals (they were blocked when the postmaster forked us)
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*/
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PG_SETMASK(&UnBlockSig);
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/*
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* Loop forever
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*/
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for (;;)
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{
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long udelay;
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/*
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* Emergency bailout if postmaster has died. This is to avoid the
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* necessity for manual cleanup of all postmaster children.
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*/
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if (!PostmasterIsAlive(true))
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exit(1);
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/*
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* Process any requests or signals received recently.
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*/
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if (got_SIGHUP)
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{
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got_SIGHUP = false;
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ProcessConfigFile(PGC_SIGHUP);
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}
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if (shutdown_requested)
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{
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/* Normal exit from the walwriter is here */
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proc_exit(0); /* done */
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}
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/*
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* Do what we're here for...
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*/
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XLogBackgroundFlush();
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/*
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* Delay until time to do something more, but fall out of delay
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* reasonably quickly if signaled.
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*/
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udelay = WalWriterDelay * 1000L;
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while (udelay > 999999L)
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{
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if (got_SIGHUP || shutdown_requested)
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break;
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pg_usleep(1000000L);
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udelay -= 1000000L;
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}
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if (!(got_SIGHUP || shutdown_requested))
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pg_usleep(udelay);
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}
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}
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/* --------------------------------
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* signal handler routines
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* --------------------------------
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*/
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/*
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* wal_quickdie() occurs when signalled SIGQUIT by the postmaster.
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*
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* Some backend has bought the farm,
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* so we need to stop what we're doing and exit.
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*/
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static void
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wal_quickdie(SIGNAL_ARGS)
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{
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PG_SETMASK(&BlockSig);
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/*
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* DO NOT proc_exit() -- we're here because shared memory may be
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* corrupted, so we don't want to try to clean up our transaction. Just
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* nail the windows shut and get out of town.
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*
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* Note we do exit(2) not exit(0). This is to force the postmaster into a
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* system reset cycle if some idiot DBA sends a manual SIGQUIT to a random
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* backend. This is necessary precisely because we don't clean up our
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* shared memory state.
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*/
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exit(2);
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}
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/* SIGHUP: set flag to re-read config file at next convenient time */
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static void
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WalSigHupHandler(SIGNAL_ARGS)
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{
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got_SIGHUP = true;
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}
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/* SIGTERM: set flag to exit normally */
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static void
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WalShutdownHandler(SIGNAL_ARGS)
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{
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shutdown_requested = true;
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}
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