Generalize TRUNCATE to support truncating multiple tables in one

command.  This is useful because we can allow truncation of tables
referenced by foreign keys, so long as the referencing table is
truncated in the same command.

Alvaro Herrera

1 files changed, 95 insertions, 65 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 89dd8dffae0..6abf4ab65e1 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 1.143 2005/01/24 23:21:57 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.144 2005/01/27 03:17:30 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -525,88 +525,113 @@ RemoveRelation(const RangeVar *relation, DropBehavior behavior)
 }
 
 /*
- * TruncateRelation
- *		Removes all the rows from a relation.
+ * ExecuteTruncate
+ * 		Executes a TRUNCATE command.
+ *
+ * This is a multi-relation truncate.  It first opens and grabs exclusive
+ * locks on all relations involved, checking permissions and otherwise
+ * verifying that the relation is OK for truncation.  When they are all
+ * open, it checks foreign key references on them, namely that FK references
+ * are all internal to the group that's being truncated.  Finally all
+ * relations are truncated and reindexed.
  */
 void
-TruncateRelation(const RangeVar *relation)
+ExecuteTruncate(List *relations)
 {
-	Relation	rel;
-	Oid			heap_relid;
-	Oid			toast_relid;
+	List		*rels = NIL;
+	ListCell	*cell;
 
-	/* Grab exclusive lock in preparation for truncate */
-	rel = heap_openrv(relation, AccessExclusiveLock);
+	foreach(cell, relations)
+	{
+		RangeVar   *rv = lfirst(cell);
+		Relation	rel;
 
-	/* Only allow truncate on regular tables */
-	if (rel->rd_rel->relkind != RELKIND_RELATION)
-		ereport(ERROR,
-				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("\"%s\" is not a table",
-						RelationGetRelationName(rel))));
+		/* Grab exclusive lock in preparation for truncate */
+		rel = heap_openrv(rv, AccessExclusiveLock);
 
-	/* Permissions checks */
-	if (!pg_class_ownercheck(RelationGetRelid(rel), GetUserId()))
-		aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
-					   RelationGetRelationName(rel));
+		/* Only allow truncate on regular tables */
+		if (rel->rd_rel->relkind != RELKIND_RELATION)
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					 errmsg("\"%s\" is not a table",
+						 RelationGetRelationName(rel))));
 
-	if (!allowSystemTableMods && IsSystemRelation(rel))
-		ereport(ERROR,
-				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
-				 errmsg("permission denied: \"%s\" is a system catalog",
-						RelationGetRelationName(rel))));
+		/* Permissions checks */
+		if (!pg_class_ownercheck(RelationGetRelid(rel), GetUserId()))
+			aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
+					RelationGetRelationName(rel));
 
-	/*
-	 * We can never allow truncation of shared or nailed-in-cache
-	 * relations, because we can't support changing their relfilenode
-	 * values.
-	 */
-	if (rel->rd_rel->relisshared || rel->rd_isnailed)
-		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("cannot truncate system relation \"%s\"",
-						RelationGetRelationName(rel))));
+		if (!allowSystemTableMods && IsSystemRelation(rel))
+			ereport(ERROR,
+					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+					 errmsg("permission denied: \"%s\" is a system catalog",
+						 RelationGetRelationName(rel))));
 
-	/*
-	 * Don't allow truncate on temp tables of other backends ... their
-	 * local buffer manager is not going to cope.
-	 */
-	if (isOtherTempNamespace(RelationGetNamespace(rel)))
-		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-		  errmsg("cannot truncate temporary tables of other sessions")));
+		/*
+		 * We can never allow truncation of shared or nailed-in-cache
+		 * relations, because we can't support changing their relfilenode
+		 * values.
+		 */
+		if (rel->rd_rel->relisshared || rel->rd_isnailed)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("cannot truncate system relation \"%s\"",
+						 RelationGetRelationName(rel))));
 
-	/*
-	 * Don't allow truncate on tables which are referenced by foreign keys
-	 */
-	heap_truncate_check_FKs(rel);
+		/*
+		 * Don't allow truncate on temp tables of other backends ... their
+		 * local buffer manager is not going to cope.
+		 */
+		if (isOtherTempNamespace(RelationGetNamespace(rel)))
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("cannot truncate temporary tables of other sessions")));
+
+		/* Save it into the list of rels to truncate */
+		rels = lappend(rels, rel);
+	}
 
 	/*
-	 * Okay, here we go: create a new empty storage file for the relation,
-	 * and assign it as the relfilenode value.	The old storage file is
-	 * scheduled for deletion at commit.
+	 * Check foreign key references.
 	 */
-	setNewRelfilenode(rel);
-
-	heap_relid = RelationGetRelid(rel);
-	toast_relid = rel->rd_rel->reltoastrelid;
-
-	heap_close(rel, NoLock);
+	heap_truncate_check_FKs(rels, false);
 
 	/*
-	 * The same for the toast table, if any.
+	 * OK, truncate each table.
 	 */
-	if (OidIsValid(toast_relid))
+	foreach(cell, rels)
 	{
-		rel = relation_open(toast_relid, AccessExclusiveLock);
+		Relation	rel = lfirst(cell);
+		Oid			heap_relid;
+		Oid			toast_relid;
+
+		/*
+		 * Create a new empty storage file for the relation, and assign it as
+		 * the relfilenode value.	The old storage file is scheduled for
+		 * deletion at commit.
+		 */
 		setNewRelfilenode(rel);
+
+		heap_relid = RelationGetRelid(rel);
+		toast_relid = rel->rd_rel->reltoastrelid;
+
 		heap_close(rel, NoLock);
-	}
 
-	/*
-	 * Reconstruct the indexes to match, and we're done.
-	 */
-	reindex_relation(heap_relid, true);
+		/*
+		 * The same for the toast table, if any.
+		 */
+		if (OidIsValid(toast_relid))
+		{
+			rel = relation_open(toast_relid, AccessExclusiveLock);
+			setNewRelfilenode(rel);
+			heap_close(rel, NoLock);
+		}
+
+		/*
+		 * Reconstruct the indexes to match, and we're done.
+		 */
+		reindex_relation(heap_relid, true);
+	}
 }
 
 /*----------
@@ -6013,6 +6038,7 @@ void
 PreCommit_on_commit_actions(void)
 {
 	ListCell   *l;
+	List	   *oids_to_truncate = NIL;
 
 	foreach(l, on_commits)
 	{
@@ -6029,8 +6055,7 @@ PreCommit_on_commit_actions(void)
 				/* Do nothing (there shouldn't be such entries, actually) */
 				break;
 			case ONCOMMIT_DELETE_ROWS:
-				heap_truncate(oc->relid);
-				CommandCounterIncrement();		/* XXX needed? */
+				oids_to_truncate = lappend_oid(oids_to_truncate, oc->relid);
 				break;
 			case ONCOMMIT_DROP:
 				{
@@ -6051,6 +6076,11 @@ PreCommit_on_commit_actions(void)
 				}
 		}
 	}
+	if (oids_to_truncate != NIL)
+	{
+		heap_truncate(oids_to_truncate);
+		CommandCounterIncrement();				/* XXX needed? */
+	}
 }
 
 /*