From bf405ba8e460051e715d0a91442b579e590328ce Mon Sep 17 00:00:00 2001
From: Simon Riggs <simon@2ndQuadrant.com>
Date: Tue, 1 Nov 2011 18:07:29 +0000
Subject: [PATCH] Add new file for checkpointer.c
---
src/backend/postmaster/checkpointer.c | 1236 +++++++++++++++++++++++++
1 file changed, 1236 insertions(+)
create mode 100644 src/backend/postmaster/checkpointer.c
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
new file mode 100644
index 0000000000..2e36a0f2f3
--- /dev/null
+++ b/src/backend/postmaster/checkpointer.c
@@ -0,0 +1,1236 @@
+/*-------------------------------------------------------------------------
+ *
+ * checkpointer.c
+ *
+ * The checkpointer is new as of Postgres 9.2. It handles all checkpoints.
+ * Checkpoints are automatically dispatched after a certain amount of time has
+ * elapsed since the last one, and it can be signaled to perform requested
+ * checkpoints as well. (The GUC parameter that mandates a checkpoint every
+ * so many WAL segments is implemented by having backends signal when they
+ * fill WAL segments; the checkpointer itself doesn't watch for the
+ * condition.)
+ *
+ * The checkpointer is started by the postmaster as soon as the startup subprocess
+ * finishes, or as soon as recovery begins if we are doing archive recovery.
+ * It remains alive until the postmaster commands it to terminate.
+ * Normal termination is by SIGUSR2, which instructs the checkpointer 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 checkpointer will simply abort and exit on SIGQUIT.
+ *
+ * If the checkpointer 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) 1996-2011, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ * src/backend/postmaster/checkpointer.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <signal.h>
+#include <sys/time.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "access/xlog_internal.h"
+#include "libpq/pqsignal.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "postmaster/bgwriter.h"
+#include "replication/syncrep.h"
+#include "storage/bufmgr.h"
+#include "storage/ipc.h"
+#include "storage/lwlock.h"
+#include "storage/pmsignal.h"
+#include "storage/shmem.h"
+#include "storage/smgr.h"
+#include "storage/spin.h"
+#include "utils/guc.h"
+#include "utils/memutils.h"
+#include "utils/resowner.h"
+
+
+/*----------
+ * Shared memory area for communication between checkpointer and backends
+ *
+ * The ckpt counters allow backends to watch for completion of a checkpoint
+ * request they send. Here's how it works:
+ * * At start of a checkpoint, checkpointer reads (and clears) the request flags
+ * and increments ckpt_started, while holding ckpt_lck.
+ * * On completion of a checkpoint, checkpointer sets ckpt_done to
+ * equal ckpt_started.
+ * * On failure of a checkpoint, checkpointer increments ckpt_failed
+ * and sets ckpt_done to equal ckpt_started.
+ *
+ * The algorithm for backends is:
+ * 1. Record current values of ckpt_failed and ckpt_started, and
+ * set request flags, while holding ckpt_lck.
+ * 2. Send signal to request checkpoint.
+ * 3. Sleep until ckpt_started changes. Now you know a checkpoint has
+ * begun since you started this algorithm (although *not* that it was
+ * specifically initiated by your signal), and that it is using your flags.
+ * 4. Record new value of ckpt_started.
+ * 5. Sleep until ckpt_done >= saved value of ckpt_started. (Use modulo
+ * arithmetic here in case counters wrap around.) Now you know a
+ * checkpoint has started and completed, but not whether it was
+ * successful.
+ * 6. If ckpt_failed is different from the originally saved value,
+ * assume request failed; otherwise it was definitely successful.
+ *
+ * ckpt_flags holds the OR of the checkpoint request flags sent by all
+ * requesting backends since the last checkpoint start. The flags are
+ * chosen so that OR'ing is the correct way to combine multiple requests.
+ *
+ * num_backend_writes is used to count the number of buffer writes performed
+ * by user backend processes. This counter should be wide enough that it
+ * can't overflow during a single processingbgwriter cycle. num_backend_fsync
+ * counts the subset of those writes that also had to do their own fsync,
+ * because the background writer failed to absorb their request.
+ *
+ * The requests array holds fsync requests sent by backends and not yet
+ * absorbed by the checkpointer.
+ *
+ * Unlike the checkpoint fields, num_backend_writes, num_backend_fsync, and
+ * the requests fields are protected by BgWriterCommLock.
+ *----------
+ */
+typedef struct
+{
+ RelFileNodeBackend rnode;
+ ForkNumber forknum;
+ BlockNumber segno; /* see md.c for special values */
+ /* might add a real request-type field later; not needed yet */
+} BgWriterRequest;
+
+typedef struct
+{
+ pid_t checkpointer_pid; /* PID (0 if not started) */
+
+ slock_t ckpt_lck; /* protects all the ckpt_* fields */
+
+ int ckpt_started; /* advances when checkpoint starts */
+ int ckpt_done; /* advances when checkpoint done */
+ int ckpt_failed; /* advances when checkpoint fails */
+
+ int ckpt_flags; /* checkpoint flags, as defined in xlog.h */
+
+ uint32 num_backend_writes; /* counts user backend buffer writes */
+ uint32 num_backend_fsync; /* counts user backend fsync calls */
+
+ int num_requests; /* current # of requests */
+ int max_requests; /* allocated array size */
+ BgWriterRequest requests[1]; /* VARIABLE LENGTH ARRAY */
+} BgWriterShmemStruct;
+
+static BgWriterShmemStruct *BgWriterShmem;
+
+/* interval for calling AbsorbFsyncRequests in CheckpointWriteDelay */
+#define WRITES_PER_ABSORB 1000
+
+/*
+ * GUC parameters
+ */
+int CheckPointTimeout = 300;
+int CheckPointWarning = 30;
+double CheckPointCompletionTarget = 0.5;
+
+/*
+ * 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_requested = false;
+static volatile sig_atomic_t shutdown_requested = false;
+
+/*
+ * Private state
+ */
+static bool am_checkpointer = false;
+
+static bool ckpt_active = false;
+
+/* these values are valid when ckpt_active is true: */
+static pg_time_t ckpt_start_time;
+static XLogRecPtr ckpt_start_recptr;
+static double ckpt_cached_elapsed;
+
+static pg_time_t last_checkpoint_time;
+static pg_time_t last_xlog_switch_time;
+
+/* Prototypes for private functions */
+
+static void CheckArchiveTimeout(void);
+static bool IsCheckpointOnSchedule(double progress);
+static bool ImmediateCheckpointRequested(void);
+static bool CompactCheckpointerRequestQueue(void);
+
+/* Signal handlers */
+
+static void chkpt_quickdie(SIGNAL_ARGS);
+static void ChkptSigHupHandler(SIGNAL_ARGS);
+static void ReqCheckpointHandler(SIGNAL_ARGS);
+static void ReqShutdownHandler(SIGNAL_ARGS);
+
+
+/*
+ * Main entry point for checkpointer process
+ *
+ * This is invoked from BootstrapMain, which has already created the basic
+ * execution environment, but not enabled signals yet.
+ */
+void
+CheckpointerMain(void)
+{
+ sigjmp_buf local_sigjmp_buf;
+ MemoryContext checkpointer_context;
+
+ BgWriterShmem->checkpointer_pid = MyProcPid;
+ am_checkpointer = true;
+
+ /*
+ * If possible, make this process a group leader, so that the postmaster
+ * can signal any child processes too. (checkpointer 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 signalling.
+ */
+ pqsignal(SIGHUP, ChkptSigHupHandler); /* set flag to read config file */
+ pqsignal(SIGINT, ReqCheckpointHandler); /* request checkpoint */
+ pqsignal(SIGTERM, SIG_IGN); /* ignore SIGTERM */
+ pqsignal(SIGQUIT, chkpt_quickdie); /* hard crash time */
+ 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 */
+ sigdelset(&BlockSig, SIGQUIT);
+
+ /*
+ * Initialize so that first time-driven event happens at the correct time.
+ */
+ last_checkpoint_time = last_xlog_switch_time = (pg_time_t) time(NULL);
+
+ /*
+ * Create a resource owner to keep track of our resources (currently only
+ * buffer pins).
+ */
+ CurrentResourceOwner = ResourceOwnerCreate(NULL, "Checkpointer");
+
+ /*
+ * 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.
+ */
+ checkpointer_context = AllocSetContextCreate(TopMemoryContext,
+ "Checkpointer",
+ ALLOCSET_DEFAULT_MINSIZE,
+ ALLOCSET_DEFAULT_INITSIZE,
+ ALLOCSET_DEFAULT_MAXSIZE);
+ MemoryContextSwitchTo(checkpointer_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 checkpointer, 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);
+
+ /* Warn any waiting backends that the checkpoint failed. */
+ if (ckpt_active)
+ {
+ /* use volatile pointer to prevent code rearrangement */
+ volatile BgWriterShmemStruct *bgs = BgWriterShmem;
+
+ SpinLockAcquire(&bgs->ckpt_lck);
+ bgs->ckpt_failed++;
+ bgs->ckpt_done = bgs->ckpt_started;
+ SpinLockRelease(&bgs->ckpt_lck);
+
+ ckpt_active = false;
+ }
+
+ /*
+ * Now return to normal top-level context and clear ErrorContext for
+ * next time.
+ */
+ MemoryContextSwitchTo(checkpointer_context);
+ FlushErrorState();
+
+ /* Flush any leaked data in the top-level context */
+ MemoryContextResetAndDeleteChildren(checkpointer_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);
+
+ /*
+ * Use the recovery target timeline ID during recovery
+ */
+ if (RecoveryInProgress())
+ ThisTimeLineID = GetRecoveryTargetTLI();
+
+ /* Do this once before starting the loop, then just at SIGHUP time. */
+ SyncRepUpdateSyncStandbysDefined();
+
+ /*
+ * Loop forever
+ */
+ for (;;)
+ {
+ bool do_checkpoint = false;
+ int flags = 0;
+ pg_time_t now;
+ int elapsed_secs;
+
+ /*
+ * Emergency bailout if postmaster has died. This is to avoid the
+ * necessity for manual cleanup of all postmaster children.
+ */
+ if (!PostmasterIsAlive())
+ exit(1);
+
+ /*
+ * Process any requests or signals received recently.
+ */
+ AbsorbFsyncRequests();
+
+ if (got_SIGHUP)
+ {
+ got_SIGHUP = false;
+ ProcessConfigFile(PGC_SIGHUP);
+ /* update global shmem state for sync rep */
+ SyncRepUpdateSyncStandbysDefined();
+ }
+ if (checkpoint_requested)
+ {
+ checkpoint_requested = false;
+ do_checkpoint = true;
+ BgWriterStats.m_requested_checkpoints++;
+ }
+ 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);
+ /* Normal exit from the checkpointer is here */
+ proc_exit(0); /* done */
+ }
+
+ /*
+ * Force a checkpoint if too much time has elapsed since the last one.
+ * Note that we count a timed checkpoint in stats only when this
+ * occurs without an external request, but we set the CAUSE_TIME flag
+ * bit even if there is also an external request.
+ */
+ now = (pg_time_t) time(NULL);
+ elapsed_secs = now - last_checkpoint_time;
+ if (elapsed_secs >= CheckPointTimeout)
+ {
+ if (!do_checkpoint)
+ BgWriterStats.m_timed_checkpoints++;
+ do_checkpoint = true;
+ flags |= CHECKPOINT_CAUSE_TIME;
+ }
+
+ /*
+ * Do a checkpoint if requested.
+ */
+ if (do_checkpoint)
+ {
+ bool ckpt_performed = false;
+ bool do_restartpoint;
+
+ /* use volatile pointer to prevent code rearrangement */
+ volatile BgWriterShmemStruct *bgs = BgWriterShmem;
+
+ /*
+ * Check if we should perform a checkpoint or a restartpoint. As a
+ * side-effect, RecoveryInProgress() initializes TimeLineID if
+ * it's not set yet.
+ */
+ do_restartpoint = RecoveryInProgress();
+
+ /*
+ * Atomically fetch the request flags to figure out what kind of a
+ * checkpoint we should perform, and increase the started-counter
+ * to acknowledge that we've started a new checkpoint.
+ */
+ SpinLockAcquire(&bgs->ckpt_lck);
+ flags |= bgs->ckpt_flags;
+ bgs->ckpt_flags = 0;
+ bgs->ckpt_started++;
+ SpinLockRelease(&bgs->ckpt_lck);
+
+ /*
+ * The end-of-recovery checkpoint is a real checkpoint that's
+ * performed while we're still in recovery.
+ */
+ if (flags & CHECKPOINT_END_OF_RECOVERY)
+ do_restartpoint = false;
+
+ /*
+ * We will warn if (a) too soon since last checkpoint (whatever
+ * caused it) and (b) somebody set the CHECKPOINT_CAUSE_XLOG flag
+ * since the last checkpoint start. Note in particular that this
+ * implementation will not generate warnings caused by
+ * CheckPointTimeout < CheckPointWarning.
+ */
+ if (!do_restartpoint &&
+ (flags & CHECKPOINT_CAUSE_XLOG) &&
+ elapsed_secs < CheckPointWarning)
+ ereport(LOG,
+ (errmsg_plural("checkpoints are occurring too frequently (%d second apart)",
+ "checkpoints are occurring too frequently (%d seconds apart)",
+ elapsed_secs,
+ elapsed_secs),
+ errhint("Consider increasing the configuration parameter \"checkpoint_segments\".")));
+
+ /*
+ * Initialize checkpointer-private variables used during checkpoint.
+ */
+ ckpt_active = true;
+ if (!do_restartpoint)
+ ckpt_start_recptr = GetInsertRecPtr();
+ ckpt_start_time = now;
+ ckpt_cached_elapsed = 0;
+
+ /*
+ * Do the checkpoint.
+ */
+ if (!do_restartpoint)
+ {
+ CreateCheckPoint(flags);
+ ckpt_performed = true;
+ }
+ else
+ ckpt_performed = CreateRestartPoint(flags);
+
+ /*
+ * After any checkpoint, close all smgr files. This is so we
+ * won't hang onto smgr references to deleted files indefinitely.
+ */
+ smgrcloseall();
+
+ /*
+ * Indicate checkpoint completion to any waiting backends.
+ */
+ SpinLockAcquire(&bgs->ckpt_lck);
+ bgs->ckpt_done = bgs->ckpt_started;
+ SpinLockRelease(&bgs->ckpt_lck);
+
+ if (ckpt_performed)
+ {
+ /*
+ * Note we record the checkpoint start time not end time as
+ * last_checkpoint_time. This is so that time-driven
+ * checkpoints happen at a predictable spacing.
+ */
+ last_checkpoint_time = now;
+ }
+ else
+ {
+ /*
+ * We were not able to perform the restartpoint (checkpoints
+ * throw an ERROR in case of error). Most likely because we
+ * have not received any new checkpoint WAL records since the
+ * last restartpoint. Try again in 15 s.
+ */
+ last_checkpoint_time = now - CheckPointTimeout + 15;
+ }
+
+ ckpt_active = false;
+ }
+
+ /*
+ * Nap for a while and then loop again. Later patches will replace
+ * this with a latch loop. Keep it simple now for clarity.
+ * Relatively long sleep because the bgwriter does cleanup now.
+ */
+ pg_usleep(500000L);
+
+ /* Check for archive_timeout and switch xlog files if necessary. */
+ CheckArchiveTimeout();
+ }
+}
+
+/*
+ * CheckArchiveTimeout -- check for archive_timeout and switch xlog files
+ *
+ * This will switch to a new WAL file and force an archive file write
+ * if any activity is recorded in the current WAL file, including just
+ * a single checkpoint record.
+ */
+static void
+CheckArchiveTimeout(void)
+{
+ pg_time_t now;
+ pg_time_t last_time;
+
+ if (XLogArchiveTimeout <= 0 || RecoveryInProgress())
+ return;
+
+ now = (pg_time_t) time(NULL);
+
+ /* First we do a quick check using possibly-stale local state. */
+ if ((int) (now - last_xlog_switch_time) < XLogArchiveTimeout)
+ return;
+
+ /*
+ * Update local state ... note that last_xlog_switch_time is the last time
+ * a switch was performed *or requested*.
+ */
+ last_time = GetLastSegSwitchTime();
+
+ last_xlog_switch_time = Max(last_xlog_switch_time, last_time);
+
+ /* 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;
+ }
+}
+
+/*
+ * Returns true if an immediate checkpoint request is pending. (Note that
+ * this does not check the *current* checkpoint's IMMEDIATE flag, but whether
+ * there is one pending behind it.)
+ */
+static bool
+ImmediateCheckpointRequested(void)
+{
+ if (checkpoint_requested)
+ {
+ volatile BgWriterShmemStruct *bgs = BgWriterShmem;
+
+ /*
+ * We don't need to acquire the ckpt_lck in this case because we're
+ * only looking at a single flag bit.
+ */
+ if (bgs->ckpt_flags & CHECKPOINT_IMMEDIATE)
+ return true;
+ }
+ return false;
+}
+
+/*
+ * CheckpointWriteDelay -- control rate of checkpoint
+ *
+ * This function is called after each page write performed by BufferSync().
+ * It is responsible for throttling BufferSync()'s write rate to hit
+ * checkpoint_completion_target.
+ *
+ * The checkpoint request flags should be passed in; currently the only one
+ * examined is CHECKPOINT_IMMEDIATE, which disables delays between writes.
+ *
+ * 'progress' is an estimate of how much of the work has been done, as a
+ * fraction between 0.0 meaning none, and 1.0 meaning all done.
+ */
+void
+CheckpointWriteDelay(int flags, double progress)
+{
+ static int absorb_counter = WRITES_PER_ABSORB;
+
+ /* Do nothing if checkpoint is being executed by non-checkpointer process */
+ if (!am_checkpointer)
+ return;
+
+ /*
+ * Perform the usual duties and take a nap, unless we're behind
+ * schedule, in which case we just try to catch up as quickly as possible.
+ */
+ if (!(flags & CHECKPOINT_IMMEDIATE) &&
+ !shutdown_requested &&
+ !ImmediateCheckpointRequested() &&
+ IsCheckpointOnSchedule(progress))
+ {
+ if (got_SIGHUP)
+ {
+ got_SIGHUP = false;
+ ProcessConfigFile(PGC_SIGHUP);
+ /* update global shmem state for sync rep */
+ SyncRepUpdateSyncStandbysDefined();
+ }
+
+ AbsorbFsyncRequests();
+ absorb_counter = WRITES_PER_ABSORB;
+
+ CheckArchiveTimeout();
+
+ /*
+ * Checkpoint sleep used to be connected to bgwriter_delay at 200ms.
+ * That resulted in more frequent wakeups if not much work to do.
+ * Checkpointer and bgwriter are no longer related so take the Big Sleep.
+ */
+ pg_usleep(100000L);
+ }
+ else if (--absorb_counter <= 0)
+ {
+ /*
+ * Absorb pending fsync requests after each WRITES_PER_ABSORB write
+ * operations even when we don't sleep, to prevent overflow of the
+ * fsync request queue.
+ */
+ AbsorbFsyncRequests();
+ absorb_counter = WRITES_PER_ABSORB;
+ }
+}
+
+/*
+ * IsCheckpointOnSchedule -- are we on schedule to finish this checkpoint
+ * in time?
+ *
+ * Compares the current progress against the time/segments elapsed since last
+ * checkpoint, and returns true if the progress we've made this far is greater
+ * than the elapsed time/segments.
+ */
+static bool
+IsCheckpointOnSchedule(double progress)
+{
+ XLogRecPtr recptr;
+ struct timeval now;
+ double elapsed_xlogs,
+ elapsed_time;
+
+ Assert(ckpt_active);
+
+ /* Scale progress according to checkpoint_completion_target. */
+ progress *= CheckPointCompletionTarget;
+
+ /*
+ * Check against the cached value first. Only do the more expensive
+ * calculations once we reach the target previously calculated. Since
+ * neither time or WAL insert pointer moves backwards, a freshly
+ * calculated value can only be greater than or equal to the cached value.
+ */
+ if (progress < ckpt_cached_elapsed)
+ return false;
+
+ /*
+ * Check progress against WAL segments written and checkpoint_segments.
+ *
+ * We compare the current WAL insert location against the location
+ * computed before calling CreateCheckPoint. The code in XLogInsert that
+ * actually triggers a checkpoint when checkpoint_segments is exceeded
+ * compares against RedoRecptr, so this is not completely accurate.
+ * However, it's good enough for our purposes, we're only calculating an
+ * estimate anyway.
+ */
+ if (!RecoveryInProgress())
+ {
+ recptr = GetInsertRecPtr();
+ elapsed_xlogs =
+ (((double) (int32) (recptr.xlogid - ckpt_start_recptr.xlogid)) * XLogSegsPerFile +
+ ((double) recptr.xrecoff - (double) ckpt_start_recptr.xrecoff) / XLogSegSize) /
+ CheckPointSegments;
+
+ if (progress < elapsed_xlogs)
+ {
+ ckpt_cached_elapsed = elapsed_xlogs;
+ return false;
+ }
+ }
+
+ /*
+ * Check progress against time elapsed and checkpoint_timeout.
+ */
+ gettimeofday(&now, NULL);
+ elapsed_time = ((double) ((pg_time_t) now.tv_sec - ckpt_start_time) +
+ now.tv_usec / 1000000.0) / CheckPointTimeout;
+
+ if (progress < elapsed_time)
+ {
+ ckpt_cached_elapsed = elapsed_time;
+ return false;
+ }
+
+ /* It looks like we're on schedule. */
+ return true;
+}
+
+
+/* --------------------------------
+ * signal handler routines
+ * --------------------------------
+ */
+
+/*
+ * chkpt_quickdie() occurs when signalled SIGQUIT by the postmaster.
+ *
+ * Some backend has bought the farm,
+ * so we need to stop what we're doing and exit.
+ */
+static void
+chkpt_quickdie(SIGNAL_ARGS)
+{
+ PG_SETMASK(&BlockSig);
+
+ /*
+ * 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.
+ */
+ on_exit_reset();
+
+ /*
+ * 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.)
+ */
+ exit(2);
+}
+
+/* SIGHUP: set flag to re-read config file at next convenient time */
+static void
+ChkptSigHupHandler(SIGNAL_ARGS)
+{
+ got_SIGHUP = true;
+}
+
+/* SIGINT: set flag to run a normal checkpoint right away */
+static void
+ReqCheckpointHandler(SIGNAL_ARGS)
+{
+ checkpoint_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 (!found)
+ {
+ /* First time through, so initialize */
+ MemSet(BgWriterShmem, 0, sizeof(BgWriterShmemStruct));
+ SpinLockInit(&BgWriterShmem->ckpt_lck);
+ BgWriterShmem->max_requests = NBuffers;
+ }
+}
+
+/*
+ * RequestCheckpoint
+ * Called in backend processes to request a checkpoint
+ *
+ * flags is a bitwise OR of the following:
+ * CHECKPOINT_IS_SHUTDOWN: checkpoint is for database shutdown.
+ * CHECKPOINT_END_OF_RECOVERY: checkpoint is for end of WAL recovery.
+ * CHECKPOINT_IMMEDIATE: finish the checkpoint ASAP,
+ * ignoring checkpoint_completion_target parameter.
+ * CHECKPOINT_FORCE: force a checkpoint even if no XLOG activity has occured
+ * since the last one (implied by CHECKPOINT_IS_SHUTDOWN or
+ * CHECKPOINT_END_OF_RECOVERY).
+ * CHECKPOINT_WAIT: wait for completion before returning (otherwise,
+ * just signal bgwriter to do it, and return).
+ * CHECKPOINT_CAUSE_XLOG: checkpoint is requested due to xlog filling.
+ * (This affects logging, and in particular enables CheckPointWarning.)
+ */
+void
+RequestCheckpoint(int flags)
+{
+ /* use volatile pointer to prevent code rearrangement */
+ volatile BgWriterShmemStruct *bgs = BgWriterShmem;
+ int ntries;
+ int old_failed,
+ old_started;
+
+ /*
+ * If in a standalone backend, just do it ourselves.
+ */
+ if (!IsPostmasterEnvironment)
+ {
+ /*
+ * There's no point in doing slow checkpoints in a standalone backend,
+ * because there's no other backends the checkpoint could disrupt.
+ */
+ CreateCheckPoint(flags | CHECKPOINT_IMMEDIATE);
+
+ /*
+ * After any checkpoint, close all smgr files. This is so we won't
+ * hang onto smgr references to deleted files indefinitely.
+ */
+ smgrcloseall();
+
+ return;
+ }
+
+ /*
+ * Atomically set the request flags, and take a snapshot of the counters.
+ * When we see ckpt_started > old_started, we know the flags we set here
+ * have been seen by bgwriter.
+ *
+ * Note that we OR the flags with any existing flags, to avoid overriding
+ * a "stronger" request by another backend. The flag senses must be
+ * chosen to make this work!
+ */
+ SpinLockAcquire(&bgs->ckpt_lck);
+
+ old_failed = bgs->ckpt_failed;
+ old_started = bgs->ckpt_started;
+ bgs->ckpt_flags |= flags;
+
+ SpinLockRelease(&bgs->ckpt_lck);
+
+ /*
+ * Send signal to request checkpoint. It's possible that the bgwriter
+ * hasn't started yet, or is in process of restarting, so we will retry a
+ * few times if needed. Also, if not told to wait for the checkpoint to
+ * occur, we consider failure to send the signal to be nonfatal and merely
+ * LOG it.
+ */
+ for (ntries = 0;; ntries++)
+ {
+ if (BgWriterShmem->checkpointer_pid == 0)
+ {
+ if (ntries >= 20) /* max wait 2.0 sec */
+ {
+ elog((flags & CHECKPOINT_WAIT) ? ERROR : LOG,
+ "could not request checkpoint because checkpointer not running");
+ break;
+ }
+ }
+ else if (kill(BgWriterShmem->checkpointer_pid, SIGINT) != 0)
+ {
+ if (ntries >= 20) /* max wait 2.0 sec */
+ {
+ elog((flags & CHECKPOINT_WAIT) ? ERROR : LOG,
+ "could not signal for checkpoint: %m");
+ break;
+ }
+ }
+ else
+ break; /* signal sent successfully */
+
+ CHECK_FOR_INTERRUPTS();
+ pg_usleep(100000L); /* wait 0.1 sec, then retry */
+ }
+
+ /*
+ * If requested, wait for completion. We detect completion according to
+ * the algorithm given above.
+ */
+ if (flags & CHECKPOINT_WAIT)
+ {
+ int new_started,
+ new_failed;
+
+ /* Wait for a new checkpoint to start. */
+ for (;;)
+ {
+ SpinLockAcquire(&bgs->ckpt_lck);
+ new_started = bgs->ckpt_started;
+ SpinLockRelease(&bgs->ckpt_lck);
+
+ if (new_started != old_started)
+ break;
+
+ CHECK_FOR_INTERRUPTS();
+ pg_usleep(100000L);
+ }
+
+ /*
+ * We are waiting for ckpt_done >= new_started, in a modulo sense.
+ */
+ for (;;)
+ {
+ int new_done;
+
+ SpinLockAcquire(&bgs->ckpt_lck);
+ new_done = bgs->ckpt_done;
+ new_failed = bgs->ckpt_failed;
+ SpinLockRelease(&bgs->ckpt_lck);
+
+ if (new_done - new_started >= 0)
+ break;
+
+ CHECK_FOR_INTERRUPTS();
+ pg_usleep(100000L);
+ }
+
+ if (new_failed != old_failed)
+ ereport(ERROR,
+ (errmsg("checkpoint request failed"),
+ errhint("Consult recent messages in the server log for details.")));
+ }
+}
+
+/*
+ * 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. We also use this
+ * opportunity to count such writes for statistical purposes.
+ *
+ * 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.)
+ *
+ * To avoid holding the lock for longer than necessary, we normally write
+ * to the requests[] queue without checking for duplicates. The bgwriter
+ * will have to eliminate dups internally anyway. However, if we discover
+ * that the queue is full, we make a pass over the entire queue to compact
+ * it. This is somewhat expensive, but the alternative is for the backend
+ * to perform its own fsync, which is far more expensive in practice. It
+ * is theoretically possible a backend fsync might still be necessary, if
+ * the queue is full and contains no duplicate entries. In that case, we
+ * let the backend know by returning false.
+ */
+bool
+ForwardFsyncRequest(RelFileNodeBackend rnode, ForkNumber forknum,
+ BlockNumber segno)
+{
+ BgWriterRequest *request;
+
+ if (!IsUnderPostmaster)
+ return false; /* probably shouldn't even get here */
+
+ if (am_checkpointer)
+ elog(ERROR, "ForwardFsyncRequest must not be called in bgwriter");
+
+ LWLockAcquire(BgWriterCommLock, LW_EXCLUSIVE);
+
+ /* Count all backend writes regardless of if they fit in the queue */
+ BgWriterShmem->num_backend_writes++;
+
+ /*
+ * If the background writer isn't running or the request queue is full,
+ * the backend will have to perform its own fsync request. But before
+ * forcing that to happen, we can try to compact the background writer
+ * request queue.
+ */
+ if (BgWriterShmem->checkpointer_pid == 0 ||
+ (BgWriterShmem->num_requests >= BgWriterShmem->max_requests
+ && !CompactCheckpointerRequestQueue()))
+ {
+ /*
+ * Count the subset of writes where backends have to do their own
+ * fsync
+ */
+ BgWriterShmem->num_backend_fsync++;
+ LWLockRelease(BgWriterCommLock);
+ return false;
+ }
+ request = &BgWriterShmem->requests[BgWriterShmem->num_requests++];
+ request->rnode = rnode;
+ request->forknum = forknum;
+ request->segno = segno;
+ LWLockRelease(BgWriterCommLock);
+ return true;
+}
+
+/*
+ * CompactCheckpointerRequestQueue
+ * Remove duplicates from the request queue to avoid backend fsyncs.
+ *
+ * Although a full fsync request queue is not common, it can lead to severe
+ * performance problems when it does happen. So far, this situation has
+ * only been observed to occur when the system is under heavy write load,
+ * and especially during the "sync" phase of a checkpoint. Without this
+ * logic, each backend begins doing an fsync for every block written, which
+ * gets very expensive and can slow down the whole system.
+ *
+ * Trying to do this every time the queue is full could lose if there
+ * aren't any removable entries. But should be vanishingly rare in
+ * practice: there's one queue entry per shared buffer.
+ */
+static bool
+CompactCheckpointerRequestQueue()
+{
+ struct BgWriterSlotMapping
+ {
+ BgWriterRequest request;
+ int slot;
+ };
+
+ int n,
+ preserve_count;
+ int num_skipped = 0;
+ HASHCTL ctl;
+ HTAB *htab;
+ bool *skip_slot;
+
+ /* must hold BgWriterCommLock in exclusive mode */
+ Assert(LWLockHeldByMe(BgWriterCommLock));
+
+ /* Initialize temporary hash table */
+ MemSet(&ctl, 0, sizeof(ctl));
+ ctl.keysize = sizeof(BgWriterRequest);
+ ctl.entrysize = sizeof(struct BgWriterSlotMapping);
+ ctl.hash = tag_hash;
+ htab = hash_create("CompactBgwriterRequestQueue",
+ BgWriterShmem->num_requests,
+ &ctl,
+ HASH_ELEM | HASH_FUNCTION);
+
+ /* Initialize skip_slot array */
+ skip_slot = palloc0(sizeof(bool) * BgWriterShmem->num_requests);
+
+ /*
+ * The basic idea here is that a request can be skipped if it's followed
+ * by a later, identical request. It might seem more sensible to work
+ * backwards from the end of the queue and check whether a request is
+ * *preceded* by an earlier, identical request, in the hopes of doing less
+ * copying. But that might change the semantics, if there's an
+ * intervening FORGET_RELATION_FSYNC or FORGET_DATABASE_FSYNC request, so
+ * we do it this way. It would be possible to be even smarter if we made
+ * the code below understand the specific semantics of such requests (it
+ * could blow away preceding entries that would end up being canceled
+ * anyhow), but it's not clear that the extra complexity would buy us
+ * anything.
+ */
+ for (n = 0; n < BgWriterShmem->num_requests; ++n)
+ {
+ BgWriterRequest *request;
+ struct BgWriterSlotMapping *slotmap;
+ bool found;
+
+ request = &BgWriterShmem->requests[n];
+ slotmap = hash_search(htab, request, HASH_ENTER, &found);
+ if (found)
+ {
+ skip_slot[slotmap->slot] = true;
+ ++num_skipped;
+ }
+ slotmap->slot = n;
+ }
+
+ /* Done with the hash table. */
+ hash_destroy(htab);
+
+ /* If no duplicates, we're out of luck. */
+ if (!num_skipped)
+ {
+ pfree(skip_slot);
+ return false;
+ }
+
+ /* We found some duplicates; remove them. */
+ for (n = 0, preserve_count = 0; n < BgWriterShmem->num_requests; ++n)
+ {
+ if (skip_slot[n])
+ continue;
+ BgWriterShmem->requests[preserve_count++] = BgWriterShmem->requests[n];
+ }
+ ereport(DEBUG1,
+ (errmsg("compacted fsync request queue from %d entries to %d entries",
+ BgWriterShmem->num_requests, preserve_count)));
+ BgWriterShmem->num_requests = preserve_count;
+
+ /* Cleanup. */
+ pfree(skip_slot);
+ 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 just before
+ * we start fsync'ing. Since CreateCheckPoint sometimes runs in
+ * non-checkpointer processes, do nothing if not checkpointer.
+ */
+void
+AbsorbFsyncRequests(void)
+{
+ BgWriterRequest *requests = NULL;
+ BgWriterRequest *request;
+ int n;
+
+ if (!am_checkpointer)
+ 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);
+
+ /* Transfer write count into pending pgstats message */
+ BgWriterStats.m_buf_written_backend += BgWriterShmem->num_backend_writes;
+ BgWriterStats.m_buf_fsync_backend += BgWriterShmem->num_backend_fsync;
+
+ BgWriterShmem->num_backend_writes = 0;
+ BgWriterShmem->num_backend_fsync = 0;
+
+ 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->forknum, request->segno);
+
+ if (requests)
+ pfree(requests);
+
+ END_CRIT_SECTION();
+}
--
2.24.1