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, 52 insertions, 2 deletions

diff --git a/src/backend/commands/tablespace.c b/src/backend/commands/tablespace.c
index 595fb330b62..cd8c7412898 100644
--- a/src/backend/commands/tablespace.c
+++ b/src/backend/commands/tablespace.c
@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/tablespace.c,v 1.63 2009/11/10 18:53:38 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablespace.c,v 1.64 2009/12/19 01:32:34 sriggs Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -50,6 +50,7 @@
 
 #include "access/heapam.h"
 #include "access/sysattr.h"
+#include "access/transam.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -60,6 +61,8 @@
 #include "miscadmin.h"
 #include "postmaster/bgwriter.h"
 #include "storage/fd.h"
+#include "storage/procarray.h"
+#include "storage/standby.h"
 #include "utils/acl.h"
 #include "utils/builtins.h"
 #include "utils/fmgroids.h"
@@ -1317,11 +1320,58 @@ tblspc_redo(XLogRecPtr lsn, XLogRecord *record)
 	{
 		xl_tblspc_drop_rec *xlrec = (xl_tblspc_drop_rec *) XLogRecGetData(record);
 
+		/*
+		 * If we issued a WAL record for a drop tablespace it is
+		 * because there were no files in it at all. That means that
+		 * no permanent objects can exist in it at this point.
+		 *
+		 * It is possible for standby users to be using this tablespace
+		 * as a location for their temporary files, so if we fail to
+		 * remove all files then do conflict processing and try again,
+		 * if currently enabled.
+		 */
 		if (!remove_tablespace_directories(xlrec->ts_id, true))
-			ereport(ERROR,
+		{
+			VirtualTransactionId *temp_file_users;
+
+			/*
+			 * Standby users may be currently using this tablespace for
+			 * for their temporary files. We only care about current
+			 * users because temp_tablespace parameter will just ignore
+			 * tablespaces that no longer exist.
+			 *
+			 * Ask everybody to cancel their queries immediately so
+			 * we can ensure no temp files remain and we can remove the
+			 * tablespace. Nuke the entire site from orbit, it's the only
+			 * way to be sure.
+			 *
+			 * XXX: We could work out the pids of active backends
+			 * using this tablespace by examining the temp filenames in the
+			 * directory. We would then convert the pids into VirtualXIDs
+			 * before attempting to cancel them.
+			 *
+			 * We don't wait for commit because drop tablespace is
+			 * non-transactional.
+			 */
+			temp_file_users = GetConflictingVirtualXIDs(InvalidTransactionId,
+														InvalidOid,
+														false);
+			ResolveRecoveryConflictWithVirtualXIDs(temp_file_users,
+												   "drop tablespace",
+												   CONFLICT_MODE_ERROR);
+
+			/*
+			 * If we did recovery processing then hopefully the
+			 * backends who wrote temp files should have cleaned up and
+			 * exited by now. So lets recheck before we throw an error.
+			 * If !process_conflicts then this will just fail again.
+			 */
+			if (!remove_tablespace_directories(xlrec->ts_id, true))
+				ereport(ERROR,
 					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 					 errmsg("tablespace %u is not empty",
 							xlrec->ts_id)));
+		}
 	}
 	else
 		elog(PANIC, "tblspc_redo: unknown op code %u", info);