Add comments warning against generalizing default_with_oids.

pg_dump has historically assumed that default_with_oids affects only plain
tables and not other relkinds.  Conceivably we could make it apply to some
newly invented relkind if we did so from the get-go, but changing the
behavior for existing object types will break existing dump scripts.
Add code comments warning about this interaction.

Also, make sure that default_with_oids doesn't cause parse_utilcmd.c to
think that CREATE FOREIGN TABLE will create an OID column.  I think this is
only a latent bug right now, since we don't allow UNIQUE/PKEY constraints
in CREATE FOREIGN TABLE, but it's better to be consistent and future-proof.

1 files changed, 8 insertions, 0 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 06e4332d2ac..bedd8aeb782 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -579,6 +579,14 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId,
 	 */
 	descriptor = BuildDescForRelation(schema);
 
+	/*
+	 * Notice that we allow OIDs here only for plain tables, even though some
+	 * other relkinds can support them.  This is necessary because the
+	 * default_with_oids GUC must apply only to plain tables and not any other
+	 * relkind; doing otherwise would break existing pg_dump files.  We could
+	 * allow explicit "WITH OIDS" while not allowing default_with_oids to
+	 * affect other relkinds, but it would complicate interpretOidsOption().
+	 */
 	localHasOids = interpretOidsOption(stmt->options,
 									   (relkind == RELKIND_RELATION));
 	descriptor->tdhasoid = (localHasOids || parentOidCount > 0);