Back-patch the 8.3 fix that prohibits TRUNCATE, CLUSTER, and REINDEX when the

current transaction has any open references to the target relation or index
(implying it has an active query using the relation).  Also back-patch the
8.2 fix that prohibits TRUNCATE and CLUSTER when there are pending
AFTER-trigger events.  Per suggestion from Heikki.

1 files changed, 62 insertions, 46 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index a9a13a803e5..3006f0a3627 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 1.206.2.5 2008/05/09 22:37:41 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.206.2.6 2008/05/27 21:13:25 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -597,13 +597,6 @@ ExecuteTruncate(TruncateStmt *stmt)
 #endif
 
 	/*
-	 * Also check for pending AFTER trigger events on the target relations. We
-	 * can't just leave those be, since they will try to fetch tuples that the
-	 * TRUNCATE removes.
-	 */
-	AfterTriggerCheckTruncate(relids);
-
-	/*
 	 * OK, truncate each table.
 	 */
 	foreach(cell, rels)
@@ -683,6 +676,12 @@ truncate_check_rel(Relation rel)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 			  errmsg("cannot truncate temporary tables of other sessions")));
+
+	/*
+	 * Also check for active uses of the relation in the current transaction,
+	 * including open scans and pending AFTER trigger events.
+	 */
+	CheckTableNotInUse(rel, "TRUNCATE");
 }
 
 /*----------
@@ -1913,6 +1912,55 @@ update_ri_trigger_args(Oid relid,
 }
 
 /*
+ * Disallow ALTER TABLE (and similar commands) when the current backend has
+ * any open reference to the target table besides the one just acquired by
+ * the calling command; this implies there's an open cursor or active plan.
+ * We need this check because our AccessExclusiveLock doesn't protect us
+ * against stomping on our own foot, only other people's feet!
+ *
+ * For ALTER TABLE, the only case known to cause serious trouble is ALTER
+ * COLUMN TYPE, and some changes are obviously pretty benign, so this could
+ * possibly be relaxed to only error out for certain types of alterations.
+ * But the use-case for allowing any of these things is not obvious, so we
+ * won't work hard at it for now.
+ *
+ * We also reject these commands if there are any pending AFTER trigger events
+ * for the rel.  This is certainly necessary for the rewriting variants of
+ * ALTER TABLE, because they don't preserve tuple TIDs and so the pending
+ * events would try to fetch the wrong tuples.  It might be overly cautious
+ * in other cases, but again it seems better to err on the side of paranoia.
+ *
+ * REINDEX calls this with "rel" referencing the index to be rebuilt; here
+ * we are worried about active indexscans on the index.  The trigger-event
+ * check can be skipped, since we are doing no damage to the parent table.
+ *
+ * The statement name (eg, "ALTER TABLE") is passed for use in error messages.
+ */
+void
+CheckTableNotInUse(Relation rel, const char *stmt)
+{
+	int			expected_refcnt;
+
+	expected_refcnt = rel->rd_isnailed ? 2 : 1;
+	if (rel->rd_refcnt != expected_refcnt)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_IN_USE),
+				 /* translator: first %s is a SQL command, eg ALTER TABLE */
+				 errmsg("cannot %s \"%s\" because "
+						"it is being used by active queries in this session",
+						stmt, RelationGetRelationName(rel))));
+
+	if (rel->rd_rel->relkind != RELKIND_INDEX &&
+		AfterTriggerPendingOnRel(RelationGetRelid(rel)))
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_IN_USE),
+				 /* translator: first %s is a SQL command, eg ALTER TABLE */
+				 errmsg("cannot %s \"%s\" because "
+						"it has pending trigger events",
+						stmt, RelationGetRelationName(rel))));
+}
+
+/*
  * AlterTable
  *		Execute ALTER TABLE, which can be a list of subcommands
  *
@@ -1949,26 +1997,8 @@ void
 AlterTable(AlterTableStmt *stmt)
 {
 	Relation rel = relation_openrv(stmt->relation, AccessExclusiveLock);
-	int			expected_refcnt;
 
-	/*
-	 * Disallow ALTER TABLE when the current backend has any open reference
-	 * to it besides the one we just got (such as an open cursor or active
-	 * plan); our AccessExclusiveLock doesn't protect us against stomping on
-	 * our own foot, only other people's feet!
-	 *
-	 * Note: the only case known to cause serious trouble is ALTER COLUMN TYPE,
-	 * and some changes are obviously pretty benign, so this could possibly
-	 * be relaxed to only error out for certain types of alterations.  But
-	 * the use-case for allowing any of these things is not obvious, so we
-	 * won't work hard at it for now.
-	 */
-	expected_refcnt = rel->rd_isnailed ? 2 : 1;
-	if (rel->rd_refcnt != expected_refcnt)
-		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_IN_USE),
-				 errmsg("relation \"%s\" is being used by active queries in this session",
-						RelationGetRelationName(rel))));
+	CheckTableNotInUse(rel, "ALTER TABLE");
 
 	ATController(rel, stmt->cmds, interpretInhOption(stmt->relation->inhOpt));
 }
@@ -1981,7 +2011,8 @@ AlterTable(AlterTableStmt *stmt)
  * We do not reject if the relation is already open, because it's quite
  * likely that one or more layers of caller have it open.  That means it
  * is unsafe to use this entry point for alterations that could break
- * existing query plans.
+ * existing query plans.  On the assumption it's not used for such, we
+ * don't have to reject pending AFTER triggers, either.
  */
 void
 AlterTableInternal(Oid relid, List *cmds, bool recurse)
@@ -2939,12 +2970,7 @@ ATSimpleRecursion(List **wqueue, Relation rel,
 			if (childrelid == relid)
 				continue;
 			childrel = relation_open(childrelid, AccessExclusiveLock);
-			/* check for child relation in use in this session */
-			if (childrel->rd_refcnt != 1)
-				ereport(ERROR,
-						(errcode(ERRCODE_OBJECT_IN_USE),
-						 errmsg("relation \"%s\" is being used by active queries in this session",
-								RelationGetRelationName(childrel))));
+			CheckTableNotInUse(childrel, "ALTER TABLE");
 			ATPrepCmd(wqueue, childrel, cmd, false, true);
 			relation_close(childrel, NoLock);
 		}
@@ -2976,12 +3002,7 @@ ATOneLevelRecursion(List **wqueue, Relation rel,
 		Relation	childrel;
 
 		childrel = relation_open(childrelid, AccessExclusiveLock);
-		/* check for child relation in use in this session */
-		if (childrel->rd_refcnt != 1)
-			ereport(ERROR,
-					(errcode(ERRCODE_OBJECT_IN_USE),
-					 errmsg("relation \"%s\" is being used by active queries in this session",
-							RelationGetRelationName(childrel))));
+		CheckTableNotInUse(childrel, "ALTER TABLE");
 		ATPrepCmd(wqueue, childrel, cmd, true, true);
 		relation_close(childrel, NoLock);
 	}
@@ -3799,12 +3820,7 @@ ATExecDropColumn(Relation rel, const char *colName,
 			Form_pg_attribute childatt;
 
 			childrel = heap_open(childrelid, AccessExclusiveLock);
-			/* check for child relation in use in this session */
-			if (childrel->rd_refcnt != 1)
-				ereport(ERROR,
-						(errcode(ERRCODE_OBJECT_IN_USE),
-						 errmsg("relation \"%s\" is being used by active queries in this session",
-								RelationGetRelationName(childrel))));
+			CheckTableNotInUse(childrel, "ALTER TABLE");
 
 			tuple = SearchSysCacheCopyAttName(childrelid, colName);
 			if (!HeapTupleIsValid(tuple))		/* shouldn't happen */