From 215cfa6a869957778b5c0b8a92b3d8a46ff76fb6 Mon Sep 17 00:00:00 2001
From: Craig Ringer <craig@2ndquadrant.com>
Date: Wed, 1 Jul 2015 16:41:19 +0800
Subject: [PATCH] Permit DML on pg_catalog tables

Because many pg_catalog tables don't have a PRIMARY KEY we were
rejecting DML on them. Since pg_catalog writes don't get replicated
anyway, it's safe to permit such writes.

Fixes #102
---
 bdr_executor.c              | 13 +++++++++++++
 expected/dml/missing_pk.out | 33 +++++++++++++++++++++++++++++++++
 sql/dml/missing_pk.sql      | 18 ++++++++++++++++++
 3 files changed, 64 insertions(+)

diff --git a/bdr_executor.c b/bdr_executor.c
index 5eaae4bb8f..c5e196b5b9 100644
--- a/bdr_executor.c
+++ b/bdr_executor.c
@@ -25,6 +25,7 @@
 
 #include "catalog/indexing.h"
 #include "catalog/namespace.h"
+#include "catalog/pg_namespace.h"
 #include "catalog/pg_trigger.h"
 
 #include "commands/event_trigger.h"
@@ -956,6 +957,18 @@ BdrExecutorStart(QueryDesc *queryDesc, int eflags)
 			continue;
 		}
 
+		/*
+		 * Since changes to pg_catalog aren't replicated directly there's
+		 * no strong need to suppress direct UPDATEs on them. The usual
+		 * rule of "it's dumb to modify the catalogs directly if you don't
+		 * know what you're doing" applies.
+		 */
+		if (RelationGetNamespace(rel) == PG_CATALOG_NAMESPACE)
+		{
+			RelationClose(rel);
+			continue;
+		}
+
 		if (read_only_node)
 			ereport(ERROR,
 					(errcode(ERRCODE_READ_ONLY_SQL_TRANSACTION),
diff --git a/expected/dml/missing_pk.out b/expected/dml/missing_pk.out
index 831f82e859..332698d80c 100644
--- a/expected/dml/missing_pk.out
+++ b/expected/dml/missing_pk.out
@@ -109,6 +109,39 @@ SELECT * FROM bdr_missing_pk;
 (0 rows)
 
 \c :writedb1
+-- Direct updates to the catalogs should be permitted, though
+-- not necessarily smart.
+UPDATE pg_class
+SET relname = 'bdr_missing_pk_renamed'
+WHERE relname = 'bdr_missing_pk';
+\dt bdr_missing_pk*
+                List of relations
+ Schema |          Name          | Type  | Owner 
+--------+------------------------+-------+-------
+ public | bdr_missing_pk_parent  | table | craig
+ public | bdr_missing_pk_renamed | table | craig
+(2 rows)
+
+SELECT pg_xlog_wait_remote_apply(pg_current_xlog_location(), 0);
+ pg_xlog_wait_remote_apply 
+---------------------------
+ 
+(1 row)
+
+\c :readdb2
+-- The catalog change should not replicate
+\dt bdr_missing_pk*
+               List of relations
+ Schema |         Name          | Type  | Owner 
+--------+-----------------------+-------+-------
+ public | bdr_missing_pk        | table | craig
+ public | bdr_missing_pk_parent | table | craig
+(2 rows)
+
+\c :writedb1
+UPDATE pg_class
+SET relname = 'bdr_missing_pk'
+WHERE relname = 'bdr_missing_pk_renamed';
 BEGIN;
 SET LOCAL bdr.permit_ddl_locking = true;
 SELECT bdr.bdr_replicate_ddl_command($$DROP TABLE public.bdr_missing_pk CASCADE;$$);
diff --git a/sql/dml/missing_pk.sql b/sql/dml/missing_pk.sql
index 63df87683a..03a05ad62b 100644
--- a/sql/dml/missing_pk.sql
+++ b/sql/dml/missing_pk.sql
@@ -61,6 +61,24 @@ SELECT pg_xlog_wait_remote_apply(pg_current_xlog_location(), 0);
 SELECT * FROM bdr_missing_pk;
 
 \c :writedb1
+-- Direct updates to the catalogs should be permitted, though
+-- not necessarily smart.
+UPDATE pg_class
+SET relname = 'bdr_missing_pk_renamed'
+WHERE relname = 'bdr_missing_pk';
+
+\dt bdr_missing_pk*
+SELECT pg_xlog_wait_remote_apply(pg_current_xlog_location(), 0);
+
+\c :readdb2
+-- The catalog change should not replicate
+\dt bdr_missing_pk*
+
+\c :writedb1
+UPDATE pg_class
+SET relname = 'bdr_missing_pk'
+WHERE relname = 'bdr_missing_pk_renamed';
+
 BEGIN;
 SET LOCAL bdr.permit_ddl_locking = true;
 SELECT bdr.bdr_replicate_ddl_command($$DROP TABLE public.bdr_missing_pk CASCADE;$$);
-- 
2.39.5