Create a distinction between a populated matview and a scannable one.

The intent was that being populated would, long term, be just one
of the conditions which could affect whether a matview was
scannable; being populated should be necessary but not always
sufficient to scan the relation.  Since only CREATE and REFRESH
currently determine the scannability, names and comments
accidentally conflated these concepts, leading to confusion.

Also add missing locking for the SQL function which allows a
test for scannability, and fix a modularity violatiion.

Per complaints from Tom Lane, although its not clear that these
will satisfy his concerns.  Hopefully this will at least better
frame the discussion.

1 files changed, 9 insertions, 4 deletions

diff --git a/src/backend/utils/adt/dbsize.c b/src/backend/utils/adt/dbsize.c
index d589d26070d..d32d9014c7e 100644
--- a/src/backend/utils/adt/dbsize.c
+++ b/src/backend/utils/adt/dbsize.c
@@ -840,7 +840,8 @@ pg_relation_filepath(PG_FUNCTION_ARGS)
  * Indicate whether a relation is scannable.
  *
  * Currently, this is always true except for a materialized view which has not
- * been populated.
+ * been populated.  It is expected that other conditions for allowing a
+ * materialized view to be scanned will be added in later releases.
  */
 Datum
 pg_relation_is_scannable(PG_FUNCTION_ARGS)
@@ -850,9 +851,13 @@ pg_relation_is_scannable(PG_FUNCTION_ARGS)
 	bool		result;
 
 	relid = PG_GETARG_OID(0);
-	relation = RelationIdGetRelation(relid);
-	result = relation->rd_isscannable;
-	RelationClose(relation);
+	relation = try_relation_open(relid, AccessShareLock);
 
+	if (relation == NULL)
+		PG_RETURN_BOOL(false);
+
+	result = RelationIsScannable(relation);
+
+	relation_close(relation, AccessShareLock);
 	PG_RETURN_BOOL(result);
 }