Make concurrent refresh check early that there is a unique index on matview. (#10215)

In REFRESH MATERIALIZED VIEW command, CONCURRENTLY option is only
allowed if there is at least one unique index with no WHERE clause on
one or more columns of the matview. Previously, concurrent refresh
checked the existence of a unique index on the matview after filling
the data to new snapshot, i.e., after calling refresh_matview_datafill().
So, when there was no unique index, we could need to wait a long time
before we detected that and got the error. It was a waste of time.

To eliminate such wasting time, this commit changes concurrent refresh
so that it checks the existence of a unique index at the beginning of
the refresh operation, i.e., before starting any time-consuming jobs.
If CONCURRENTLY option is not allowed due to lack of a unique index,
concurrent refresh can immediately detect it and emit an error.

Author: Masahiko Sawada
Reviewed-by: Michael Paquier, Fujii Masao
Co-authored-by: NFujii Masao <fujii@postgresql.org>

src/backend/commands/matview.c

@@ -238,6 +238,50 @@ ExecRefreshMatView(RefreshMatViewStmt *stmt, const char *queryString,
 			 "the rule for materialized view \"%s\" is not a single action",
 			 RelationGetRelationName(matviewRel));
 
+	/*
+	 * Check that there is a unique index with no WHERE clause on
+	 * one or more columns of the materialized view if CONCURRENTLY
+	 * is specified.
+	 */
+	if (concurrent)
+	{
+		List		*indexoidlist = RelationGetIndexList(matviewRel);
+		ListCell 	*indexoidscan;
+		bool		hasUniqueIndex = false;
+
+		foreach(indexoidscan, indexoidlist)
+		{
+			Oid			indexoid = lfirst_oid(indexoidscan);
+			Relation	indexRel;
+			Form_pg_index	indexStruct;
+
+			indexRel = index_open(indexoid, AccessShareLock);
+			indexStruct = indexRel->rd_index;
+
+			if (indexStruct->indisunique &&
+				IndexIsValid(indexStruct) &&
+				RelationGetIndexExpressions(indexRel) == NIL &&
+				RelationGetIndexPredicate(indexRel) == NIL &&
+				indexStruct->indnatts > 0)
+			{
+				hasUniqueIndex = true;
+				index_close(indexRel, AccessShareLock);
+				break;
+			}
+
+			index_close(indexRel, AccessShareLock);
+		}
+
+		list_free(indexoidlist);
+
+		if (!hasUniqueIndex)
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg("cannot refresh materialized view \"%s\" concurrently",
+							quote_qualified_identifier(get_namespace_name(RelationGetNamespace(matviewRel)),
+													   RelationGetRelationName(matviewRel))),
+					 errhint("Create a unique index with no WHERE clause on one or more columns of the materialized view.")));
+	}
 
 	/*
 	 * Check for active uses of the relation in the current transaction, such
@@ -855,12 +899,14 @@ refresh_by_match_merge(Oid matviewOid, Oid tempOid, Oid relowner,
 
 	list_free(indexoidlist);
 
-	if (!foundUniqueIndex)
-		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-			   errmsg("cannot refresh materialized view \"%s\" concurrently",
-					  matviewname),
-				 errhint("Create a unique index with no WHERE clause on one or more columns of the materialized view.")));
+	/*
+	 * There must be at least one unique index on the matview.
+	 *
+	 * ExecRefreshMatView() checks that after taking the exclusive lock on
+	 * the matview. So at least one unique index is guaranteed to exist here
+	 * because the lock is still being held.
+	 */
+	Assert(foundUniqueIndex);