Add new files for syncrep missed in previous commit

src/backend/replication/syncrep.c

+/*-------------------------------------------------------------------------
+ *
+ * syncrep.c
+ *
+ * Synchronous replication is new as of PostgreSQL 9.1.
+ *
+ * If requested, transaction commits wait until their commit LSN is
+ * acknowledged by the sync standby.
+ *
+ * This module contains the code for waiting and release of backends.
+ * All code in this module executes on the primary. The core streaming
+ * replication transport remains within WALreceiver/WALsender modules.
+ *
+ * The essence of this design is that it isolates all logic about
+ * waiting/releasing onto the primary. The primary defines which standbys
+ * it wishes to wait for. The standby is completely unaware of the
+ * durability requirements of transactions on the primary, reducing the
+ * complexity of the code and streamlining both standby operations and
+ * network bandwidth because there is no requirement to ship
+ * per-transaction state information.
+ *
+ * Replication is either synchronous or not synchronous (async). If it is
+ * async, we just fastpath out of here. If it is sync, then in 9.1 we wait
+ * for the flush location on the standby before releasing the waiting backend.
+ * Further complexity in that interaction is expected in later releases.
+ *
+ * The best performing way to manage the waiting backends is to have a
+ * single ordered queue of waiting backends, so that we can avoid
+ * searching the through all waiters each time we receive a reply.
+ *
+ * In 9.1 we support only a single synchronous standby, chosen from a
+ * priority list of synchronous_standby_names. Before it can become the
+ * synchronous standby it must have caught up with the primary; that may
+ * take some time. Once caught up, the current highest priority standby
+ * will release waiters from the queue.
+ *
+ * Portions Copyright (c) 2010-2011, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  $PostgreSQL$
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <unistd.h>
+
+#include "access/xact.h"
+#include "access/xlog_internal.h"
+#include "miscadmin.h"
+#include "postmaster/autovacuum.h"
+#include "replication/syncrep.h"
+#include "replication/walsender.h"
+#include "storage/latch.h"
+#include "storage/ipc.h"
+#include "storage/pmsignal.h"
+#include "storage/proc.h"
+#include "utils/builtins.h"
+#include "utils/guc.h"
+#include "utils/guc_tables.h"
+#include "utils/memutils.h"
+#include "utils/ps_status.h"
+
+/* User-settable parameters for sync rep */
+bool	sync_rep_mode = false;			/* Only set in user backends */
+char 	*SyncRepStandbyNames;
+
+static bool sync_standbys_defined = false;	/* Is there at least one name? */
+static bool announce_next_takeover = true;
+
+static void SyncRepQueueInsert(void);
+
+static int SyncRepGetStandbyPriority(void);
+static bool SyncRepQueueIsOrderedByLSN(void);
+
+/*
+ * ===========================================================
+ * Synchronous Replication functions for normal user backends
+ * ===========================================================
+ */
+
+/*
+ * Wait for synchronous replication, if requested by user.
+ */
+void
+SyncRepWaitForLSN(XLogRecPtr XactCommitLSN)
+{
+	char 		*new_status = NULL;
+	const char *old_status;
+
+	/*
+	 * Fast exit if user has not requested sync replication, or
+	 * there are no sync replication standby names defined.
+	 * Note that those standbys don't need to be connected.
+	 */
+	if (!SyncRepRequested() || !sync_standbys_defined)
+		return;
+
+	Assert(SHMQueueIsDetached(&(MyProc->syncRepLinks)));
+
+	/*
+	 * Wait for specified LSN to be confirmed.
+	 *
+	 * Each proc has its own wait latch, so we perform a normal latch
+	 * check/wait loop here.
+	 */
+	for (;;)
+	{
+		ResetLatch(&MyProc->waitLatch);
+
+		/*
+		 * Synchronous Replication state machine within user backend
+		 *
+		 * Initially backends start in state SYNC_REP_NOT_WAITING and then
+		 * change that state to SYNC_REP_WAITING before adding ourselves
+		 * to the wait queue. During SyncRepWakeQueue() a WALSender changes
+		 * the state to SYNC_REP_WAIT_COMPLETE once replication is confirmed.
+		 * This backend then resets its state to SYNC_REP_NOT_WAITING when
+		 * we exit normally, or SYNC_REP_MUST_DISCONNECT in abnormal cases.
+		 *
+		 * We read MyProc->syncRepState without SyncRepLock, which
+		 * assumes that read access is atomic.
+		 */
+		switch (MyProc->syncRepState)
+		{
+			case SYNC_REP_NOT_WAITING:
+				/*
+				 * Set our waitLSN so WALSender will know when to wake us.
+				 * We set this before we add ourselves to queue, so that
+				 * any proc on the queue can be examined freely without
+				 * taking a lock on each process in the queue, as long as
+				 * they hold SyncRepLock.
+				 */
+				MyProc->waitLSN = XactCommitLSN;
+				MyProc->syncRepState = SYNC_REP_WAITING;
+
+				/*
+				 * Add to queue while holding lock.
+				 */
+				LWLockAcquire(SyncRepLock, LW_EXCLUSIVE);
+				SyncRepQueueInsert();
+				Assert(SyncRepQueueIsOrderedByLSN());
+				LWLockRelease(SyncRepLock);
+
+				/*
+				 * Alter ps display to show waiting for sync rep.
+				 */
+				if (update_process_title)
+				{
+					int			len;
+
+					old_status = get_ps_display(&len);
+					new_status = (char *) palloc(len + 32 + 1);
+					memcpy(new_status, old_status, len);
+					sprintf(new_status + len, " waiting for %X/%X",
+						 XactCommitLSN.xlogid, XactCommitLSN.xrecoff);
+					set_ps_display(new_status, false);
+					new_status[len] = '\0'; /* truncate off " waiting ..." */
+				}
+
+				break;
+
+			case SYNC_REP_WAITING:
+				/*
+				 * Check for conditions that would cause us to leave the
+				 * wait state before the LSN has been reached.
+				 */
+				if (!PostmasterIsAlive(true))
+				{
+					LWLockAcquire(SyncRepLock, LW_EXCLUSIVE);
+					SHMQueueDelete(&(MyProc->syncRepLinks));
+					LWLockRelease(SyncRepLock);
+
+					MyProc->syncRepState = SYNC_REP_MUST_DISCONNECT;
+					return;
+				}
+
+				/*
+				 * We don't receive SIGHUPs at this point, so resetting
+				 * synchronous_standby_names has no effect on waiters.
+				 */
+
+				/* Continue waiting */
+
+				break;
+
+			case SYNC_REP_WAIT_COMPLETE:
+				/*
+				 * WalSender has checked our LSN and has removed us from
+				 * queue. Cleanup local state and leave.
+				 */
+				Assert(SHMQueueIsDetached(&(MyProc->syncRepLinks)));
+
+				MyProc->syncRepState = SYNC_REP_NOT_WAITING;
+				MyProc->waitLSN.xlogid = 0;
+				MyProc->waitLSN.xrecoff = 0;
+
+				if (new_status)
+				{
+					/* Reset ps display */
+					set_ps_display(new_status, false);
+					pfree(new_status);
+				}
+
+				return;
+
+			case SYNC_REP_MUST_DISCONNECT:
+				return;
+
+			default:
+				elog(FATAL, "invalid syncRepState");
+		}
+
+		/*
+		 * Wait on latch for up to 60 seconds. This allows us to
+		 * check for postmaster death regularly while waiting.
+		 * Note that timeout here does not necessarily release from loop.
+		 */
+		WaitLatch(&MyProc->waitLatch, 60000000L);
+	}
+}
+
+/*
+ * Insert MyProc into SyncRepQueue, maintaining sorted invariant.
+ *
+ * Usually we will go at tail of queue, though its possible that we arrive
+ * here out of order, so start at tail and work back to insertion point.
+ */
+static void
+SyncRepQueueInsert(void)
+{
+	PGPROC	*proc;
+
+	proc = (PGPROC *) SHMQueuePrev(&(WalSndCtl->SyncRepQueue),
+								   &(WalSndCtl->SyncRepQueue),
+								   offsetof(PGPROC, syncRepLinks));
+
+	while (proc)
+	{
+		/*
+		 * Stop at the queue element that we should after to
+		 * ensure the queue is ordered by LSN.
+		 */
+		if (XLByteLT(proc->waitLSN, MyProc->waitLSN))
+			break;
+
+		proc = (PGPROC *) SHMQueuePrev(&(WalSndCtl->SyncRepQueue),
+									   &(proc->syncRepLinks),
+									   offsetof(PGPROC, syncRepLinks));
+	}
+
+	if (proc)
+		SHMQueueInsertAfter(&(proc->syncRepLinks), &(MyProc->syncRepLinks));
+	else
+		SHMQueueInsertAfter(&(WalSndCtl->SyncRepQueue), &(MyProc->syncRepLinks));
+}
+
+void
+SyncRepCleanupAtProcExit(int code, Datum arg)
+{
+	if (!SHMQueueIsDetached(&(MyProc->syncRepLinks)))
+	{
+		LWLockAcquire(SyncRepLock, LW_EXCLUSIVE);
+		SHMQueueDelete(&(MyProc->syncRepLinks));
+		LWLockRelease(SyncRepLock);
+	}
+
+	DisownLatch(&MyProc->waitLatch);
+}
+
+/*
+ * ===========================================================
+ * Synchronous Replication functions for wal sender processes
+ * ===========================================================
+ */
+
+/*
+ * Take any action required to initialise sync rep state from config
+ * data. Called at WALSender startup and after each SIGHUP.
+ */
+void
+SyncRepInitConfig(void)
+{
+	int priority;
+
+	/*
+	 * Determine if we are a potential sync standby and remember the result
+	 * for handling replies from standby.
+	 */
+	priority = SyncRepGetStandbyPriority();
+	if (MyWalSnd->sync_standby_priority != priority)
+	{
+		LWLockAcquire(SyncRepLock, LW_EXCLUSIVE);
+		MyWalSnd->sync_standby_priority = priority;
+		LWLockRelease(SyncRepLock);
+		ereport(DEBUG1,
+				(errmsg("standby \"%s\" now has synchronous standby priority %u",
+						application_name, priority)));
+	}
+}
+
+/*
+ * Update the LSNs on each queue based upon our latest state. This
+ * implements a simple policy of first-valid-standby-releases-waiter.
+ *
+ * Other policies are possible, which would change what we do here and what
+ * perhaps also which information we store as well.
+ */
+void
+SyncRepReleaseWaiters(void)
+{
+	volatile WalSndCtlData *walsndctl = WalSndCtl;
+	volatile WalSnd *syncWalSnd = NULL;
+	int 		numprocs = 0;
+	int			priority = 0;
+	int			i;
+
+	/*
+	 * If this WALSender is serving a standby that is not on the list of
+	 * potential standbys then we have nothing to do. If we are still
+	 * starting up or still running base backup, then leave quickly also.
+	 */
+	if (MyWalSnd->sync_standby_priority == 0 ||
+		MyWalSnd->state < WALSNDSTATE_STREAMING)
+		return;
+
+	/*
+	 * We're a potential sync standby. Release waiters if we are the
+	 * highest priority standby. If there are multiple standbys with
+	 * same priorities then we use the first mentioned standby.
+	 * If you change this, also change pg_stat_get_wal_senders().
+	 */
+	LWLockAcquire(SyncRepLock, LW_EXCLUSIVE);
+
+	for (i = 0; i < max_wal_senders; i++)
+	{
+		/* use volatile pointer to prevent code rearrangement */
+		volatile WalSnd *walsnd = &walsndctl->walsnds[i];
+
+		if (walsnd->pid != 0 &&
+			walsnd->sync_standby_priority > 0 &&
+			(priority == 0 ||
+			 priority > walsnd->sync_standby_priority))
+		{
+			 priority = walsnd->sync_standby_priority;
+			 syncWalSnd = walsnd;
+		}
+	}
+
+	/*
+	 * We should have found ourselves at least.
+	 */
+	Assert(syncWalSnd);
+
+	/*
+	 * If we aren't managing the highest priority standby then just leave.
+	 */
+	if (syncWalSnd != MyWalSnd)
+	{
+		LWLockRelease(SyncRepLock);
+		announce_next_takeover = true;
+		return;
+	}
+
+	if (XLByteLT(walsndctl->lsn, MyWalSnd->flush))
+	{
+		/*
+		 * Set the lsn first so that when we wake backends they will
+		 * release up to this location.
+		 */
+		walsndctl->lsn = MyWalSnd->flush;
+		numprocs = SyncRepWakeQueue(false);
+	}
+
+	LWLockRelease(SyncRepLock);
+
+	elog(DEBUG3, "released %d procs up to %X/%X",
+					numprocs,
+					MyWalSnd->flush.xlogid,
+					MyWalSnd->flush.xrecoff);
+
+	/*
+	 * If we are managing the highest priority standby, though we weren't
+	 * prior to this, then announce we are now the sync standby.
+	 */
+	if (announce_next_takeover)
+	{
+		announce_next_takeover = false;
+		ereport(LOG,
+				(errmsg("standby \"%s\" is now the synchronous standby with priority %u",
+						application_name, MyWalSnd->sync_standby_priority)));
+	}
+}
+
+/*
+ * Check if we are in the list of sync standbys, and if so, determine
+ * priority sequence. Return priority if set, or zero to indicate that
+ * we are not a potential sync standby.
+ *
+ * Compare the parameter SyncRepStandbyNames against the application_name
+ * for this WALSender, or allow any name if we find a wildcard "*".
+ */
+static int
+SyncRepGetStandbyPriority(void)
+{
+	char	   *rawstring;
+	List	   *elemlist;
+	ListCell   *l;
+	int			priority = 0;
+	bool		found = false;
+
+	/* Need a modifiable copy of string */
+	rawstring = pstrdup(SyncRepStandbyNames);
+
+	/* Parse string into list of identifiers */
+	if (!SplitIdentifierString(rawstring, ',', &elemlist))
+	{
+		/* syntax error in list */
+		pfree(rawstring);
+		list_free(elemlist);
+		ereport(FATAL,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+		   errmsg("invalid list syntax for parameter \"synchronous_standby_names\"")));
+		return 0;
+	}
+
+	foreach(l, elemlist)
+	{
+		char	   *standby_name = (char *) lfirst(l);
+
+		priority++;
+
+		if (pg_strcasecmp(standby_name, application_name) == 0 ||
+			pg_strcasecmp(standby_name, "*") == 0)
+		{
+			found = true;
+			break;
+		}
+	}
+
+	pfree(rawstring);
+	list_free(elemlist);
+
+	return (found ? priority : 0);
+}
+
+/*
+ * Walk queue from head setting setting the state of any backends that
+ * need to be woken, remove them from the queue and then wake them.
+ * Set all = true to wake whole queue, or just up to LSN.
+ *
+ * Must hold SyncRepLock.
+ */
+int
+SyncRepWakeQueue(bool all)
+{
+	volatile WalSndCtlData *walsndctl = WalSndCtl;
+	PGPROC	*proc = NULL;
+	PGPROC	*thisproc = NULL;
+	int		numprocs = 0;
+
+	Assert(SyncRepQueueIsOrderedByLSN());
+
+	proc = (PGPROC *) SHMQueueNext(&(WalSndCtl->SyncRepQueue),
+								   &(WalSndCtl->SyncRepQueue),
+								   offsetof(PGPROC, syncRepLinks));
+
+	while (proc)
+	{
+		/*
+		 * Assume the queue is ordered by LSN
+		 */
+		if (!all && XLByteLT(walsndctl->lsn, proc->waitLSN))
+			return numprocs;
+
+		/*
+		 * Move to next proc, so we can delete thisproc from the queue.
+		 * thisproc is valid, proc may be NULL after this.
+		 */
+		thisproc = proc;
+		proc = (PGPROC *) SHMQueueNext(&(WalSndCtl->SyncRepQueue),
+									   &(proc->syncRepLinks),
+									   offsetof(PGPROC, syncRepLinks));
+
+		/*
+		 * Set state to complete; see SyncRepWaitForLSN() for discussion
+		 * of the various states.
+		 */
+		thisproc->syncRepState = SYNC_REP_WAIT_COMPLETE;
+
+		/*
+		 * Remove thisproc from queue.
+		 */
+		SHMQueueDelete(&(thisproc->syncRepLinks));
+
+		/*
+		 * Wake only when we have set state and removed from queue.
+		 */
+		Assert(SHMQueueIsDetached(&(thisproc->syncRepLinks)));
+		Assert(thisproc->syncRepState == SYNC_REP_WAIT_COMPLETE);
+		SetLatch(&(thisproc->waitLatch));
+
+		numprocs++;
+	}
+
+	return numprocs;
+}
+
+#ifdef USE_ASSERT_CHECKING
+static bool
+SyncRepQueueIsOrderedByLSN(void)
+{
+	PGPROC	*proc = NULL;
+	XLogRecPtr lastLSN;
+
+	lastLSN.xlogid = 0;
+	lastLSN.xrecoff = 0;
+
+	proc = (PGPROC *) SHMQueueNext(&(WalSndCtl->SyncRepQueue),
+								   &(WalSndCtl->SyncRepQueue),
+								   offsetof(PGPROC, syncRepLinks));
+
+	while (proc)
+	{
+		/*
+		 * Check the queue is ordered by LSN and that multiple
+		 * procs don't have matching LSNs
+		 */
+		if (XLByteLE(proc->waitLSN, lastLSN))
+			return false;
+
+		lastLSN = proc->waitLSN;
+
+		proc = (PGPROC *) SHMQueueNext(&(WalSndCtl->SyncRepQueue),
+									   &(proc->syncRepLinks),
+									   offsetof(PGPROC, syncRepLinks));
+	}
+
+	return true;
+}
+#endif
+
+/*
+ * ===========================================================
+ * Synchronous Replication functions executed by any process
+ * ===========================================================
+ */
+
+const char *
+assign_synchronous_standby_names(const char *newval, bool doit, GucSource source)
+{
+	char	   *rawstring;
+	List	   *elemlist;
+
+	/* Need a modifiable copy of string */
+	rawstring = pstrdup(newval);
+
+	/* Parse string into list of identifiers */
+	if (!SplitIdentifierString(rawstring, ',', &elemlist))
+	{
+		/* syntax error in list */
+		pfree(rawstring);
+		list_free(elemlist);
+		ereport(FATAL,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+		   errmsg("invalid list syntax for parameter \"synchronous_standby_names\"")));
+		return NULL;
+	}
+
+	/*
+	 * Is there at least one sync standby? If so cache this knowledge to
+	 * improve performance of SyncRepWaitForLSN() for all-async configs.
+	 */
+	if (doit && list_length(elemlist) > 0)
+		sync_standbys_defined = true;
+
+	/*
+	 * Any additional validation of standby names should go here.
+	 *
+	 * Don't attempt to set WALSender priority because this is executed by
+	 * postmaster at startup, not WALSender, so the application_name is
+	 * not yet correctly set.
+	 */
+
+	pfree(rawstring);
+	list_free(elemlist);
+
+	return newval;
+}

src/include/replication/syncrep.h

+/*-------------------------------------------------------------------------
+ *
+ * syncrep.h
+ *	  Exports from replication/syncrep.c.
+ *
+ * Portions Copyright (c) 2010-2010, PostgreSQL Global Development Group
+ *
+ * $PostgreSQL$
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef _SYNCREP_H
+#define _SYNCREP_H
+
+#include "access/xlog.h"
+#include "storage/proc.h"
+#include "storage/shmem.h"
+#include "storage/spin.h"
+#include "utils/guc.h"
+
+#define SyncRepRequested()				(sync_rep_mode)
+
+/* syncRepState */
+#define SYNC_REP_NOT_WAITING		0
+#define SYNC_REP_WAITING			1
+#define SYNC_REP_WAIT_COMPLETE		2
+#define SYNC_REP_MUST_DISCONNECT	3
+
+/* user-settable parameters for synchronous replication */
+extern bool sync_rep_mode;
+extern int 	sync_rep_timeout;
+extern char *SyncRepStandbyNames;
+
+/* called by user backend */
+extern void SyncRepWaitForLSN(XLogRecPtr XactCommitLSN);
+
+/* callback at backend exit */
+extern void SyncRepCleanupAtProcExit(int code, Datum arg);
+
+/* called by wal sender */
+extern void SyncRepInitConfig(void);
+extern void SyncRepReleaseWaiters(void);
+
+/* called by various procs */
+extern int SyncRepWakeQueue(bool all);
+const char *assign_synchronous_standby_names(const char *newval, bool doit, GucSource source);
+
+#endif   /* _SYNCREP_H */