Register a relcache callback to invalidate cached Oids when necessary.

Author: danolivo

expected/lolor.out

@@ -54,10 +54,17 @@ REINDEX INDEX CONCURRENTLY lolor.pg_largeobject_pkey;
 REINDEX INDEX CONCURRENTLY lolor.pg_largeobject_metadata_pkey;
 BEGIN;
 SELECT lo_open(:loid, 262144) AS fd \gset
-ERROR:  could not open relation with OID 16399
 SELECT convert_from(loread(:fd, 1024), 'UTF8');
-ERROR:  current transaction is aborted, commands ignored until end of transaction block
+     convert_from     
+----------------------
+ Example large object
+(1 row)
+
 SELECT lo_close(:fd);
-ERROR:  current transaction is aborted, commands ignored until end of transaction block
+ lo_close 
+----------
+        0
+(1 row)
+
 END;
 DROP EXTENSION lolor;

src/lolor.c

@@ -24,6 +24,7 @@
 #include "nodes/value.h"
 #include "nodes/print.h"
 #include "utils/builtins.h"
+#include "utils/inval.h"
 #include "utils/guc.h"
 #include "utils/rel.h"
 #include "utils/lsyscache.h"
@@ -131,6 +132,18 @@ lolor_subxact_callback(SubXactEvent event, SubTransactionId mySubid,
 	}
 }
 
+/*
+ * For the sake of performance, make it simple
+ */
+static void
+relcache_invalidate_callback(Datum arg, Oid reloid)
+{
+	LOLOR_LargeObjectRelationId = InvalidOid;
+	LOLOR_LargeObjectLOidPNIndexId = InvalidOid;
+	LOLOR_LargeObjectMetadataRelationId = InvalidOid;
+	LOLOR_LargeObjectMetadataOidIndexId = InvalidOid;
+}
+
 /*
  * Entry point for this module.
  */
@@ -151,6 +164,12 @@ _PG_init(void)
 	/* register transaction callbacks for cleanup. */
 	RegisterXactCallback(lolor_xact_callback, NULL);
 	RegisterSubXactCallback(lolor_subxact_callback, NULL);
+
+	/*
+	 * Something may change object ID accidentially (REINDEX is a good example).
+	 * So, it is necessary to invalidate cache of Oids.
+	 */
+	CacheRegisterRelcacheCallback(relcache_invalidate_callback, (Datum) 0);
 }
 
 /*