Fix FK checks of TRUNCATE involving partitioned tables

When truncating a table that is referenced by foreign keys in
partitioned tables, the check to ensure the referencing table are also
truncated spuriously failed.  This is because it was relying on
relhastriggers as a proxy for the table having FKs, and that's wrong for
partitioned tables.  Fix it to consider such tables separately.  There
may be a better way ... but this code is pretty inefficient already.

Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Michael Paquiër <michael@paquier.xyz>
Discussion: https://postgr.es/m/20180711000624.zmeizicibxeehhsg@alvherre.pgsql

src/backend/catalog/heap.c

@@ -3181,13 +3181,16 @@ heap_truncate_check_FKs(List *relations, bool tempTables)
 	 * Build a list of OIDs of the interesting relations.
 	 *
 	 * If a relation has no triggers, then it can neither have FKs nor be
-	 * referenced by a FK from another table, so we can ignore it.
+	 * referenced by a FK from another table, so we can ignore it.  For
+	 * partitioned tables, FKs have no triggers, so we must include them
+	 * anyway.
 	 */
 	foreach(cell, relations)
 	{
 		Relation	rel = lfirst(cell);
 
-		if (rel->rd_rel->relhastriggers)
+		if (rel->rd_rel->relhastriggers ||
+			rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
 			oids = lappend_oid(oids, RelationGetRelid(rel));
 	}
 

src/backend/commands/tablecmds.c

@@ -1421,7 +1421,7 @@ ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
 	Oid		   *logrelids;
 
 	/*
-	 * Open, exclusive-lock, and check all the explicitly-specified relations
+	 * Check the explicitly-specified relations.
 	 *
 	 * In CASCADE mode, suck in all referencing relations as well.  This
 	 * requires multiple iterations to find indirectly-dependent relations. At

src/test/regress/expected/truncate.out

@@ -464,3 +464,78 @@ ERROR:  cannot truncate only a partitioned table
 HINT:  Do not specify the ONLY keyword, or use TRUNCATE ONLY on the partitions directly.
 TRUNCATE truncparted;
 DROP TABLE truncparted;
+-- foreign key on partitioned table: partition key is referencing column.
+-- Make sure truncate did execute on all tables
+CREATE FUNCTION tp_ins_data() RETURNS void LANGUAGE plpgsql AS $$
+  BEGIN
+	INSERT INTO truncprim VALUES (1), (100), (150);
+	INSERT INTO truncpart VALUES (1), (100), (150);
+  END
+$$;
+CREATE FUNCTION tp_chk_data(OUT pktb regclass, OUT pkval int, OUT fktb regclass, OUT fkval int)
+  RETURNS SETOF record LANGUAGE plpgsql AS $$
+  BEGIN
+    RETURN QUERY SELECT
+      pk.tableoid::regclass, pk.a, fk.tableoid::regclass, fk.a
+    FROM truncprim pk FULL JOIN truncpart fk USING (a)
+    ORDER BY 2, 4;
+  END
+$$;
+CREATE TABLE truncprim (a int PRIMARY KEY);
+CREATE TABLE truncpart (a int REFERENCES truncprim)
+  PARTITION BY RANGE (a);
+CREATE TABLE truncpart_1 PARTITION OF truncpart FOR VALUES FROM (0) TO (100);
+CREATE TABLE truncpart_2 PARTITION OF truncpart FOR VALUES FROM (100) TO (200)
+  PARTITION BY RANGE (a);
+CREATE TABLE truncpart_2_1 PARTITION OF truncpart_2 FOR VALUES FROM (100) TO (150);
+CREATE TABLE truncpart_2_d PARTITION OF truncpart_2 DEFAULT;
+TRUNCATE TABLE truncprim;	-- should fail
+ERROR:  cannot truncate a table referenced in a foreign key constraint
+DETAIL:  Table "truncpart" references "truncprim".
+HINT:  Truncate table "truncpart" at the same time, or use TRUNCATE ... CASCADE.
+select tp_ins_data();
+ tp_ins_data 
+-------------
+ 
+(1 row)
+
+-- should truncate everything
+TRUNCATE TABLE truncprim, truncpart;
+select * from tp_chk_data();
+ pktb | pkval | fktb | fkval 
+------+-------+------+-------
+(0 rows)
+
+select tp_ins_data();
+ tp_ins_data 
+-------------
+ 
+(1 row)
+
+-- should truncate everything
+SET client_min_messages TO WARNING;	-- suppress cascading notices
+TRUNCATE TABLE truncprim CASCADE;
+RESET client_min_messages;
+SELECT * FROM tp_chk_data();
+ pktb | pkval | fktb | fkval 
+------+-------+------+-------
+(0 rows)
+
+SELECT tp_ins_data();
+ tp_ins_data 
+-------------
+ 
+(1 row)
+
+-- should truncate all partitions
+TRUNCATE TABLE truncpart;
+SELECT * FROM tp_chk_data();
+   pktb    | pkval | fktb | fkval 
+-----------+-------+------+-------
+ truncprim |     1 |      |      
+ truncprim |   100 |      |      
+ truncprim |   150 |      |      
+(3 rows)
+
+DROP TABLE truncprim, truncpart;
+DROP FUNCTION tp_ins_data(), tp_chk_data();

src/test/regress/sql/truncate.sql

@@ -244,3 +244,50 @@ INSERT INTO truncparted VALUES (1, 'a');
 TRUNCATE ONLY truncparted;
 TRUNCATE truncparted;
 DROP TABLE truncparted;
+
+-- foreign key on partitioned table: partition key is referencing column.
+-- Make sure truncate did execute on all tables
+CREATE FUNCTION tp_ins_data() RETURNS void LANGUAGE plpgsql AS $$
+  BEGIN
+	INSERT INTO truncprim VALUES (1), (100), (150);
+	INSERT INTO truncpart VALUES (1), (100), (150);
+  END
+$$;
+CREATE FUNCTION tp_chk_data(OUT pktb regclass, OUT pkval int, OUT fktb regclass, OUT fkval int)
+  RETURNS SETOF record LANGUAGE plpgsql AS $$
+  BEGIN
+    RETURN QUERY SELECT
+      pk.tableoid::regclass, pk.a, fk.tableoid::regclass, fk.a
+    FROM truncprim pk FULL JOIN truncpart fk USING (a)
+    ORDER BY 2, 4;
+  END
+$$;
+CREATE TABLE truncprim (a int PRIMARY KEY);
+CREATE TABLE truncpart (a int REFERENCES truncprim)
+  PARTITION BY RANGE (a);
+CREATE TABLE truncpart_1 PARTITION OF truncpart FOR VALUES FROM (0) TO (100);
+CREATE TABLE truncpart_2 PARTITION OF truncpart FOR VALUES FROM (100) TO (200)
+  PARTITION BY RANGE (a);
+CREATE TABLE truncpart_2_1 PARTITION OF truncpart_2 FOR VALUES FROM (100) TO (150);
+CREATE TABLE truncpart_2_d PARTITION OF truncpart_2 DEFAULT;
+
+TRUNCATE TABLE truncprim;	-- should fail
+
+select tp_ins_data();
+-- should truncate everything
+TRUNCATE TABLE truncprim, truncpart;
+select * from tp_chk_data();
+
+select tp_ins_data();
+-- should truncate everything
+SET client_min_messages TO WARNING;	-- suppress cascading notices
+TRUNCATE TABLE truncprim CASCADE;
+RESET client_min_messages;
+SELECT * FROM tp_chk_data();
+
+SELECT tp_ins_data();
+-- should truncate all partitions
+TRUNCATE TABLE truncpart;
+SELECT * FROM tp_chk_data();
+DROP TABLE truncprim, truncpart;
+DROP FUNCTION tp_ins_data(), tp_chk_data();