Allow a partdesc-omitting-partitions to be cached

Makes partition descriptor acquisition faster during the transient
period in which a partition is in the process of being detached.

This also adds the restriction that only one partition can be in
pending-detach state for a partitioned table.

While at it, return find_inheritance_children() API to what it was
before 71f4c8c6f74b, and create a separate
find_inheritance_children_extended() that returns detailed info about
detached partitions.

(This incidentally fixes a bug in 8aba9322511 whereby a memory context
holding a transient partdesc is reparented to a NULL PortalContext,
leading to permanent leak of that memory.  The fix is to no longer rely
on reparenting contexts to PortalContext.   Reported by Amit Langote.)

Per gripe from Amit Langote
Discussion: https://postgr.es/m/CA+HiwqFgpP1LxJZOBYGt9rpvTjXXkg5qG2+Xch2Z1Q7KrqZR1A@mail.gmail.com

1 files changed, 39 insertions, 27 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 8e717ada28d..d9ba87a2a3a 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -3492,7 +3492,7 @@ renameatt_internal(Oid myrelid,
 		 * expected_parents will only be 0 if we are not already recursing.
 		 */
 		if (expected_parents == 0 &&
-			find_inheritance_children(myrelid, true, NoLock, NULL) != NIL)
+			find_inheritance_children(myrelid, NoLock) != NIL)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 					 errmsg("inherited column \"%s\" must be renamed in child tables too",
@@ -3691,7 +3691,7 @@ rename_constraint_internal(Oid myrelid,
 		else
 		{
 			if (expected_parents == 0 &&
-				find_inheritance_children(myrelid, true, NoLock, NULL) != NIL)
+				find_inheritance_children(myrelid, NoLock) != NIL)
 				ereport(ERROR,
 						(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 						 errmsg("inherited constraint \"%s\" must be renamed in child tables too",
@@ -6565,7 +6565,7 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	 */
 	if (colDef->identity &&
 		recurse &&
-		find_inheritance_children(myrelid, true, NoLock, NULL) != NIL)
+		find_inheritance_children(myrelid, NoLock) != NIL)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 				 errmsg("cannot recursively add identity column to table that has child tables")));
@@ -6811,7 +6811,7 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	 * use find_all_inheritors to do it in one pass.
 	 */
 	children =
-		find_inheritance_children(RelationGetRelid(rel), true, lockmode, NULL);
+		find_inheritance_children(RelationGetRelid(rel), lockmode);
 
 	/*
 	 * If we are told not to recurse, there had better not be any child
@@ -7674,7 +7674,7 @@ ATPrepDropExpression(Relation rel, AlterTableCmd *cmd, bool recurse, bool recurs
 	 * resulting state can be properly dumped and restored.
 	 */
 	if (!recurse &&
-		find_inheritance_children(RelationGetRelid(rel), true, lockmode, NULL))
+		find_inheritance_children(RelationGetRelid(rel), lockmode))
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("ALTER TABLE / DROP EXPRESSION must be applied to child tables too")));
@@ -8282,7 +8282,7 @@ ATExecDropColumn(List **wqueue, Relation rel, const char *colName,
 	 * use find_all_inheritors to do it in one pass.
 	 */
 	children =
-		find_inheritance_children(RelationGetRelid(rel), true, lockmode, NULL);
+		find_inheritance_children(RelationGetRelid(rel), lockmode);
 
 	if (children)
 	{
@@ -8770,7 +8770,7 @@ ATAddCheckConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	 * use find_all_inheritors to do it in one pass.
 	 */
 	children =
-		find_inheritance_children(RelationGetRelid(rel), true, lockmode, NULL);
+		find_inheritance_children(RelationGetRelid(rel), lockmode);
 
 	/*
 	 * Check if ONLY was specified with ALTER TABLE.  If so, allow the
@@ -11303,8 +11303,7 @@ ATExecDropConstraint(Relation rel, const char *constrName,
 	 * use find_all_inheritors to do it in one pass.
 	 */
 	if (!is_no_inherit_constraint)
-		children = find_inheritance_children(RelationGetRelid(rel), true,
-											 lockmode, NULL);
+		children = find_inheritance_children(RelationGetRelid(rel), lockmode);
 	else
 		children = NIL;
 
@@ -11688,8 +11687,7 @@ ATPrepAlterColumnType(List **wqueue,
 		}
 	}
 	else if (!recursing &&
-			 find_inheritance_children(RelationGetRelid(rel), true,
-									   NoLock, NULL) != NIL)
+			 find_inheritance_children(RelationGetRelid(rel), NoLock) != NIL)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
 				 errmsg("type of inherited column \"%s\" must be changed in child tables too",
@@ -14601,7 +14599,8 @@ ATExecDropInherit(Relation rel, RangeVar *parent, LOCKMODE lockmode)
  * MarkInheritDetached
  *
  * Set inhdetachpending for a partition, for ATExecDetachPartition
- * in concurrent mode.
+ * in concurrent mode.  While at it, verify that no other partition is
+ * already pending detach.
  */
 static void
 MarkInheritDetached(Relation child_rel, Relation parent_rel)
@@ -14617,32 +14616,45 @@ MarkInheritDetached(Relation child_rel, Relation parent_rel)
 	Assert(parent_rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE);
 
 	/*
-	 * Find pg_inherits entries by inhrelid.
+	 * Find pg_inherits entries by inhparent.  (We need to scan them all in
+	 * order to verify that no other partition is pending detach.)
 	 */
 	catalogRelation = table_open(InheritsRelationId, RowExclusiveLock);
 	ScanKeyInit(&key,
-				Anum_pg_inherits_inhrelid,
+				Anum_pg_inherits_inhparent,
 				BTEqualStrategyNumber, F_OIDEQ,
-				ObjectIdGetDatum(RelationGetRelid(child_rel)));
-	scan = systable_beginscan(catalogRelation, InheritsRelidSeqnoIndexId,
+				ObjectIdGetDatum(RelationGetRelid(parent_rel)));
+	scan = systable_beginscan(catalogRelation, InheritsParentIndexId,
 							  true, NULL, 1, &key);
 
 	while (HeapTupleIsValid(inheritsTuple = systable_getnext(scan)))
 	{
-		HeapTuple	newtup;
+		Form_pg_inherits inhForm;
 
-		if (((Form_pg_inherits) GETSTRUCT(inheritsTuple))->inhparent !=
-			RelationGetRelid(parent_rel))
-			elog(ERROR, "bad parent tuple found for partition %u",
-				 RelationGetRelid(child_rel));
+		inhForm = (Form_pg_inherits) GETSTRUCT(inheritsTuple);
+		if (inhForm->inhdetachpending)
+			ereport(ERROR,
+					errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					errmsg("partition \"%s\" already pending detach in partitioned table \"%s.%s\"",
+						   get_rel_name(inhForm->inhrelid),
+						   get_namespace_name(parent_rel->rd_rel->relnamespace),
+						   RelationGetRelationName(parent_rel)),
+					errhint("Use ALTER TABLE ... DETACH PARTITION ... FINALIZE to complete the detach operation."));
+
+		if (inhForm->inhrelid == RelationGetRelid(child_rel))
+		{
+			HeapTuple	newtup;
 
-		newtup = heap_copytuple(inheritsTuple);
-		((Form_pg_inherits) GETSTRUCT(newtup))->inhdetachpending = true;
+			newtup = heap_copytuple(inheritsTuple);
+			((Form_pg_inherits) GETSTRUCT(newtup))->inhdetachpending = true;
 
-		CatalogTupleUpdate(catalogRelation,
-						   &inheritsTuple->t_self,
-						   newtup);
-		found = true;
+			CatalogTupleUpdate(catalogRelation,
+							   &inheritsTuple->t_self,
+							   newtup);
+			found = true;
+			heap_freetuple(newtup);
+			/* keep looking, to ensure we catch others pending detach */
+		}
 	}
 
 	/* Done */