| /*------------------------------------------------------------------------- |
| * |
| * bgwriter.c |
| * |
| * The background writer (bgwriter) is new as of Postgres 8.0. It attempts |
| * to keep regular backends from having to write out dirty shared buffers |
| * (which they would only do when needing to free a shared buffer to read in |
| * another page). In the best scenario all writes from shared buffers will |
| * be issued by the background writer process. However, regular backends are |
| * still empowered to issue writes if the bgwriter fails to maintain enough |
| * clean shared buffers. |
| * |
| * Previously, the background writer use to do this duty. But we ended up with |
| * a deadlock with the new FileRep functionality, so this functionality was split out into its |
| * own server. |
| * |
| * The bgwriter is started by the postmaster as soon as the startup subprocess |
| * finishes. It remains alive until the postmaster commands it to terminate. |
| * Normal termination is by SIGUSR2, which instructs the bgwriter to execute |
| * a shutdown checkpoint and then exit(0). (All backends must be stopped |
| * before SIGUSR2 is issued!) Emergency termination is by SIGQUIT; like any |
| * backend, the bgwriter will simply abort and exit on SIGQUIT. |
| * |
| * If the bgwriter exits unexpectedly, the postmaster treats that the same |
| * as a backend crash: shared memory may be corrupted, so remaining backends |
| * should be killed by SIGQUIT and then a recovery cycle started. (Even if |
| * shared memory isn't corrupted, we have lost information about which |
| * files need to be fsync'd for the next checkpoint, and so a system |
| * restart needs to be forced.) |
| * |
| * |
| * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group |
| * |
| * |
| * IDENTIFICATION |
| * $PostgreSQL: pgsql/src/backend/postmaster/bgwriter.c,v 1.33.2.2 2007/09/11 17:15:40 tgl Exp $ |
| * |
| *------------------------------------------------------------------------- |
| */ |
| #include "postgres.h" |
| |
| #include <signal.h> |
| #include <time.h> |
| #include <unistd.h> |
| |
| #include "access/xlog_internal.h" |
| #include "libpq/pqsignal.h" |
| #include "miscadmin.h" |
| #include "postmaster/bgwriter.h" |
| #include "storage/fd.h" |
| #include "storage/freespace.h" |
| #include "storage/ipc.h" |
| #include "storage/lwlock.h" |
| #include "storage/pmsignal.h" |
| #include "storage/shmem.h" |
| #include "storage/smgr.h" |
| #include "tcop/tcopprot.h" |
| #include "utils/guc.h" |
| #include "utils/memutils.h" |
| #include "utils/resowner.h" |
| #include "utils/faultinjector.h" |
| |
| #include "tcop/tcopprot.h" /* quickdie() */ |
| |
| /*---------- |
| * Shared memory area for communication between bgwriter and backends |
| * |
| * The requests array holds fsync requests sent by backends and not yet |
| * absorbed by the bgwriter. Unlike the checkpoint fields, the requests |
| * fields are protected by BgWriterCommLock. |
| *---------- |
| */ |
| typedef struct |
| { |
| RelFileNode rnode; |
| BlockNumber segno; /* see md.c for special values */ |
| /* might add a real request-type field later; not needed yet */ |
| } BgWriterRequest; |
| |
| typedef struct |
| { |
| pid_t bgwriter_pid; /* PID of bgwriter (0 if not started) */ |
| |
| int num_requests; /* current # of requests */ |
| int max_requests; /* allocated array size */ |
| BgWriterRequest requests[1]; /* VARIABLE LENGTH ARRAY */ |
| } BgWriterShmemStruct; |
| |
| static BgWriterShmemStruct *BgWriterShmem; |
| |
| /* |
| * GUC parameters |
| */ |
| int BgWriterDelay = 200; |
| |
| /* |
| * Flags set by interrupt handlers for later service in the main loop. |
| */ |
| static volatile sig_atomic_t got_SIGHUP = false; |
| static volatile sig_atomic_t checkpoint_smgrcloseall_requested = false; |
| static volatile sig_atomic_t shutdown_requested = false; |
| |
| /* |
| * Private state |
| */ |
| static bool am_bg_writer = false; |
| |
| static time_t last_xlog_switch_time; |
| |
| static void BgSigHupHandler(SIGNAL_ARGS); |
| static void ReqCheckpointSmgrCloseHandler(SIGNAL_ARGS); |
| static void ReqShutdownHandler(SIGNAL_ARGS); |
| |
| /* |
| * Main entry point for bgwriter process |
| * |
| * This is invoked from AuxiliaryProcessMain, which has already created the basic |
| * execution environment, but not enabled signals yet. |
| */ |
| void |
| BackgroundWriterMain(void) |
| { |
| sigjmp_buf local_sigjmp_buf; |
| MemoryContext bgwriter_context; |
| |
| Assert(BgWriterShmem != NULL); |
| BgWriterShmem->bgwriter_pid = MyProcPid; |
| am_bg_writer = true; |
| |
| /* |
| * If possible, make this process a group leader, so that the postmaster |
| * can signal any child processes too. (bgwriter probably never has |
| * any child processes, but for consistency we make all postmaster |
| * child processes do this.) |
| */ |
| #ifdef HAVE_SETSID |
| if (setsid() < 0) |
| elog(FATAL, "setsid() failed: %m"); |
| #endif |
| |
| /* |
| * Properly accept or ignore signals the postmaster might send us |
| * |
| * Note: we deliberately ignore SIGTERM, because during a standard Unix |
| * system shutdown cycle, init will SIGTERM all processes at once. We |
| * want to wait for the backends to exit, whereupon the postmaster will |
| * tell us it's okay to shut down (via SIGUSR2). |
| * |
| * SIGUSR1 is presently unused; keep it spare in case someday we want this |
| * process to participate in ProcSignal messaging. |
| */ |
| pqsignal(SIGHUP, BgSigHupHandler); /* set flag to read config file */ |
| pqsignal(SIGINT, ReqCheckpointSmgrCloseHandler); /* request checkpoint smgrcloseall */ |
| pqsignal(SIGTERM, SIG_IGN); /* ignore SIGTERM */ |
| pqsignal(SIGQUIT, quickdie); /* hard crash time: nothing bg-writer specific, just use the standard */ |
| pqsignal(SIGALRM, SIG_IGN); |
| pqsignal(SIGPIPE, SIG_IGN); |
| pqsignal(SIGUSR1, SIG_IGN); /* reserve for ProcSignal */ |
| pqsignal(SIGUSR2, ReqShutdownHandler); /* request shutdown */ |
| |
| /* |
| * 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 */ |
| #ifdef HAVE_SIGPROCMASK |
| sigdelset(&BlockSig, SIGQUIT); |
| #else |
| BlockSig &= ~(sigmask(SIGQUIT)); |
| #endif |
| |
| /* |
| * Initialize so that first time-driven event happens at the correct time. |
| */ |
| last_xlog_switch_time = time(NULL); |
| |
| /* |
| * Create a resource owner to keep track of our resources (currently only |
| * buffer pins). |
| */ |
| CurrentResourceOwner = ResourceOwnerCreate(NULL, "Background 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. |
| */ |
| bgwriter_context = AllocSetContextCreate(TopMemoryContext, |
| "Background Writer", |
| ALLOCSET_DEFAULT_MINSIZE, |
| ALLOCSET_DEFAULT_INITSIZE, |
| ALLOCSET_DEFAULT_MAXSIZE); |
| MemoryContextSwitchTo(bgwriter_context); |
| |
| /* |
| * If an exception is encountered, processing resumes here. |
| * |
| * See notes in postgres.c about the design of this coding. |
| */ |
| 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 */ |
| HOLD_INTERRUPTS(); |
| |
| /* Report the error to the server log */ |
| EmitErrorReport(); |
| |
| /* |
| * These operations are really just a minimal subset of |
| * AbortTransaction(). We don't have very many resources to worry |
| * about in bgwriter, but we do have LWLocks, buffers, and temp files. |
| */ |
| LWLockReleaseAll(); |
| AbortBufferIO(); |
| UnlockBuffers(); |
| /* buffer pins are released here: */ |
| ResourceOwnerRelease(CurrentResourceOwner, |
| RESOURCE_RELEASE_BEFORE_LOCKS, |
| false, true); |
| /* we needn't bother with the other ResourceOwnerRelease phases */ |
| AtEOXact_Buffers(false); |
| AtEOXact_Files(); |
| AtEOXact_HashTables(false); |
| |
| /* |
| * Now return to normal top-level context and clear ErrorContext for |
| * next time. |
| */ |
| MemoryContextSwitchTo(bgwriter_context); |
| FlushErrorState(); |
| |
| /* Flush any leaked data in the top-level context */ |
| MemoryContextResetAndDeleteChildren(bgwriter_context); |
| |
| /* Now we can allow interrupts again */ |
| RESUME_INTERRUPTS(); |
| |
| /* |
| * 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. |
| */ |
| pg_usleep(1000000L); |
| |
| /* |
| * 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. |
| */ |
| smgrcloseall(); |
| } |
| |
| /* We can now handle ereport(ERROR) */ |
| PG_exception_stack = &local_sigjmp_buf; |
| |
| /* |
| * Unblock signals (they were blocked when the postmaster forked us) |
| */ |
| PG_SETMASK(&UnBlockSig); |
| |
| /* |
| * Loop forever |
| */ |
| for (;;) |
| { |
| bool do_checkpoint_smgrcloseall = false; |
| time_t now = time(NULL); |
| long udelay; |
| |
| /* |
| * Emergency bailout if postmaster has died. This is to avoid the |
| * necessity for manual cleanup of all postmaster children. |
| */ |
| if (!PostmasterIsAlive(true)) |
| exit(1); |
| |
| #ifdef USE_ASSERT_CHECKING |
| #ifdef FAULT_INJECTOR |
| FaultInjector_InjectFaultIfSet( |
| FaultInBackgroundWriterMain, |
| DDLNotSpecified, |
| "", // databaseName |
| ""); // tableName |
| #endif |
| #endif |
| /* |
| * Process any requests or signals received recently. |
| */ |
| AbsorbFsyncRequests(); |
| |
| if (got_SIGHUP) |
| { |
| got_SIGHUP = false; |
| ProcessConfigFile(PGC_SIGHUP); |
| } |
| if (checkpoint_smgrcloseall_requested) |
| { |
| checkpoint_smgrcloseall_requested = false; |
| do_checkpoint_smgrcloseall = true; |
| } |
| if (shutdown_requested) |
| { |
| /* |
| * From here on, elog(ERROR) should end with exit(1), not send |
| * control back to the sigsetjmp block above |
| */ |
| ExitOnAnyError = true; |
| /* Close down the database */ |
| ShutdownXLOG(0, 0); |
| DumpFreeSpaceMap(0, 0); |
| |
| /* Normal exit from the bgwriter server is here */ |
| if (Debug_print_server_processes || |
| Debug_print_qd_mirroring || |
| log_min_messages <= DEBUG5) |
| { |
| ereport((log_min_messages > DEBUG5 ? LOG : DEBUG5), |
| (errmsg("normal exit from background writer"))); |
| } |
| proc_exit(0); /* done */ |
| } |
| |
| /* |
| * Do a checkpoint smgrcloseall if requested, otherwise do one cycle of |
| * dirty-buffer writing. |
| */ |
| if (do_checkpoint_smgrcloseall) |
| { |
| /* |
| * After any checkpoint, close all smgr files. This is so we |
| * won't hang onto smgr references to deleted files indefinitely. |
| */ |
| smgrcloseall(); |
| } |
| else |
| BgBufferSync(); |
| |
| /* |
| * Check for archive_timeout, if so, switch xlog files. First we do a |
| * quick check using possibly-stale local state. |
| */ |
| if (XLogArchiveTimeout > 0 && |
| (int) (now - last_xlog_switch_time) >= XLogArchiveTimeout) |
| { |
| /* |
| * Update local state ... note that last_xlog_switch_time is the |
| * last time a switch was performed *or requested*. |
| */ |
| time_t last_time = GetLastSegSwitchTime(); |
| |
| last_xlog_switch_time = Max(last_xlog_switch_time, last_time); |
| |
| /* if we did a checkpoint, 'now' might be stale too */ |
| if (do_checkpoint_smgrcloseall) |
| now = time(NULL); |
| |
| /* Now we can do the real check */ |
| if ((int) (now - last_xlog_switch_time) >= XLogArchiveTimeout) |
| { |
| XLogRecPtr switchpoint; |
| |
| /* OK, it's time to switch */ |
| switchpoint = RequestXLogSwitch(); |
| |
| /* |
| * If the returned pointer points exactly to a segment |
| * boundary, assume nothing happened. |
| */ |
| if ((switchpoint.xrecoff % XLogSegSize) != 0) |
| ereport(DEBUG1, |
| (errmsg("transaction log switch forced (archive_timeout=%d)", |
| XLogArchiveTimeout))); |
| |
| /* |
| * Update state in any case, so we don't retry constantly when |
| * the system is idle. |
| */ |
| last_xlog_switch_time = now; |
| } |
| } |
| |
| /* |
| * Nap for the configured time, or sleep for 10 seconds if there is no |
| * bgwriter activity configured. |
| * |
| * On some platforms, signals won't interrupt the sleep. To ensure we |
| * respond reasonably promptly when someone signals us, break down the |
| * sleep into 1-second increments, and check for interrupts after each |
| * nap. |
| * |
| * We absorb pending requests after each short sleep. |
| */ |
| if ((bgwriter_all_percent > 0.0 && bgwriter_all_maxpages > 0) || |
| (bgwriter_lru_percent > 0.0 && bgwriter_lru_maxpages > 0)) |
| udelay = BgWriterDelay * 1000L; |
| else if (XLogArchiveTimeout > 0) |
| udelay = 1000000L; /* One second */ |
| else |
| udelay = 10000000L; /* Ten seconds */ |
| |
| while (udelay > 999999L) |
| { |
| if (got_SIGHUP || checkpoint_smgrcloseall_requested || shutdown_requested) |
| break; |
| pg_usleep(1000000L); |
| AbsorbFsyncRequests(); |
| udelay -= 1000000L; |
| } |
| |
| if (!(got_SIGHUP || checkpoint_smgrcloseall_requested || shutdown_requested)) |
| pg_usleep(udelay); |
| } |
| } |
| |
| |
| /* -------------------------------- |
| * signal handler routines |
| * -------------------------------- |
| */ |
| |
| /* SIGHUP: set flag to re-read config file at next convenient time */ |
| static void |
| BgSigHupHandler(SIGNAL_ARGS) |
| { |
| got_SIGHUP = true; |
| } |
| |
| /* SIGINT: set flag to run a normal checkpoint right away */ |
| static void |
| ReqCheckpointSmgrCloseHandler(SIGNAL_ARGS) |
| { |
| checkpoint_smgrcloseall_requested = true; |
| } |
| |
| /* SIGUSR2: set flag to run a shutdown checkpoint and exit */ |
| static void |
| ReqShutdownHandler(SIGNAL_ARGS) |
| { |
| shutdown_requested = true; |
| } |
| |
| |
| /* -------------------------------- |
| * communication with backends |
| * -------------------------------- |
| */ |
| |
| /* |
| * BgWriterShmemSize |
| * Compute space needed for bgwriter-related shared memory |
| */ |
| Size |
| BgWriterShmemSize(void) |
| { |
| Size size; |
| |
| /* |
| * Currently, the size of the requests[] array is arbitrarily set equal to |
| * NBuffers. This may prove too large or small ... |
| */ |
| size = offsetof(BgWriterShmemStruct, requests); |
| size = add_size(size, mul_size(NBuffers, sizeof(BgWriterRequest))); |
| |
| return size; |
| } |
| |
| /* |
| * BgWriterShmemInit |
| * Allocate and initialize bgwriter-related shared memory |
| */ |
| void |
| BgWriterShmemInit(void) |
| { |
| bool found; |
| |
| BgWriterShmem = (BgWriterShmemStruct *) |
| ShmemInitStruct("Background Writer Data", |
| BgWriterShmemSize(), |
| &found); |
| if (BgWriterShmem == NULL) |
| ereport(FATAL, |
| (errcode(ERRCODE_OUT_OF_MEMORY), |
| errmsg("not enough shared memory for background writer"))); |
| if (found) |
| return; /* already initialized */ |
| |
| MemSet(BgWriterShmem, 0, sizeof(BgWriterShmemStruct)); |
| BgWriterShmem->max_requests = NBuffers; |
| } |
| |
| /* |
| * RequestCheckpointSmgrCloseAll |
| * Called in checkpoint server process to request the background writer do a smgrcloseall. |
| */ |
| void |
| RequestCheckpointSmgrCloseAll(void) |
| { |
| /* |
| * Send signal to request checkpoint. When waitforit is false, we |
| * consider failure to send the signal to be nonfatal. |
| */ |
| if (BgWriterShmem->bgwriter_pid == 0) |
| elog(LOG, |
| "could not request checkpoint close all because bgwriter not running"); |
| if (kill(BgWriterShmem->bgwriter_pid, SIGINT) != 0) |
| elog(LOG, |
| "could not signal bgwriter for checkpoint close all: %m"); |
| } |
| |
| /* |
| * ForwardFsyncRequest |
| * Forward a file-fsync request from a backend to the bgwriter |
| * |
| * Whenever a backend is compelled to write directly to a relation |
| * (which should be seldom, if the bgwriter is getting its job done), |
| * the backend calls this routine to pass over knowledge that the relation |
| * is dirty and must be fsync'd before next checkpoint. |
| * |
| * segno specifies which segment (not block!) of the relation needs to be |
| * fsync'd. (Since the valid range is much less than BlockNumber, we can |
| * use high values for special flags; that's all internal to md.c, which |
| * see for details.) |
| * |
| * If we are unable to pass over the request (at present, this can happen |
| * if the shared memory queue is full), we return false. That forces |
| * the backend to do its own fsync. We hope that will be even more seldom. |
| * |
| * Note: we presently make no attempt to eliminate duplicate requests |
| * in the requests[] queue. The bgwriter will have to eliminate dups |
| * internally anyway, so we may as well avoid holding the lock longer |
| * than we have to here. |
| */ |
| bool |
| ForwardFsyncRequest(RelFileNode rnode, BlockNumber segno) |
| { |
| BgWriterRequest *request; |
| |
| if (!IsUnderPostmaster) |
| return false; /* probably shouldn't even get here */ |
| Assert(BgWriterShmem != NULL); |
| |
| LWLockAcquire(BgWriterCommLock, LW_EXCLUSIVE); |
| if (BgWriterShmem->bgwriter_pid == 0 || |
| BgWriterShmem->num_requests >= BgWriterShmem->max_requests) |
| { |
| LWLockRelease(BgWriterCommLock); |
| return false; |
| } |
| request = &BgWriterShmem->requests[BgWriterShmem->num_requests++]; |
| request->rnode = rnode; |
| request->segno = segno; |
| LWLockRelease(BgWriterCommLock); |
| return true; |
| } |
| |
| /* |
| * AbsorbFsyncRequests |
| * Retrieve queued fsync requests and pass them to local smgr. |
| * |
| * This is exported because it must be called during CreateCheckPoint; |
| * we have to be sure we have accepted all pending requests *after* we |
| * establish the checkpoint REDO pointer. Since CreateCheckPoint |
| * sometimes runs in non-bgwriter processes, do nothing if not bgwriter. |
| */ |
| void |
| AbsorbFsyncRequests(void) |
| { |
| BgWriterRequest *requests = NULL; |
| BgWriterRequest *request; |
| int n; |
| |
| if (!am_bg_writer) |
| return; |
| |
| /* |
| * We have to PANIC if we fail to absorb all the pending requests (eg, |
| * because our hashtable runs out of memory). This is because the system |
| * cannot run safely if we are unable to fsync what we have been told to |
| * fsync. Fortunately, the hashtable is so small that the problem is |
| * quite unlikely to arise in practice. |
| */ |
| START_CRIT_SECTION(); |
| |
| /* |
| * We try to avoid holding the lock for a long time by copying the request |
| * array. |
| */ |
| LWLockAcquire(BgWriterCommLock, LW_EXCLUSIVE); |
| |
| n = BgWriterShmem->num_requests; |
| if (n > 0) |
| { |
| requests = (BgWriterRequest *) palloc(n * sizeof(BgWriterRequest)); |
| memcpy(requests, BgWriterShmem->requests, n * sizeof(BgWriterRequest)); |
| } |
| BgWriterShmem->num_requests = 0; |
| |
| LWLockRelease(BgWriterCommLock); |
| |
| for (request = requests; n > 0; request++, n--) |
| RememberFsyncRequest(request->rnode, request->segno); |
| |
| if (requests) |
| pfree(requests); |
| |
| END_CRIT_SECTION(); |
| } |