Allow read only connections during recovery, known as Hot Standby.

Enabled by recovery_connections = on (default) and forcing archive recovery using a recovery.conf. Recovery processing now emulates the original transactions as they are replayed, providing full locking and MVCC behaviour for read only queries. Recovery must enter consistent state before connections are allowed, so there is a delay, typically short, before connections succeed. Replay of recovering transactions can conflict and in some cases deadlock with queries during recovery; these result in query cancellation after max_standby_delay seconds have expired. Infrastructure changes have minor effects on normal running, though introduce four new types of WAL record.

New test mode "make standbycheck" allows regression tests of static command behaviour on a standby server while in recovery. Typical and extreme dynamic behaviours have been checked via code inspection and manual testing. Few port specific behaviours have been utilised, though primary testing has been on Linux only so far.

This commit is the basic patch. Additional changes will follow in this release to enhance some aspects of behaviour, notably improved handling of conflicts, deadlock detection and query cancellation. Changes to VACUUM FULL are also required.

Simon Riggs, with significant and lengthy review by Heikki Linnakangas, including streamlined redesign of snapshot creation and two-phase commit.

Important contributions from Florian Pflug, Mark Kirkwood, Merlin Moncure, Greg Stark, Gianni Ciolli, Gabriele Bartolini, Hannu Krosing, Robert Haas, Tatsuo Ishii, Hiroyuki Yamada plus support and feedback from many other community members.

1 files changed, 29 insertions, 2 deletions

diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index 10fb728fc79..53e59b59b0e 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/tcop/utility.c,v 1.324 2009/12/15 20:04:49 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/tcop/utility.c,v 1.325 2009/12/19 01:32:36 sriggs Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -351,6 +351,7 @@ standard_ProcessUtility(Node *parsetree,
 						break;
 
 					case TRANS_STMT_PREPARE:
+						PreventCommandDuringRecovery();
 						if (!PrepareTransactionBlock(stmt->gid))
 						{
 							/* report unsuccessful commit in completionTag */
@@ -360,11 +361,13 @@ standard_ProcessUtility(Node *parsetree,
 						break;
 
 					case TRANS_STMT_COMMIT_PREPARED:
+						PreventCommandDuringRecovery();
 						PreventTransactionChain(isTopLevel, "COMMIT PREPARED");
 						FinishPreparedTransaction(stmt->gid, true);
 						break;
 
 					case TRANS_STMT_ROLLBACK_PREPARED:
+						PreventCommandDuringRecovery();
 						PreventTransactionChain(isTopLevel, "ROLLBACK PREPARED");
 						FinishPreparedTransaction(stmt->gid, false);
 						break;
@@ -742,6 +745,7 @@ standard_ProcessUtility(Node *parsetree,
 			break;
 
 		case T_GrantStmt:
+			PreventCommandDuringRecovery();
 			ExecuteGrantStmt((GrantStmt *) parsetree);
 			break;
 
@@ -923,6 +927,7 @@ standard_ProcessUtility(Node *parsetree,
 		case T_NotifyStmt:
 			{
 				NotifyStmt *stmt = (NotifyStmt *) parsetree;
+				PreventCommandDuringRecovery();
 
 				Async_Notify(stmt->conditionname);
 			}
@@ -931,6 +936,7 @@ standard_ProcessUtility(Node *parsetree,
 		case T_ListenStmt:
 			{
 				ListenStmt *stmt = (ListenStmt *) parsetree;
+				PreventCommandDuringRecovery();
 
 				CheckRestrictedOperation("LISTEN");
 				Async_Listen(stmt->conditionname);
@@ -940,6 +946,7 @@ standard_ProcessUtility(Node *parsetree,
 		case T_UnlistenStmt:
 			{
 				UnlistenStmt *stmt = (UnlistenStmt *) parsetree;
+				PreventCommandDuringRecovery();
 
 				CheckRestrictedOperation("UNLISTEN");
 				if (stmt->conditionname)
@@ -960,10 +967,12 @@ standard_ProcessUtility(Node *parsetree,
 			break;
 
 		case T_ClusterStmt:
+			PreventCommandDuringRecovery();
 			cluster((ClusterStmt *) parsetree, isTopLevel);
 			break;
 
 		case T_VacuumStmt:
+			PreventCommandDuringRecovery();
 			vacuum((VacuumStmt *) parsetree, InvalidOid, true, NULL, false,
 				   isTopLevel);
 			break;
@@ -1083,12 +1092,21 @@ standard_ProcessUtility(Node *parsetree,
 				ereport(ERROR,
 						(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 						 errmsg("must be superuser to do CHECKPOINT")));
-			RequestCheckpoint(CHECKPOINT_IMMEDIATE | CHECKPOINT_FORCE | CHECKPOINT_WAIT);
+			/*
+			 * You might think we should have a PreventCommandDuringRecovery()
+			 * here, but we interpret a CHECKPOINT command during recovery
+			 * as a request for a restartpoint instead. We allow this since
+			 * it can be a useful way of reducing switchover time when
+			 * using various forms of replication.
+			 */
+			RequestCheckpoint(CHECKPOINT_IMMEDIATE | CHECKPOINT_WAIT |
+								(RecoveryInProgress() ? 0 : CHECKPOINT_FORCE));
 			break;
 
 		case T_ReindexStmt:
 			{
 				ReindexStmt *stmt = (ReindexStmt *) parsetree;
+				PreventCommandDuringRecovery();
 
 				switch (stmt->kind)
 				{
@@ -2604,3 +2622,12 @@ GetCommandLogLevel(Node *parsetree)
 
 	return lev;
 }
+
+void
+PreventCommandDuringRecovery(void)
+{
+	if (RecoveryInProgress())
+		ereport(ERROR,
+			(errcode(ERRCODE_READ_ONLY_SQL_TRANSACTION),
+			 errmsg("cannot be executed during recovery")));
+}