Add new file for checkpointer.c

src/backend/postmaster/checkpointer.c

+/*-------------------------------------------------------------------------
+ *
+ * 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();
+}