From 00f690a239932e477f25120d19b08aacdc30deb7 Mon Sep 17 00:00:00 2001 From: Fujii Masao Date: Thu, 17 Dec 2020 18:06:51 +0900 Subject: [PATCH] Revert "Get rid of the dedicated latch for signaling the startup process". Revert ac22929a26, as well as the followup fix 113d3591b8. Because it broke the assumption that the startup process waiting for the recovery conflict on buffer pin should be waken up only by buffer unpin or the timeout enabled in ResolveRecoveryConflictWithBufferPin(). It caused, for example, SIGHUP signal handler or walreceiver process to wake that startup process up unnecessarily frequently. Additionally, add the comments about why that dedicated latch that the reverted patch tried to get rid of should not be removed. Thanks to Kyotaro Horiguchi for the discussion. Author: Fujii Masao Discussion: https://postgr.es/m/d8c0c608-021b-3c73-fffd-3240829ee986@oss.nttdata.com --- src/backend/access/transam/xlog.c | 40 +++++++++++++++++++------------ src/backend/postmaster/startup.c | 24 +++++++++++++++---- src/backend/storage/ipc/standby.c | 9 ++++++- 3 files changed, 52 insertions(+), 21 deletions(-) diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index 8dd225c2e1..b1e5d2dbff 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -681,8 +681,18 @@ typedef struct XLogCtlData * recoveryWakeupLatch is used to wake up the startup process to continue * WAL replay, if it is waiting for WAL to arrive or failover trigger file * to appear. + * + * Note that the startup process also uses another latch, its procLatch, + * to wait for recovery conflict. If we get rid of recoveryWakeupLatch for + * signaling the startup process in favor of using its procLatch, which + * comports better with possible generic signal handlers using that latch. + * But we should not do that because the startup process doesn't assume + * that it's waken up by walreceiver process or SIGHUP signal handler + * while it's waiting for recovery conflict. The separate latches, + * recoveryWakeupLatch and procLatch, should be used for inter-process + * communication for WAL replay and recovery conflict, respectively. */ - Latch *recoveryWakeupLatch; + Latch recoveryWakeupLatch; /* * During recovery, we keep a copy of the latest checkpoint record here. @@ -5186,6 +5196,7 @@ XLOGShmemInit(void) SpinLockInit(&XLogCtl->Insert.insertpos_lck); SpinLockInit(&XLogCtl->info_lck); SpinLockInit(&XLogCtl->ulsn_lck); + InitSharedLatch(&XLogCtl->recoveryWakeupLatch); } /* @@ -6121,7 +6132,7 @@ recoveryApplyDelay(XLogReaderState *record) while (true) { - ResetLatch(MyLatch); + ResetLatch(&XLogCtl->recoveryWakeupLatch); /* might change the trigger file's location */ HandleStartupProcInterrupts(); @@ -6140,7 +6151,7 @@ recoveryApplyDelay(XLogReaderState *record) elog(DEBUG2, "recovery apply delay %ld milliseconds", msecs); - (void) WaitLatch(MyLatch, + (void) WaitLatch(&XLogCtl->recoveryWakeupLatch, WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH, msecs, WAIT_EVENT_RECOVERY_APPLY_DELAY); @@ -6469,11 +6480,11 @@ StartupXLOG(void) } /* - * Advertise our latch that other processes can use to wake us up - * if we're going to sleep during recovery. + * Take ownership of the wakeup latch if we're going to sleep during + * recovery. */ if (ArchiveRecoveryRequested) - XLogCtl->recoveryWakeupLatch = &MyProc->procLatch; + OwnLatch(&XLogCtl->recoveryWakeupLatch); /* Set up XLOG reader facility */ MemSet(&private, 0, sizeof(XLogPageReadPrivate)); @@ -7484,11 +7495,11 @@ StartupXLOG(void) ResetUnloggedRelations(UNLOGGED_RELATION_INIT); /* - * We don't need the latch anymore. It's not strictly necessary to reset - * it to NULL, but let's do it for the sake of tidiness. + * We don't need the latch anymore. It's not strictly necessary to disown + * it, but let's do it for the sake of tidiness. */ if (ArchiveRecoveryRequested) - XLogCtl->recoveryWakeupLatch = NULL; + DisownLatch(&XLogCtl->recoveryWakeupLatch); /* * We are now done reading the xlog from stream. Turn off streaming @@ -12300,12 +12311,12 @@ WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess, wait_time = wal_retrieve_retry_interval - TimestampDifferenceMilliseconds(last_fail_time, now); - (void) WaitLatch(MyLatch, + (void) WaitLatch(&XLogCtl->recoveryWakeupLatch, WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH, wait_time, WAIT_EVENT_RECOVERY_RETRIEVE_RETRY_INTERVAL); - ResetLatch(MyLatch); + ResetLatch(&XLogCtl->recoveryWakeupLatch); now = GetCurrentTimestamp(); /* Handle interrupt signals of startup process */ @@ -12559,11 +12570,11 @@ WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess, * to react to a trigger file promptly and to check if the * WAL receiver is still active. */ - (void) WaitLatch(MyLatch, + (void) WaitLatch(&XLogCtl->recoveryWakeupLatch, WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH, 5000L, WAIT_EVENT_RECOVERY_WAL_STREAM); - ResetLatch(MyLatch); + ResetLatch(&XLogCtl->recoveryWakeupLatch); break; } @@ -12735,8 +12746,7 @@ CheckPromoteSignal(void) void WakeupRecovery(void) { - if (XLogCtl->recoveryWakeupLatch) - SetLatch(XLogCtl->recoveryWakeupLatch); + SetLatch(&XLogCtl->recoveryWakeupLatch); } /* diff --git a/src/backend/postmaster/startup.c b/src/backend/postmaster/startup.c index eab9c8c4ed..64af7b8707 100644 --- a/src/backend/postmaster/startup.c +++ b/src/backend/postmaster/startup.c @@ -37,6 +37,7 @@ /* * Flags set by interrupt handlers for later service in the redo loop. */ +static volatile sig_atomic_t got_SIGHUP = false; static volatile sig_atomic_t shutdown_requested = false; static volatile sig_atomic_t promote_signaled = false; @@ -48,6 +49,7 @@ static volatile sig_atomic_t in_restore_command = false; /* Signal handlers */ static void StartupProcTriggerHandler(SIGNAL_ARGS); +static void StartupProcSigHupHandler(SIGNAL_ARGS); /* -------------------------------- @@ -62,7 +64,19 @@ StartupProcTriggerHandler(SIGNAL_ARGS) int save_errno = errno; promote_signaled = true; - SetLatch(MyLatch); + WakeupRecovery(); + + errno = save_errno; +} + +/* SIGHUP: set flag to re-read config file at next convenient time */ +static void +StartupProcSigHupHandler(SIGNAL_ARGS) +{ + int save_errno = errno; + + got_SIGHUP = true; + WakeupRecovery(); errno = save_errno; } @@ -77,7 +91,7 @@ StartupProcShutdownHandler(SIGNAL_ARGS) proc_exit(1); else shutdown_requested = true; - SetLatch(MyLatch); + WakeupRecovery(); errno = save_errno; } @@ -123,9 +137,9 @@ HandleStartupProcInterrupts(void) /* * Process any requests or signals received recently. */ - if (ConfigReloadPending) + if (got_SIGHUP) { - ConfigReloadPending = false; + got_SIGHUP = false; StartupRereadConfig(); } @@ -158,7 +172,7 @@ StartupProcessMain(void) /* * Properly accept or ignore signals the postmaster might send us. */ - pqsignal(SIGHUP, SignalHandlerForConfigReload); /* reload config file */ + pqsignal(SIGHUP, StartupProcSigHupHandler); /* reload config file */ pqsignal(SIGINT, SIG_IGN); /* ignore query cancel */ pqsignal(SIGTERM, StartupProcShutdownHandler); /* request shutdown */ /* SIGQUIT handler was already set up by InitPostmasterChild */ diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c index 4ea3cf1f5c..92d9027776 100644 --- a/src/backend/storage/ipc/standby.c +++ b/src/backend/storage/ipc/standby.c @@ -519,7 +519,14 @@ ResolveRecoveryConflictWithBufferPin(void) enable_timeouts(timeouts, 2); } - /* Wait to be signaled by UnpinBuffer() */ + /* + * Wait to be signaled by UnpinBuffer(). + * + * We assume that only UnpinBuffer() and the timeout requests established + * above can wake us up here. WakeupRecovery() called by walreceiver or + * SIGHUP signal handler, etc cannot do that because it uses the different + * latch from that ProcWaitForSignal() waits on. + */ ProcWaitForSignal(PG_WAIT_BUFFER_PIN); /*