*** a/src/backend/bootstrap/bootstrap.c
--- b/src/backend/bootstrap/bootstrap.c
***************
*** 315,320 **** AuxiliaryProcessMain(int argc, char *argv[])
--- 315,323 ----
  			case BgWriterProcess:
  				statmsg = "writer process";
  				break;
+ 			case CheckpointerProcess:
+ 				statmsg = "checkpointer process";
+ 				break;
  			case WalWriterProcess:
  				statmsg = "wal writer process";
  				break;
***************
*** 419,424 **** AuxiliaryProcessMain(int argc, char *argv[])
--- 422,432 ----
  			BackgroundWriterMain();
  			proc_exit(1);		/* should never return */
  
+ 		case CheckpointerProcess:
+ 			/* don't set signals, checkpointer has its own agenda */
+ 			CheckpointerMain();
+ 			proc_exit(1);		/* should never return */
+ 
  		case WalWriterProcess:
  			/* don't set signals, walwriter has its own agenda */
  			InitXLOGAccess();
*** a/src/backend/postmaster/Makefile
--- b/src/backend/postmaster/Makefile
***************
*** 13,18 **** top_builddir = ../../..
  include $(top_builddir)/src/Makefile.global
  
  OBJS = autovacuum.o bgwriter.o fork_process.o pgarch.o pgstat.o postmaster.o \
! 	syslogger.o walwriter.o
  
  include $(top_srcdir)/src/backend/common.mk
--- 13,18 ----
  include $(top_builddir)/src/Makefile.global
  
  OBJS = autovacuum.o bgwriter.o fork_process.o pgarch.o pgstat.o postmaster.o \
! 	syslogger.o walwriter.o checkpointer.o
  
  include $(top_srcdir)/src/backend/common.mk
*** a/src/backend/postmaster/bgwriter.c
--- b/src/backend/postmaster/bgwriter.c
***************
*** 10,29 ****
   * still empowered to issue writes if the bgwriter fails to maintain enough
   * clean shared buffers.
   *
!  * The bgwriter is also charged with handling all checkpoints.	It will
!  * automatically dispatch a checkpoint 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 the bgwriter
!  * when they fill WAL segments; the bgwriter itself doesn't watch for the
!  * condition.)
   *
   * The bgwriter 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 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
--- 10,22 ----
   * still empowered to issue writes if the bgwriter fails to maintain enough
   * clean shared buffers.
   *
!  * As of Postgres 9.2 the bgwriter no longer handles checkpoints.
   *
   * The bgwriter 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 bgwriter to exit(0).
!  * 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
***************
*** 54,60 ****
  #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"
--- 47,52 ----
***************
*** 67,162 ****
  #include "utils/resowner.h"
  
  
- /*----------
-  * Shared memory area for communication between bgwriter 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, bgwriter reads (and clears) the request flags
-  *	  and increments ckpt_started, while holding ckpt_lck.
-  *	* On completion of a checkpoint, bgwriter sets ckpt_done to
-  *	  equal ckpt_started.
-  *	* On failure of a checkpoint, bgwriter 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 non-bgwriter processes.  This counter should be wide enough that it
-  * can't overflow during a single bgwriter 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 bgwriter.
-  *
-  * 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		bgwriter_pid;	/* PID of bgwriter (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 non-bgwriter buffer writes */
- 	uint32		num_backend_fsync;		/* counts non-bgwriter 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			BgWriterDelay = 200;
- 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;
  
  /*
--- 59,73 ----
***************
*** 164,192 **** static volatile sig_atomic_t shutdown_requested = false;
   */
  static bool am_bg_writer = 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 void BgWriterNap(void);
- static bool IsCheckpointOnSchedule(double progress);
- static bool ImmediateCheckpointRequested(void);
- static bool CompactBgwriterRequestQueue(void);
  
  /* Signal handlers */
  
  static void bg_quickdie(SIGNAL_ARGS);
  static void BgSigHupHandler(SIGNAL_ARGS);
- static void ReqCheckpointHandler(SIGNAL_ARGS);
  static void ReqShutdownHandler(SIGNAL_ARGS);
  
  
--- 75,88 ----
***************
*** 202,208 **** BackgroundWriterMain(void)
  	sigjmp_buf	local_sigjmp_buf;
  	MemoryContext bgwriter_context;
  
- 	BgWriterShmem->bgwriter_pid = MyProcPid;
  	am_bg_writer = true;
  
  	/*
--- 98,103 ----
***************
*** 228,235 **** BackgroundWriterMain(void)
  	 * process to participate in ProcSignal signalling.
  	 */
  	pqsignal(SIGHUP, BgSigHupHandler);	/* set flag to read config file */
! 	pqsignal(SIGINT, ReqCheckpointHandler);		/* request checkpoint */
! 	pqsignal(SIGTERM, SIG_IGN); /* ignore SIGTERM */
  	pqsignal(SIGQUIT, bg_quickdie);		/* hard crash time */
  	pqsignal(SIGALRM, SIG_IGN);
  	pqsignal(SIGPIPE, SIG_IGN);
--- 123,130 ----
  	 * process to participate in ProcSignal signalling.
  	 */
  	pqsignal(SIGHUP, BgSigHupHandler);	/* set flag to read config file */
! 	pqsignal(SIGINT, SIG_IGN);			/* as of 9.2 no longer requests checkpoint */
! 	pqsignal(SIGTERM, SIG_IGN); 		/* ignore SIGTERM */
  	pqsignal(SIGQUIT, bg_quickdie);		/* hard crash time */
  	pqsignal(SIGALRM, SIG_IGN);
  	pqsignal(SIGPIPE, SIG_IGN);
***************
*** 249,259 **** BackgroundWriterMain(void)
  	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).
  	 */
--- 144,149 ----
***************
*** 305,324 **** BackgroundWriterMain(void)
  		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.
--- 195,200 ----
***************
*** 361,379 **** BackgroundWriterMain(void)
  	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.
--- 237,247 ----
***************
*** 381,403 **** BackgroundWriterMain(void)
  		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)
  		{
--- 249,259 ----
***************
*** 406,547 **** BackgroundWriterMain(void)
  			 * control back to the sigsetjmp block above
  			 */
  			ExitOnAnyError = true;
- 			/* Close down the database */
- 			ShutdownXLOG(0, 0);
  			/* Normal exit from the bgwriter 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, otherwise do one cycle of
! 		 * dirty-buffer writing.
! 		 */
! 		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 bgwriter-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;
! 		}
! 		else
! 			BgBufferSync();
! 
! 		/* Check for archive_timeout and switch xlog files if necessary. */
! 		CheckArchiveTimeout();
  
  		/* Nap for the configured time. */
  		BgWriterNap();
--- 262,275 ----
  			 * control back to the sigsetjmp block above
  			 */
  			ExitOnAnyError = true;
  			/* Normal exit from the bgwriter is here */
  			proc_exit(0);		/* done */
  		}
  
  		/*
! 		 * Do one cycle of dirty-buffer writing.
  		 */
! 		BgBufferSync();
  
  		/* Nap for the configured time. */
  		BgWriterNap();
***************
*** 549,609 **** BackgroundWriterMain(void)
  }
  
  /*
-  * 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;
- 	}
- }
- 
- /*
   * BgWriterNap -- Nap for the configured time or until a signal is received.
   */
  static void
--- 277,282 ----
***************
*** 624,808 **** BgWriterNap(void)
  	 * 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_lru_maxpages > 0 || ckpt_active)
  		udelay = BgWriterDelay * 1000L;
- 	else if (XLogArchiveTimeout > 0)
- 		udelay = 1000000L;		/* One second */
  	else
  		udelay = 10000000L;		/* Ten seconds */
  
  	while (udelay > 999999L)
  	{
! 		if (got_SIGHUP || shutdown_requested ||
! 		(ckpt_active ? ImmediateCheckpointRequested() : checkpoint_requested))
  			break;
  		pg_usleep(1000000L);
- 		AbsorbFsyncRequests();
  		udelay -= 1000000L;
  	}
  
! 	if (!(got_SIGHUP || shutdown_requested ||
! 	  (ckpt_active ? ImmediateCheckpointRequested() : checkpoint_requested)))
  		pg_usleep(udelay);
  }
  
- /*
-  * 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 -- yield control to bgwriter during a checkpoint
-  *
-  * This function is called after each page write performed by BufferSync().
-  * It is responsible for keeping the bgwriter's normal activities in
-  * progress during a long checkpoint, and 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-bgwriter process */
- 	if (!am_bg_writer)
- 		return;
- 
- 	/*
- 	 * Perform the usual bgwriter 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;
- 
- 		BgBufferSync();
- 		CheckArchiveTimeout();
- 		BgWriterNap();
- 	}
- 	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
   * --------------------------------
--- 297,320 ----
  	 * respond reasonably promptly when someone signals us, break down the
  	 * sleep into 1-second increments, and check for interrupts after each
  	 * nap.
  	 */
! 	if (bgwriter_lru_maxpages > 0)
  		udelay = BgWriterDelay * 1000L;
  	else
  		udelay = 10000000L;		/* Ten seconds */
  
  	while (udelay > 999999L)
  	{
! 		if (got_SIGHUP || shutdown_requested)
  			break;
  		pg_usleep(1000000L);
  		udelay -= 1000000L;
  	}
  
! 	if (!(got_SIGHUP || shutdown_requested))
  		pg_usleep(udelay);
  }
  
  /* --------------------------------
   *		signal handler routines
   * --------------------------------
***************
*** 847,1287 **** BgSigHupHandler(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->bgwriter_pid == 0)
- 		{
- 			if (ntries >= 20)	/* max wait 2.0 sec */
- 			{
- 				elog((flags & CHECKPOINT_WAIT) ? ERROR : LOG,
- 				"could not request checkpoint because bgwriter not running");
- 				break;
- 			}
- 		}
- 		else if (kill(BgWriterShmem->bgwriter_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_bg_writer)
- 		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->bgwriter_pid == 0 ||
- 		(BgWriterShmem->num_requests >= BgWriterShmem->max_requests
- 		 && !CompactBgwriterRequestQueue()))
- 	{
- 		/*
- 		 * 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;
- }
- 
- /*
-  * CompactBgwriterRequestQueue
-  *		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
- CompactBgwriterRequestQueue()
- {
- 	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-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);
- 
- 	/* 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();
- }
--- 359,367 ----
*** a/src/backend/postmaster/postmaster.c
--- b/src/backend/postmaster/postmaster.c
***************
*** 206,211 **** bool		restart_after_crash = true;
--- 206,212 ----
  /* PIDs of special child processes; 0 when not running */
  static pid_t StartupPID = 0,
  			BgWriterPID = 0,
+ 			CheckpointerPID = 0,
  			WalWriterPID = 0,
  			WalReceiverPID = 0,
  			AutoVacPID = 0,
***************
*** 277,283 **** typedef enum
  	PM_WAIT_BACKUP,				/* waiting for online backup mode to end */
  	PM_WAIT_READONLY,			/* waiting for read only backends to exit */
  	PM_WAIT_BACKENDS,			/* waiting for live backends to exit */
! 	PM_SHUTDOWN,				/* waiting for bgwriter to do shutdown ckpt */
  	PM_SHUTDOWN_2,				/* waiting for archiver and walsenders to
  								 * finish */
  	PM_WAIT_DEAD_END,			/* waiting for dead_end children to exit */
--- 278,284 ----
  	PM_WAIT_BACKUP,				/* waiting for online backup mode to end */
  	PM_WAIT_READONLY,			/* waiting for read only backends to exit */
  	PM_WAIT_BACKENDS,			/* waiting for live backends to exit */
! 	PM_SHUTDOWN,				/* waiting for checkpointer to do shutdown ckpt */
  	PM_SHUTDOWN_2,				/* waiting for archiver and walsenders to
  								 * finish */
  	PM_WAIT_DEAD_END,			/* waiting for dead_end children to exit */
***************
*** 462,467 **** static void ShmemBackendArrayRemove(Backend *bn);
--- 463,469 ----
  
  #define StartupDataBase()		StartChildProcess(StartupProcess)
  #define StartBackgroundWriter() StartChildProcess(BgWriterProcess)
+ #define StartCheckpointer()		StartChildProcess(CheckpointerProcess)
  #define StartWalWriter()		StartChildProcess(WalWriterProcess)
  #define StartWalReceiver()		StartChildProcess(WalReceiverProcess)
  
***************
*** 1029,1036 **** PostmasterMain(int argc, char *argv[])
  	 * CAUTION: when changing this list, check for side-effects on the signal
  	 * handling setup of child processes.  See tcop/postgres.c,
  	 * bootstrap/bootstrap.c, postmaster/bgwriter.c, postmaster/walwriter.c,
! 	 * postmaster/autovacuum.c, postmaster/pgarch.c, postmaster/pgstat.c, and
! 	 * postmaster/syslogger.c.
  	 */
  	pqinitmask();
  	PG_SETMASK(&BlockSig);
--- 1031,1038 ----
  	 * CAUTION: when changing this list, check for side-effects on the signal
  	 * handling setup of child processes.  See tcop/postgres.c,
  	 * bootstrap/bootstrap.c, postmaster/bgwriter.c, postmaster/walwriter.c,
! 	 * postmaster/autovacuum.c, postmaster/pgarch.c, postmaster/pgstat.c,
! 	 * postmaster/syslogger.c and postmaster/checkpointer.c
  	 */
  	pqinitmask();
  	PG_SETMASK(&BlockSig);
***************
*** 1367,1376 **** ServerLoop(void)
  		 * state that prevents it, start one.  It doesn't matter if this
  		 * fails, we'll just try again later.
  		 */
! 		if (BgWriterPID == 0 &&
! 			(pmState == PM_RUN || pmState == PM_RECOVERY ||
! 			 pmState == PM_HOT_STANDBY))
! 			BgWriterPID = StartBackgroundWriter();
  
  		/*
  		 * Likewise, if we have lost the walwriter process, try to start a new
--- 1369,1382 ----
  		 * state that prevents it, start one.  It doesn't matter if this
  		 * fails, we'll just try again later.
  		 */
! 		if (pmState == PM_RUN || pmState == PM_RECOVERY ||
! 			 pmState == PM_HOT_STANDBY)
! 		{
! 			if (BgWriterPID == 0)
! 				BgWriterPID = StartBackgroundWriter();
! 			if (CheckpointerPID == 0)
! 				CheckpointerPID = StartCheckpointer();
! 		}
  
  		/*
  		 * Likewise, if we have lost the walwriter process, try to start a new
***************
*** 2048,2053 **** SIGHUP_handler(SIGNAL_ARGS)
--- 2054,2061 ----
  			signal_child(StartupPID, SIGHUP);
  		if (BgWriterPID != 0)
  			signal_child(BgWriterPID, SIGHUP);
+ 		if (CheckpointerPID != 0)
+ 			signal_child(CheckpointerPID, SIGHUP);
  		if (WalWriterPID != 0)
  			signal_child(WalWriterPID, SIGHUP);
  		if (WalReceiverPID != 0)
***************
*** 2162,2168 **** pmdie(SIGNAL_ARGS)
  				signal_child(WalReceiverPID, SIGTERM);
  			if (pmState == PM_RECOVERY)
  			{
! 				/* only bgwriter is active in this state */
  				pmState = PM_WAIT_BACKENDS;
  			}
  			else if (pmState == PM_RUN ||
--- 2170,2176 ----
  				signal_child(WalReceiverPID, SIGTERM);
  			if (pmState == PM_RECOVERY)
  			{
! 				/* only checkpointer is active in this state */
  				pmState = PM_WAIT_BACKENDS;
  			}
  			else if (pmState == PM_RUN ||
***************
*** 2207,2212 **** pmdie(SIGNAL_ARGS)
--- 2215,2222 ----
  				signal_child(StartupPID, SIGQUIT);
  			if (BgWriterPID != 0)
  				signal_child(BgWriterPID, SIGQUIT);
+ 			if (CheckpointerPID != 0)
+ 				signal_child(CheckpointerPID, SIGQUIT);
  			if (WalWriterPID != 0)
  				signal_child(WalWriterPID, SIGQUIT);
  			if (WalReceiverPID != 0)
***************
*** 2337,2348 **** reaper(SIGNAL_ARGS)
  			}
  
  			/*
! 			 * Crank up the background writer, if we didn't do that already
  			 * when we entered consistent recovery state.  It doesn't matter
  			 * if this fails, we'll just try again later.
  			 */
  			if (BgWriterPID == 0)
  				BgWriterPID = StartBackgroundWriter();
  
  			/*
  			 * Likewise, start other special children as needed.  In a restart
--- 2347,2360 ----
  			}
  
  			/*
! 			 * Crank up background tasks, if we didn't do that already
  			 * when we entered consistent recovery state.  It doesn't matter
  			 * if this fails, we'll just try again later.
  			 */
  			if (BgWriterPID == 0)
  				BgWriterPID = StartBackgroundWriter();
+ 			if (CheckpointerPID == 0)
+ 				CheckpointerPID = StartCheckpointer();
  
  			/*
  			 * Likewise, start other special children as needed.  In a restart
***************
*** 2370,2379 **** reaper(SIGNAL_ARGS)
  		if (pid == BgWriterPID)
  		{
  			BgWriterPID = 0;
  			if (EXIT_STATUS_0(exitstatus) && pmState == PM_SHUTDOWN)
  			{
  				/*
! 				 * OK, we saw normal exit of the bgwriter after it's been told
  				 * to shut down.  We expect that it wrote a shutdown
  				 * checkpoint.	(If for some reason it didn't, recovery will
  				 * occur on next postmaster start.)
--- 2382,2403 ----
  		if (pid == BgWriterPID)
  		{
  			BgWriterPID = 0;
+ 			if (!EXIT_STATUS_0(exitstatus))
+ 				HandleChildCrash(pid, exitstatus,
+ 								 _("background writer process"));
+ 			continue;
+ 		}
+ 
+ 		/*
+ 		 * Was it the checkpointer?
+ 		 */
+ 		if (pid == CheckpointerPID)
+ 		{
+ 			CheckpointerPID = 0;
  			if (EXIT_STATUS_0(exitstatus) && pmState == PM_SHUTDOWN)
  			{
  				/*
! 				 * OK, we saw normal exit of the checkpointer after it's been told
  				 * to shut down.  We expect that it wrote a shutdown
  				 * checkpoint.	(If for some reason it didn't, recovery will
  				 * occur on next postmaster start.)
***************
*** 2410,2420 **** reaper(SIGNAL_ARGS)
  			else
  			{
  				/*
! 				 * Any unexpected exit of the bgwriter (including FATAL exit)
  				 * is treated as a crash.
  				 */
  				HandleChildCrash(pid, exitstatus,
! 								 _("background writer process"));
  			}
  
  			continue;
--- 2434,2444 ----
  			else
  			{
  				/*
! 				 * Any unexpected exit of the checkpointer (including FATAL exit)
  				 * is treated as a crash.
  				 */
  				HandleChildCrash(pid, exitstatus,
! 								 _("checkpointer process"));
  			}
  
  			continue;
***************
*** 2598,2605 **** CleanupBackend(int pid,
  }
  
  /*
!  * HandleChildCrash -- cleanup after failed backend, bgwriter, walwriter,
!  * or autovacuum.
   *
   * The objectives here are to clean up our local state about the child
   * process, and to signal all other remaining children to quickdie.
--- 2622,2629 ----
  }
  
  /*
!  * HandleChildCrash -- cleanup after failed backend, bgwriter, checkpointer,
!  * walwriter or autovacuum.
   *
   * The objectives here are to clean up our local state about the child
   * process, and to signal all other remaining children to quickdie.
***************
*** 2692,2697 **** HandleChildCrash(int pid, int exitstatus, const char *procname)
--- 2716,2733 ----
  		signal_child(BgWriterPID, (SendStop ? SIGSTOP : SIGQUIT));
  	}
  
+ 	/* Take care of the checkpointer too */
+ 	if (pid == CheckpointerPID)
+ 		CheckpointerPID = 0;
+ 	else if (CheckpointerPID != 0 && !FatalError)
+ 	{
+ 		ereport(DEBUG2,
+ 				(errmsg_internal("sending %s to process %d",
+ 								 (SendStop ? "SIGSTOP" : "SIGQUIT"),
+ 								 (int) CheckpointerPID)));
+ 		signal_child(CheckpointerPID, (SendStop ? SIGSTOP : SIGQUIT));
+ 	}
+ 
  	/* Take care of the walwriter too */
  	if (pid == WalWriterPID)
  		WalWriterPID = 0;
***************
*** 2871,2879 **** PostmasterStateMachine(void)
  	{
  		/*
  		 * PM_WAIT_BACKENDS state ends when we have no regular backends
! 		 * (including autovac workers) and no walwriter or autovac launcher.
! 		 * If we are doing crash recovery then we expect the bgwriter to exit
! 		 * too, otherwise not.	The archiver, stats, and syslogger processes
  		 * are disregarded since they are not connected to shared memory; we
  		 * also disregard dead_end children here. Walsenders are also
  		 * disregarded, they will be terminated later after writing the
--- 2907,2916 ----
  	{
  		/*
  		 * PM_WAIT_BACKENDS state ends when we have no regular backends
! 		 * (including autovac workers) and no walwriter, autovac launcher
! 		 * or bgwriter.  If we are doing crash recovery then we expect the
! 		 * checkpointer to exit as well, otherwise not.	
! 		 * The archiver, stats, and syslogger processes
  		 * are disregarded since they are not connected to shared memory; we
  		 * also disregard dead_end children here. Walsenders are also
  		 * disregarded, they will be terminated later after writing the
***************
*** 2882,2888 **** PostmasterStateMachine(void)
  		if (CountChildren(BACKEND_TYPE_NORMAL | BACKEND_TYPE_AUTOVAC) == 0 &&
  			StartupPID == 0 &&
  			WalReceiverPID == 0 &&
! 			(BgWriterPID == 0 || !FatalError) &&
  			WalWriterPID == 0 &&
  			AutoVacPID == 0)
  		{
--- 2919,2926 ----
  		if (CountChildren(BACKEND_TYPE_NORMAL | BACKEND_TYPE_AUTOVAC) == 0 &&
  			StartupPID == 0 &&
  			WalReceiverPID == 0 &&
! 			BgWriterPID == 0 &&
! 			(CheckpointerPID == 0 || !FatalError) &&
  			WalWriterPID == 0 &&
  			AutoVacPID == 0)
  		{
***************
*** 2904,2925 **** PostmasterStateMachine(void)
  				/*
  				 * If we get here, we are proceeding with normal shutdown. All
  				 * the regular children are gone, and it's time to tell the
! 				 * bgwriter to do a shutdown checkpoint.
  				 */
  				Assert(Shutdown > NoShutdown);
! 				/* Start the bgwriter if not running */
! 				if (BgWriterPID == 0)
! 					BgWriterPID = StartBackgroundWriter();
  				/* And tell it to shut down */
! 				if (BgWriterPID != 0)
  				{
! 					signal_child(BgWriterPID, SIGUSR2);
  					pmState = PM_SHUTDOWN;
  				}
  				else
  				{
  					/*
! 					 * If we failed to fork a bgwriter, just shut down. Any
  					 * required cleanup will happen at next restart. We set
  					 * FatalError so that an "abnormal shutdown" message gets
  					 * logged when we exit.
--- 2942,2963 ----
  				/*
  				 * If we get here, we are proceeding with normal shutdown. All
  				 * the regular children are gone, and it's time to tell the
! 				 * checkpointer to do a shutdown checkpoint.
  				 */
  				Assert(Shutdown > NoShutdown);
! 				/* Start the checkpointer if not running */
! 				if (CheckpointerPID == 0)
! 					CheckpointerPID = StartCheckpointer();
  				/* And tell it to shut down */
! 				if (CheckpointerPID != 0)
  				{
! 					signal_child(CheckpointerPID, SIGUSR2);
  					pmState = PM_SHUTDOWN;
  				}
  				else
  				{
  					/*
! 					 * If we failed to fork a checkpointer, just shut down. Any
  					 * required cleanup will happen at next restart. We set
  					 * FatalError so that an "abnormal shutdown" message gets
  					 * logged when we exit.
***************
*** 2978,2983 **** PostmasterStateMachine(void)
--- 3016,3022 ----
  			Assert(StartupPID == 0);
  			Assert(WalReceiverPID == 0);
  			Assert(BgWriterPID == 0);
+ 			Assert(CheckpointerPID == 0);
  			Assert(WalWriterPID == 0);
  			Assert(AutoVacPID == 0);
  			/* syslogger is not considered here */
***************
*** 4157,4162 **** sigusr1_handler(SIGNAL_ARGS)
--- 4196,4203 ----
  		 */
  		Assert(BgWriterPID == 0);
  		BgWriterPID = StartBackgroundWriter();
+ 		Assert(CheckpointerPID == 0);
+ 		CheckpointerPID = StartCheckpointer();
  
  		pmState = PM_RECOVERY;
  	}
***************
*** 4443,4448 **** StartChildProcess(AuxProcType type)
--- 4484,4493 ----
  				ereport(LOG,
  				   (errmsg("could not fork background writer process: %m")));
  				break;
+ 			case CheckpointerProcess:
+ 				ereport(LOG,
+ 				   (errmsg("could not fork checkpointer process: %m")));
+ 				break;
  			case WalWriterProcess:
  				ereport(LOG,
  						(errmsg("could not fork WAL writer process: %m")));
*** a/src/backend/storage/buffer/bufmgr.c
--- b/src/backend/storage/buffer/bufmgr.c
***************
*** 1278,1288 **** BufferSync(int flags)
  					break;
  
  				/*
! 				 * Perform normal bgwriter duties and sleep to throttle our
! 				 * I/O rate.
  				 */
! 				CheckpointWriteDelay(flags,
! 									 (double) num_written / num_to_write);
  			}
  		}
  
--- 1278,1286 ----
  					break;
  
  				/*
! 				 * Sleep to throttle our I/O rate.
  				 */
! 				CheckpointWriteDelay(flags, num_written, num_to_write);
  			}
  		}
  
*** a/src/backend/storage/smgr/md.c
--- b/src/backend/storage/smgr/md.c
***************
*** 38,44 ****
  /*
   * Special values for the segno arg to RememberFsyncRequest.
   *
!  * Note that CompactBgwriterRequestQueue assumes that it's OK to remove an
   * fsync request from the queue if an identical, subsequent request is found.
   * See comments there before making changes here.
   */
--- 38,44 ----
  /*
   * Special values for the segno arg to RememberFsyncRequest.
   *
!  * Note that CompactcheckpointerRequestQueue assumes that it's OK to remove an
   * fsync request from the queue if an identical, subsequent request is found.
   * See comments there before making changes here.
   */
***************
*** 77,83 ****
   *	Inactive segments are those that once contained data but are currently
   *	not needed because of an mdtruncate() operation.  The reason for leaving
   *	them present at size zero, rather than unlinking them, is that other
!  *	backends and/or the bgwriter might be holding open file references to
   *	such segments.	If the relation expands again after mdtruncate(), such
   *	that a deactivated segment becomes active again, it is important that
   *	such file references still be valid --- else data might get written
--- 77,83 ----
   *	Inactive segments are those that once contained data but are currently
   *	not needed because of an mdtruncate() operation.  The reason for leaving
   *	them present at size zero, rather than unlinking them, is that other
!  *	backends and/or the checkpointer might be holding open file references to
   *	such segments.	If the relation expands again after mdtruncate(), such
   *	that a deactivated segment becomes active again, it is important that
   *	such file references still be valid --- else data might get written
***************
*** 111,117 **** static MemoryContext MdCxt;		/* context for all md.c allocations */
  
  
  /*
!  * In some contexts (currently, standalone backends and the bgwriter process)
   * we keep track of pending fsync operations: we need to remember all relation
   * segments that have been written since the last checkpoint, so that we can
   * fsync them down to disk before completing the next checkpoint.  This hash
--- 111,117 ----
  
  
  /*
!  * In some contexts (currently, standalone backends and the checkpointer process)
   * we keep track of pending fsync operations: we need to remember all relation
   * segments that have been written since the last checkpoint, so that we can
   * fsync them down to disk before completing the next checkpoint.  This hash
***************
*** 123,129 **** static MemoryContext MdCxt;		/* context for all md.c allocations */
   * a hash table, because we don't expect there to be any duplicate requests.
   *
   * (Regular backends do not track pending operations locally, but forward
!  * them to the bgwriter.)
   */
  typedef struct
  {
--- 123,129 ----
   * a hash table, because we don't expect there to be any duplicate requests.
   *
   * (Regular backends do not track pending operations locally, but forward
!  * them to the checkpointer.)
   */
  typedef struct
  {
***************
*** 194,200 **** mdinit(void)
  	 * Create pending-operations hashtable if we need it.  Currently, we need
  	 * it if we are standalone (not under a postmaster) OR if we are a
  	 * bootstrap-mode subprocess of a postmaster (that is, a startup or
! 	 * bgwriter process).
  	 */
  	if (!IsUnderPostmaster || IsBootstrapProcessingMode())
  	{
--- 194,200 ----
  	 * Create pending-operations hashtable if we need it.  Currently, we need
  	 * it if we are standalone (not under a postmaster) OR if we are a
  	 * bootstrap-mode subprocess of a postmaster (that is, a startup or
! 	 * checkpointer process).
  	 */
  	if (!IsUnderPostmaster || IsBootstrapProcessingMode())
  	{
***************
*** 214,223 **** mdinit(void)
  }
  
  /*
!  * In archive recovery, we rely on bgwriter to do fsyncs, but we will have
   * already created the pendingOpsTable during initialization of the startup
   * process.  Calling this function drops the local pendingOpsTable so that
!  * subsequent requests will be forwarded to bgwriter.
   */
  void
  SetForwardFsyncRequests(void)
--- 214,223 ----
  }
  
  /*
!  * In archive recovery, we rely on checkpointer to do fsyncs, but we will have
   * already created the pendingOpsTable during initialization of the startup
   * process.  Calling this function drops the local pendingOpsTable so that
!  * subsequent requests will be forwarded to checkpointer.
   */
  void
  SetForwardFsyncRequests(void)
***************
*** 765,773 **** mdnblocks(SMgrRelation reln, ForkNumber forknum)
  	 * NOTE: this assumption could only be wrong if another backend has
  	 * truncated the relation.	We rely on higher code levels to handle that
  	 * scenario by closing and re-opening the md fd, which is handled via
! 	 * relcache flush.	(Since the bgwriter doesn't participate in relcache
  	 * flush, it could have segment chain entries for inactive segments;
! 	 * that's OK because the bgwriter never needs to compute relation size.)
  	 */
  	while (v->mdfd_chain != NULL)
  	{
--- 765,773 ----
  	 * NOTE: this assumption could only be wrong if another backend has
  	 * truncated the relation.	We rely on higher code levels to handle that
  	 * scenario by closing and re-opening the md fd, which is handled via
! 	 * relcache flush.	(Since the checkpointer doesn't participate in relcache
  	 * flush, it could have segment chain entries for inactive segments;
! 	 * that's OK because the checkpointer never needs to compute relation size.)
  	 */
  	while (v->mdfd_chain != NULL)
  	{
***************
*** 957,963 **** mdsync(void)
  		elog(ERROR, "cannot sync without a pendingOpsTable");
  
  	/*
! 	 * If we are in the bgwriter, the sync had better include all fsync
  	 * requests that were queued by backends up to this point.	The tightest
  	 * race condition that could occur is that a buffer that must be written
  	 * and fsync'd for the checkpoint could have been dumped by a backend just
--- 957,963 ----
  		elog(ERROR, "cannot sync without a pendingOpsTable");
  
  	/*
! 	 * If we are in the checkpointer, the sync had better include all fsync
  	 * requests that were queued by backends up to this point.	The tightest
  	 * race condition that could occur is that a buffer that must be written
  	 * and fsync'd for the checkpoint could have been dumped by a backend just
***************
*** 1033,1039 **** mdsync(void)
  			int			failures;
  
  			/*
! 			 * If in bgwriter, we want to absorb pending requests every so
  			 * often to prevent overflow of the fsync request queue.  It is
  			 * unspecified whether newly-added entries will be visited by
  			 * hash_seq_search, but we don't care since we don't need to
--- 1033,1039 ----
  			int			failures;
  
  			/*
! 			 * If in checkpointer, we want to absorb pending requests every so
  			 * often to prevent overflow of the fsync request queue.  It is
  			 * unspecified whether newly-added entries will be visited by
  			 * hash_seq_search, but we don't care since we don't need to
***************
*** 1070,1078 **** mdsync(void)
  				 * say "but an unreferenced SMgrRelation is still a leak!" Not
  				 * really, because the only case in which a checkpoint is done
  				 * by a process that isn't about to shut down is in the
! 				 * bgwriter, and it will periodically do smgrcloseall(). This
  				 * fact justifies our not closing the reln in the success path
! 				 * either, which is a good thing since in non-bgwriter cases
  				 * we couldn't safely do that.)  Furthermore, in many cases
  				 * the relation will have been dirtied through this same smgr
  				 * relation, and so we can save a file open/close cycle.
--- 1070,1078 ----
  				 * say "but an unreferenced SMgrRelation is still a leak!" Not
  				 * really, because the only case in which a checkpoint is done
  				 * by a process that isn't about to shut down is in the
! 				 * checkpointer, and it will periodically do smgrcloseall(). This
  				 * fact justifies our not closing the reln in the success path
! 				 * either, which is a good thing since in non-checkpointer cases
  				 * we couldn't safely do that.)  Furthermore, in many cases
  				 * the relation will have been dirtied through this same smgr
  				 * relation, and so we can save a file open/close cycle.
***************
*** 1301,1307 **** register_unlink(RelFileNodeBackend rnode)
  	else
  	{
  		/*
! 		 * Notify the bgwriter about it.  If we fail to queue the request
  		 * message, we have to sleep and try again, because we can't simply
  		 * delete the file now.  Ugly, but hopefully won't happen often.
  		 *
--- 1301,1307 ----
  	else
  	{
  		/*
! 		 * Notify the checkpointer about it.  If we fail to queue the request
  		 * message, we have to sleep and try again, because we can't simply
  		 * delete the file now.  Ugly, but hopefully won't happen often.
  		 *
***************
*** 1315,1324 **** register_unlink(RelFileNodeBackend rnode)
  }
  
  /*
!  * RememberFsyncRequest() -- callback from bgwriter side of fsync request
   *
   * We stuff most fsync requests into the local hash table for execution
!  * during the bgwriter's next checkpoint.  UNLINK requests go into a
   * separate linked list, however, because they get processed separately.
   *
   * The range of possible segment numbers is way less than the range of
--- 1315,1324 ----
  }
  
  /*
!  * RememberFsyncRequest() -- callback from checkpointer side of fsync request
   *
   * We stuff most fsync requests into the local hash table for execution
!  * during the checkpointer's next checkpoint.  UNLINK requests go into a
   * separate linked list, however, because they get processed separately.
   *
   * The range of possible segment numbers is way less than the range of
***************
*** 1460,1479 **** ForgetRelationFsyncRequests(RelFileNodeBackend rnode, ForkNumber forknum)
  	else if (IsUnderPostmaster)
  	{
  		/*
! 		 * Notify the bgwriter about it.  If we fail to queue the revoke
  		 * message, we have to sleep and try again ... ugly, but hopefully
  		 * won't happen often.
  		 *
  		 * XXX should we CHECK_FOR_INTERRUPTS in this loop?  Escaping with an
  		 * error would leave the no-longer-used file still present on disk,
! 		 * which would be bad, so I'm inclined to assume that the bgwriter
  		 * will always empty the queue soon.
  		 */
  		while (!ForwardFsyncRequest(rnode, forknum, FORGET_RELATION_FSYNC))
  			pg_usleep(10000L);	/* 10 msec seems a good number */
  
  		/*
! 		 * Note we don't wait for the bgwriter to actually absorb the revoke
  		 * message; see mdsync() for the implications.
  		 */
  	}
--- 1460,1479 ----
  	else if (IsUnderPostmaster)
  	{
  		/*
! 		 * Notify the checkpointer about it.  If we fail to queue the revoke
  		 * message, we have to sleep and try again ... ugly, but hopefully
  		 * won't happen often.
  		 *
  		 * XXX should we CHECK_FOR_INTERRUPTS in this loop?  Escaping with an
  		 * error would leave the no-longer-used file still present on disk,
! 		 * which would be bad, so I'm inclined to assume that the checkpointer
  		 * will always empty the queue soon.
  		 */
  		while (!ForwardFsyncRequest(rnode, forknum, FORGET_RELATION_FSYNC))
  			pg_usleep(10000L);	/* 10 msec seems a good number */
  
  		/*
! 		 * Note we don't wait for the checkpointer to actually absorb the revoke
  		 * message; see mdsync() for the implications.
  		 */
  	}
*** a/src/include/access/xlog_internal.h
--- b/src/include/access/xlog_internal.h
***************
*** 256,262 **** typedef struct RmgrData
  extern const RmgrData RmgrTable[];
  
  /*
!  * Exported to support xlog switching from bgwriter
   */
  extern pg_time_t GetLastSegSwitchTime(void);
  extern XLogRecPtr RequestXLogSwitch(void);
--- 256,262 ----
  extern const RmgrData RmgrTable[];
  
  /*
!  * Exported to support xlog switching from checkpointer
   */
  extern pg_time_t GetLastSegSwitchTime(void);
  extern XLogRecPtr RequestXLogSwitch(void);
*** a/src/include/bootstrap/bootstrap.h
--- b/src/include/bootstrap/bootstrap.h
***************
*** 22,27 **** typedef enum
--- 22,28 ----
  	BootstrapProcess,
  	StartupProcess,
  	BgWriterProcess,
+ 	CheckpointerProcess,
  	WalWriterProcess,
  	WalReceiverProcess,
  
*** a/src/include/postmaster/bgwriter.h
--- b/src/include/postmaster/bgwriter.h
***************
*** 23,31 **** extern int	CheckPointWarning;
  extern double CheckPointCompletionTarget;
  
  extern void BackgroundWriterMain(void);
  
  extern void RequestCheckpoint(int flags);
! extern void CheckpointWriteDelay(int flags, double progress);
  
  extern bool ForwardFsyncRequest(RelFileNodeBackend rnode, ForkNumber forknum,
  					BlockNumber segno);
--- 23,32 ----
  extern double CheckPointCompletionTarget;
  
  extern void BackgroundWriterMain(void);
+ extern void CheckpointerMain(void);
  
  extern void RequestCheckpoint(int flags);
! extern void CheckpointWriteDelay(int flags, int num_written, int num_to_write);
  
  extern bool ForwardFsyncRequest(RelFileNodeBackend rnode, ForkNumber forknum,
  					BlockNumber segno);
*** a/src/include/storage/proc.h
--- b/src/include/storage/proc.h
***************
*** 190,200 **** extern PROC_HDR *ProcGlobal;
   * We set aside some extra PGPROC structures for auxiliary processes,
   * ie things that aren't full-fledged backends but need shmem access.
   *
!  * Background writer and WAL writer run during normal operation. Startup
!  * process and WAL receiver also consume 2 slots, but WAL writer is
!  * launched only after startup has exited, so we only need 3 slots.
   */
! #define NUM_AUXILIARY_PROCS		3
  
  
  /* configurable options */
--- 190,200 ----
   * We set aside some extra PGPROC structures for auxiliary processes,
   * ie things that aren't full-fledged backends but need shmem access.
   *
!  * Background writer, checkpointer and WAL writer run during normal operation.
!  * Startup process and WAL receiver also consume 2 slots, but WAL writer is
!  * launched only after startup has exited, so we only need 4 slots.
   */
! #define NUM_AUXILIARY_PROCS		4
  
  
  /* configurable options */
*** a/src/include/storage/procsignal.h
--- b/src/include/storage/procsignal.h
***************
*** 19,25 ****
  
  /*
   * Reasons for signalling a Postgres child process (a backend or an auxiliary
!  * process, like bgwriter).  We can cope with concurrent signals for different
   * reasons.  However, if the same reason is signaled multiple times in quick
   * succession, the process is likely to observe only one notification of it.
   * This is okay for the present uses.
--- 19,25 ----
  
  /*
   * Reasons for signalling a Postgres child process (a backend or an auxiliary
!  * process, like checkpointer).  We can cope with concurrent signals for different
   * reasons.  However, if the same reason is signaled multiple times in quick
   * succession, the process is likely to observe only one notification of it.
   * This is okay for the present uses.