Allow TRUNCATE on base tables (#144)

When a base table is truncated, the view content will be empty if the
view definition query does not contain an aggregate without a GROUP clause.
Therefore, such views can be truncated.

Aggregate views without a GROUP clause always have one row. Therefore,
if a base table is truncated, the view will not be empty and will contain
a row with NULL value (or 0 for count()). So, in this case, we refresh the
view instead of truncating it.

createas.c

@@ -509,9 +509,11 @@ CreateIvmTriggersOnBaseTablesRecurse(Query *qry, Node *node, Oid matviewOid,
 					CreateIvmTrigger(rte->relid, matviewOid, TRIGGER_TYPE_INSERT, TRIGGER_TYPE_BEFORE, ex_lock);
 					CreateIvmTrigger(rte->relid, matviewOid, TRIGGER_TYPE_DELETE, TRIGGER_TYPE_BEFORE, ex_lock);
 					CreateIvmTrigger(rte->relid, matviewOid, TRIGGER_TYPE_UPDATE, TRIGGER_TYPE_BEFORE, ex_lock);
+					CreateIvmTrigger(rte->relid, matviewOid, TRIGGER_TYPE_TRUNCATE, TRIGGER_TYPE_BEFORE, true);
 					CreateIvmTrigger(rte->relid, matviewOid, TRIGGER_TYPE_INSERT, TRIGGER_TYPE_AFTER, ex_lock);
 					CreateIvmTrigger(rte->relid, matviewOid, TRIGGER_TYPE_DELETE, TRIGGER_TYPE_AFTER, ex_lock);
 					CreateIvmTrigger(rte->relid, matviewOid, TRIGGER_TYPE_UPDATE, TRIGGER_TYPE_AFTER, ex_lock);
+					CreateIvmTrigger(rte->relid, matviewOid, TRIGGER_TYPE_TRUNCATE, TRIGGER_TYPE_AFTER, true);
 
 					*relids = bms_add_member(*relids, rte->relid);
 				}
@@ -577,6 +579,9 @@ CreateIvmTrigger(Oid relOid, Oid viewOid, int16 type, int16 timing, bool ex_lock
 		case TRIGGER_TYPE_UPDATE:
 			ivm_trigger->trigname = (timing == TRIGGER_TYPE_BEFORE ? "IVM_trigger_upd_before" : "IVM_trigger_upd_after");
 			break;
+		case TRIGGER_TYPE_TRUNCATE:
+			ivm_trigger->trigname = (timing == TRIGGER_TYPE_BEFORE ? "IVM_trigger_truncate_before" : "IVM_trigger_truncate_after");
+			break;
 		default:
 			elog(ERROR, "unsupported trigger type");
 	}

expected/pg_ivm.out

@@ -77,6 +77,23 @@ SELECT * FROM mv_ivm_1 ORDER BY 1,2,3;
  4 | 40 | 104
 (4 rows)
 
+-- TRUNCATE a base table in join views
+BEGIN;
+TRUNCATE mv_base_a;
+SELECT * FROM mv_ivm_1;
+ i | j | k 
+---+---+---
+(0 rows)
+
+ROLLBACK;
+BEGIN;
+TRUNCATE mv_base_b;
+SELECT * FROM mv_ivm_1;
+ i | j | k 
+---+---+---
+(0 rows)
+
+ROLLBACK;
 -- some query syntax
 BEGIN;
 CREATE FUNCTION ivm_func() RETURNS int LANGUAGE 'sql'
@@ -245,6 +262,27 @@ SELECT * FROM mv_ivm_agg ORDER BY 1,2,3;
  5 |  50 |     1 |                 1 |             1
 (5 rows)
 
+ROLLBACK;
+-- TRUNCATE a base table in aggregate views
+BEGIN;
+SELECT create_immv('mv_ivm_agg', 'SELECT i, SUM(j), COUNT(*) FROM mv_base_a GROUP BY i');
+NOTICE:  created index "mv_ivm_agg_index" on immv "mv_ivm_agg"
+ create_immv 
+-------------
+           5
+(1 row)
+
+TRUNCATE mv_base_a;
+SELECT sum, count FROM mv_ivm_agg;
+ sum | count 
+-----+-------
+(0 rows)
+
+SELECT i, SUM(j), COUNT(*) FROM mv_base_a GROUP BY i;
+ i | sum | count 
+---+-----+-------
+(0 rows)
+
 ROLLBACK;
 -- support aggregate functions without GROUP clause
 BEGIN;
@@ -277,6 +315,31 @@ SELECT * FROM mv_ivm_group ORDER BY 1;
      |     0 |     |                 0 |                 0 |                 |             0
 (1 row)
 
+ROLLBACK;
+-- TRUNCATE a base table in aggregate views without GROUP clause
+BEGIN;
+SELECT create_immv('mv_ivm_group', 'SELECT SUM(j), COUNT(j), AVG(j) FROM mv_base_a');
+NOTICE:  could not create an index on immv "mv_ivm_group" automatically
+DETAIL:  This target list does not have all the primary key columns, or this view does not contain GROUP BY or DISTINCT clause.
+HINT:  Create an index on the immv for efficient incremental maintenance.
+ create_immv 
+-------------
+           1
+(1 row)
+
+TRUNCATE mv_base_a;
+SELECT sum, count, avg FROM mv_ivm_group;
+ sum | count | avg 
+-----+-------+-----
+     |     0 |    
+(1 row)
+
+SELECT SUM(j), COUNT(j), AVG(j) FROM mv_base_a;
+ sum | count | avg 
+-----+-------+-----
+     |     0 |    
+(1 row)
+
 ROLLBACK;
 -- resolved issue: When use AVG() function and values is indivisible, result of AVG() is incorrect.
 BEGIN;

matview.c

@@ -816,9 +816,6 @@ IVM_immediate_maintenance(PG_FUNCTION_ARGS)
 
 	matviewRel = table_open(matviewOid, NoLock);
 
-	/* get view query*/
-	query = get_immv_query(matviewRel);
-
 	/* Make sure IMMV is a table. */
 	Assert(matviewRel->rd_rel->relkind == RELKIND_RELATION);
 
@@ -848,6 +845,72 @@ IVM_immediate_maintenance(PG_FUNCTION_ARGS)
 						   save_sec_context | SECURITY_RESTRICTED_OPERATION);
 	save_nestlevel = NewGUCNestLevel();
 
+	/* get view query*/
+	query = get_immv_query(matviewRel);
+
+	/*
+	 * When a base table is truncated, the view content will be empty if the
+	 * view definition query does not contain an aggregate without a GROUP clause.
+	 * Therefore, such views can be truncated.
+	 *
+	 * Aggregate views without a GROUP clause always have one row. Therefore,
+	 * if a base table is truncated, the view will not be empty and will contain
+	 * a row with NULL value (or 0 for count()). So, in this case, we refresh the
+	 * view instead of truncating it.
+	 */
+	if (TRIGGER_FIRED_BY_TRUNCATE(trigdata->tg_event))
+	{
+		if (!(query->hasAggs && query->groupClause == NIL))
+		{
+			OpenImmvIncrementalMaintenance();
+			ExecuteTruncateGuts(list_make1(matviewRel), list_make1_oid(matviewOid),
+								NIL, DROP_RESTRICT, false);
+			CloseImmvIncrementalMaintenance();
+		}
+		else
+		{
+			Oid			OIDNewHeap;
+			DestReceiver *dest;
+			uint64		processed = 0;
+			Query	   *dataQuery = rewriteQueryForIMMV(query, NIL);
+			char		relpersistence = matviewRel->rd_rel->relpersistence;
+
+			/*
+			 * Create the transient table that will receive the regenerated data. Lock
+			 * it against access by any other process until commit (by which time it
+			 * will be gone).
+			 */
+			OIDNewHeap = make_new_heap(matviewOid, matviewRel->rd_rel->reltablespace,
+									   relpersistence,  ExclusiveLock);
+			LockRelationOid(OIDNewHeap, AccessExclusiveLock);
+			dest = CreateTransientRelDestReceiver(OIDNewHeap);
+
+			/* Generate the data */
+			processed = refresh_immv_datafill(dest, dataQuery, NULL, NULL, "");
+			refresh_by_heap_swap(matviewOid, OIDNewHeap, relpersistence);
+
+			/* Inform cumulative stats system about our activity */
+			pgstat_count_truncate(matviewRel);
+			pgstat_count_heap_insert(matviewRel, processed);
+		}
+
+		/* Clean up hash entry and delete tuplestores */
+		clean_up_IVM_hash_entry(entry);
+
+		/* Pop the original snapshot. */
+		PopActiveSnapshot();
+
+		table_close(matviewRel, NoLock);
+
+		/* Roll back any GUC changes */
+		AtEOXact_GUC(false, save_nestlevel);
+
+		/* Restore userid and security context */
+		SetUserIdAndSecContext(save_userid, save_sec_context);
+
+		return PointerGetDatum(NULL);
+	}
+
 	/*
 	 * rewrite query for calculating deltas
 	 */

sql/pg_ivm.sql

@@ -31,6 +31,17 @@ SELECT * FROM mv_ivm_1 ORDER BY 1,2,3;
 ROLLBACK;
 SELECT * FROM mv_ivm_1 ORDER BY 1,2,3;
 
+-- TRUNCATE a base table in join views
+BEGIN;
+TRUNCATE mv_base_a;
+SELECT * FROM mv_ivm_1;
+ROLLBACK;
+
+BEGIN;
+TRUNCATE mv_base_b;
+SELECT * FROM mv_ivm_1;
+ROLLBACK;
+
 -- some query syntax
 BEGIN;
 CREATE FUNCTION ivm_func() RETURNS int LANGUAGE 'sql'
@@ -71,6 +82,14 @@ INSERT INTO mv_base_a VALUES(2,100);
 SELECT * FROM mv_ivm_agg ORDER BY 1,2,3;
 ROLLBACK;
 
+-- TRUNCATE a base table in aggregate views
+BEGIN;
+SELECT create_immv('mv_ivm_agg', 'SELECT i, SUM(j), COUNT(*) FROM mv_base_a GROUP BY i');
+TRUNCATE mv_base_a;
+SELECT sum, count FROM mv_ivm_agg;
+SELECT i, SUM(j), COUNT(*) FROM mv_base_a GROUP BY i;
+ROLLBACK;
+
 -- support aggregate functions without GROUP clause
 BEGIN;
 SELECT create_immv('mv_ivm_group',  'SELECT SUM(j), COUNT(j), AVG(j) FROM mv_base_a');
@@ -81,6 +100,14 @@ DELETE FROM mv_base_a;
 SELECT * FROM mv_ivm_group ORDER BY 1;
 ROLLBACK;
 
+-- TRUNCATE a base table in aggregate views without GROUP clause
+BEGIN;
+SELECT create_immv('mv_ivm_group', 'SELECT SUM(j), COUNT(j), AVG(j) FROM mv_base_a');
+TRUNCATE mv_base_a;
+SELECT sum, count, avg FROM mv_ivm_group;
+SELECT SUM(j), COUNT(j), AVG(j) FROM mv_base_a;
+ROLLBACK;
+
 -- resolved issue: When use AVG() function and values is indivisible, result of AVG() is incorrect.
 BEGIN;
 SELECT create_immv('mv_ivm_avg_bug', 'SELECT i, SUM(j), COUNT(j), AVG(j) FROM mv_base_A GROUP BY i');