Change the relation_open protocol so that we obtain lock on a relation

(table or index) before trying to open its relcache entry.  This fixes
race conditions in which someone else commits a change to the relation's
catalog entries while we are in process of doing relcache load.  Problems
of that ilk have been reported sporadically for years, but it was not
really practical to fix until recently --- for instance, the recent
addition of WAL-log support for in-place updates helped.

Along the way, remove pg_am.amconcurrent: all AMs are now expected to support
concurrent update.

7 files changed, 51 insertions, 87 deletions

diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index e16afa0559d..f0cbaefd60e 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/cluster.c,v 1.151 2006/07/31 01:16:37 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/cluster.c,v 1.152 2006/07/31 20:09:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -314,8 +314,7 @@ check_index_is_clusterable(Relation OldHeap, Oid indexOid, bool recheck)
 {
 	Relation	OldIndex;
 
-	OldIndex = index_open(indexOid);
-	LockRelation(OldIndex, AccessExclusiveLock);
+	OldIndex = index_open(indexOid, AccessExclusiveLock);
 
 	/*
 	 * Check that index is in fact an index on the given relation
@@ -406,7 +405,7 @@ check_index_is_clusterable(Relation OldHeap, Oid indexOid, bool recheck)
 			   errmsg("cannot cluster temporary tables of other sessions")));
 
 	/* Drop relcache refcnt on OldIndex, but keep lock */
-	index_close(OldIndex);
+	index_close(OldIndex, NoLock);
 }
 
 /*
@@ -649,7 +648,7 @@ copy_heap_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex)
 	 */
 	NewHeap = heap_open(OIDNewHeap, AccessExclusiveLock);
 	OldHeap = heap_open(OIDOldHeap, AccessExclusiveLock);
-	OldIndex = index_open(OIDOldIndex);
+	OldIndex = index_open(OIDOldIndex, AccessExclusiveLock);
 
 	/*
 	 * Their tuple descriptors should be exactly alike, but here we only need
@@ -669,7 +668,7 @@ copy_heap_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex)
 	 * Scan through the OldHeap on the OldIndex and copy each tuple into the
 	 * NewHeap.
 	 */
-	scan = index_beginscan(OldHeap, OldIndex, true,
+	scan = index_beginscan(OldHeap, OldIndex,
 						   SnapshotNow, 0, (ScanKey) NULL);
 
 	while ((tuple = index_getnext(scan, ForwardScanDirection)) != NULL)
@@ -724,7 +723,7 @@ copy_heap_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex)
 	pfree(values);
 	pfree(nulls);
 
-	index_close(OldIndex);
+	index_close(OldIndex, NoLock);
 	heap_close(OldHeap, NoLock);
 	heap_close(NewHeap, NoLock);
 }
diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index a3b35a640ea..6154a4ed3da 100644
--- a/src/backend/commands/sequence.c
+++ b/src/backend/commands/sequence.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/sequence.c,v 1.137 2006/07/14 14:52:18 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/sequence.c,v 1.138 2006/07/31 20:09:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -79,7 +79,7 @@ static SeqTable seqtab = NULL;	/* Head of list of SeqTable items */
 static SeqTableData *last_used_seq = NULL;
 
 static int64 nextval_internal(Oid relid);
-static void acquire_share_lock(Relation seqrel, SeqTable seq);
+static Relation open_share_lock(SeqTable seq);
 static void init_sequence(Oid relid, SeqTable *p_elm, Relation *p_rel);
 static Form_pg_sequence read_info(SeqTable elm, Relation rel, Buffer *buf);
 static void init_params(List *options, Form_pg_sequence new, bool isInit);
@@ -650,8 +650,7 @@ lastval(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("lastval is not yet defined in this session")));
 
-	seqrel = relation_open(last_used_seq->relid, NoLock);
-	acquire_share_lock(seqrel, last_used_seq);
+	seqrel = open_share_lock(last_used_seq);
 
 	/* nextval() must have already been called for this sequence */
 	Assert(last_used_seq->increment != 0);
@@ -802,16 +801,19 @@ setval3_oid(PG_FUNCTION_ARGS)
 
 
 /*
+ * Open the sequence and acquire AccessShareLock if needed
+ *
  * If we haven't touched the sequence already in this transaction,
  * we need to acquire AccessShareLock.	We arrange for the lock to
  * be owned by the top transaction, so that we don't need to do it
  * more than once per xact.
  */
-static void
-acquire_share_lock(Relation seqrel, SeqTable seq)
+static Relation
+open_share_lock(SeqTable seq)
 {
 	TransactionId thisxid = GetTopTransactionId();
 
+	/* Get the lock if not already held in this xact */
 	if (seq->xid != thisxid)
 	{
 		ResourceOwner currentOwner;
@@ -820,7 +822,7 @@ acquire_share_lock(Relation seqrel, SeqTable seq)
 		PG_TRY();
 		{
 			CurrentResourceOwner = TopTransactionResourceOwner;
-			LockRelation(seqrel, AccessShareLock);
+			LockRelationOid(seq->relid, AccessShareLock);
 		}
 		PG_CATCH();
 		{
@@ -831,9 +833,12 @@ acquire_share_lock(Relation seqrel, SeqTable seq)
 		PG_END_TRY();
 		CurrentResourceOwner = currentOwner;
 
-		/* Flag that we have a lock in the current xact. */
+		/* Flag that we have a lock in the current xact */
 		seq->xid = thisxid;
 	}
+
+	/* We now know we have AccessShareLock, and can safely open the rel */
+	return relation_open(seq->relid, NoLock);
 }
 
 /*
@@ -843,19 +848,8 @@ acquire_share_lock(Relation seqrel, SeqTable seq)
 static void
 init_sequence(Oid relid, SeqTable *p_elm, Relation *p_rel)
 {
+	SeqTable elm;
 	Relation	seqrel;
-	volatile SeqTable elm;
-
-	/*
-	 * Open the sequence relation.
-	 */
-	seqrel = relation_open(relid, NoLock);
-
-	if (seqrel->rd_rel->relkind != RELKIND_SEQUENCE)
-		ereport(ERROR,
-				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("\"%s\" is not a sequence",
-						RelationGetRelationName(seqrel))));
 
 	/* Look to see if we already have a seqtable entry for relation */
 	for (elm = seqtab; elm != NULL; elm = elm->next)
@@ -890,7 +884,16 @@ init_sequence(Oid relid, SeqTable *p_elm, Relation *p_rel)
 		seqtab = elm;
 	}
 
-	acquire_share_lock(seqrel, elm);
+	/*
+	 * Open the sequence relation.
+	 */
+	seqrel = open_share_lock(elm);
+
+	if (seqrel->rd_rel->relkind != RELKIND_SEQUENCE)
+		ereport(ERROR,
+				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				 errmsg("\"%s\" is not a sequence",
+						RelationGetRelationName(seqrel))));
 
 	*p_elm = elm;
 	*p_rel = seqrel;
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 53382ff3d47..3b408b411a6 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.197 2006/07/31 01:16:37 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.198 2006/07/31 20:09:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -5863,7 +5863,10 @@ ATExecSetTableSpace(Oid tableOid, Oid newTableSpace)
 	HeapTuple	tuple;
 	Form_pg_class rd_rel;
 
-	rel = relation_open(tableOid, NoLock);
+	/*
+	 * Need lock here in case we are recursing to toast table or index
+	 */
+	rel = relation_open(tableOid, AccessExclusiveLock);
 
 	/*
 	 * We can never allow moving of shared or nailed-in-cache relations,
diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index 158e783c575..13e7cab721b 100644
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.204 2006/07/14 14:52:18 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.205 2006/07/31 20:09:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -36,7 +36,6 @@
 #include "utils/inval.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
-#include "utils/relcache.h"
 #include "utils/syscache.h"
 
 
@@ -2986,7 +2985,6 @@ AfterTriggerSetState(ConstraintsSetStmt *stmt)
 				while (HeapTupleIsValid(htup = systable_getnext(tgscan)))
 				{
 					Form_pg_trigger pg_trigger = (Form_pg_trigger) GETSTRUCT(htup);
-					Relation constraintRel;
 					Oid constraintNamespaceId;
 
 					/*
@@ -3010,13 +3008,9 @@ AfterTriggerSetState(ConstraintsSetStmt *stmt)
 						pg_trigger->tgfoid == F_RI_FKEY_SETNULL_DEL ||
 						pg_trigger->tgfoid == F_RI_FKEY_SETDEFAULT_UPD ||
 						pg_trigger->tgfoid == F_RI_FKEY_SETDEFAULT_DEL)
-					{
-						constraintRel = RelationIdGetRelation(pg_trigger->tgconstrrelid);
-					} else {
-						constraintRel = RelationIdGetRelation(pg_trigger->tgrelid);
-					}
-					constraintNamespaceId = RelationGetNamespace(constraintRel);
-					RelationClose(constraintRel);
+						constraintNamespaceId = get_rel_namespace(pg_trigger->tgconstrrelid);
+					else
+						constraintNamespaceId = get_rel_namespace(pg_trigger->tgrelid);
 
 					/*
 					 * If this constraint is not in the schema we're
diff --git a/src/backend/commands/typecmds.c b/src/backend/commands/typecmds.c
index 1304e686813..6dfa6296d5a 100644
--- a/src/backend/commands/typecmds.c
+++ b/src/backend/commands/typecmds.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/typecmds.c,v 1.95 2006/07/14 14:52:18 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/typecmds.c,v 1.96 2006/07/31 20:09:00 tgl Exp $
  *
  * DESCRIPTION
  *	  The "DefineFoo" routines take the parse tree and pick out the
@@ -1625,6 +1625,8 @@ get_rels_with_domain(Oid domainOid, LOCKMODE lockmode)
 	SysScanDesc depScan;
 	HeapTuple	depTup;
 
+	Assert(lockmode != NoLock);
+
 	/*
 	 * We scan pg_depend to find those things that depend on the domain. (We
 	 * assume we can ignore refobjsubid for a domain.)
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index eb0fce72edb..c21be2f4788 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -13,7 +13,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.336 2006/07/30 02:07:18 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.337 2006/07/31 20:09:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1138,7 +1138,7 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 	 * same process.
 	 */
 	onerelid = onerel->rd_lockInfo.lockRelId;
-	LockRelationForSession(&onerelid, onerel->rd_istemp, lmode);
+	LockRelationIdForSession(&onerelid, lmode);
 
 	/*
 	 * Remember the relation's TOAST relation for later
@@ -1175,7 +1175,7 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 	/*
 	 * Now release the session-level lock on the master table.
 	 */
-	UnlockRelationForSession(&onerelid, lmode);
+	UnlockRelationIdForSession(&onerelid, lmode);
 
 	return;
 }
@@ -3476,6 +3476,8 @@ vac_open_indexes(Relation relation, LOCKMODE lockmode,
 	ListCell   *indexoidscan;
 	int			i;
 
+	Assert(lockmode != NoLock);
+
 	indexoidlist = RelationGetIndexList(relation);
 
 	*nindexes = list_length(indexoidlist);
@@ -3489,11 +3491,8 @@ vac_open_indexes(Relation relation, LOCKMODE lockmode,
 	foreach(indexoidscan, indexoidlist)
 	{
 		Oid			indexoid = lfirst_oid(indexoidscan);
-		Relation	ind;
 
-		ind = index_open(indexoid);
-		(*Irel)[i++] = ind;
-		LockRelation(ind, lockmode);
+		(*Irel)[i++] = index_open(indexoid, lockmode);
 	}
 
 	list_free(indexoidlist);
@@ -3513,9 +3512,7 @@ vac_close_indexes(int nindexes, Relation *Irel, LOCKMODE lockmode)
 	{
 		Relation	ind = Irel[nindexes];
 
-		if (lockmode != NoLock)
-			UnlockRelation(ind, lockmode);
-		index_close(ind);
+		index_close(ind, lockmode);
 	}
 	pfree(Irel);
 }
diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c
index d2727c4a470..2202e7b7e9a 100644
--- a/src/backend/commands/vacuumlazy.c
+++ b/src/backend/commands/vacuumlazy.c
@@ -31,7 +31,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.75 2006/07/14 14:52:18 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.76 2006/07/31 20:09:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -164,7 +164,7 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
 	vacrelstats->minxid = RecentXmin;
 
 	/* Open all indexes of the relation */
-	vac_open_indexes(onerel, ShareUpdateExclusiveLock, &nindexes, &Irel);
+	vac_open_indexes(onerel, RowExclusiveLock, &nindexes, &Irel);
 	hasindex = (nindexes > 0);
 
 	/* Do the vacuuming */
@@ -621,15 +621,6 @@ lazy_vacuum_index(Relation indrel,
 
 	pg_rusage_init(&ru0);
 
-	/*
-	 * Acquire appropriate type of lock on index: must be exclusive if index
-	 * AM isn't concurrent-safe.
-	 */
-	if (indrel->rd_am->amconcurrent)
-		LockRelation(indrel, RowExclusiveLock);
-	else
-		LockRelation(indrel, AccessExclusiveLock);
-
 	ivinfo.index = indrel;
 	ivinfo.vacuum_full = false;
 	ivinfo.message_level = elevel;
@@ -640,14 +631,6 @@ lazy_vacuum_index(Relation indrel,
 	*stats = index_bulk_delete(&ivinfo, *stats,
 							   lazy_tid_reaped, (void *) vacrelstats);
 
-	/*
-	 * Release lock acquired above.
-	 */
-	if (indrel->rd_am->amconcurrent)
-		UnlockRelation(indrel, RowExclusiveLock);
-	else
-		UnlockRelation(indrel, AccessExclusiveLock);
-
 	ereport(elevel,
 			(errmsg("scanned index \"%s\" to remove %d row versions",
 					RelationGetRelationName(indrel),
@@ -668,15 +651,6 @@ lazy_cleanup_index(Relation indrel,
 
 	pg_rusage_init(&ru0);
 
-	/*
-	 * Acquire appropriate type of lock on index: must be exclusive if index
-	 * AM isn't concurrent-safe.
-	 */
-	if (indrel->rd_am->amconcurrent)
-		LockRelation(indrel, RowExclusiveLock);
-	else
-		LockRelation(indrel, AccessExclusiveLock);
-
 	ivinfo.index = indrel;
 	ivinfo.vacuum_full = false;
 	ivinfo.message_level = elevel;
@@ -684,14 +658,6 @@ lazy_cleanup_index(Relation indrel,
 
 	stats = index_vacuum_cleanup(&ivinfo, stats);
 
-	/*
-	 * Release lock acquired above.
-	 */
-	if (indrel->rd_am->amconcurrent)
-		UnlockRelation(indrel, RowExclusiveLock);
-	else
-		UnlockRelation(indrel, AccessExclusiveLock);
-
 	if (!stats)
 		return;