I've found an issue with updatable security barrier views. Locking is
being pushed down into the subquery. Locking is thus applied before
user-supplied quals are, so we potentially lock too many rows.
I'm looking into the code now, but in the mean time, here's a demo of
the problem:
regress=> CREATE TABLE t1(x integer, y integer);
CREATE TABLE
regress=> INSERT INTO t1(x,y) VALUES (1,1), (2,2), (3,3), (4,4);
INSERT 0 4
regress=> CREATE VIEW v1 WITH (security_barrier) AS SELECT x, y FROM t1
WHERE x % 2 = 0;
CREATE VIEW
regress=> EXPLAIN SELECT * FROM v1 FOR UPDATE;
QUERY PLAN
-----------------------------------------------------------------------
LockRows (cost=0.00..42.43 rows=11 width=40)
-> Subquery Scan on v1 (cost=0.00..42.32 rows=11 width=40)
-> LockRows (cost=0.00..42.21 rows=11 width=14)
-> Seq Scan on t1 (cost=0.00..42.10 rows=11 width=14)
Filter: ((x % 2) = 0)
Planning time: 0.140 ms
(6 rows)
or, preventing pushdown with a wrapper function to demonstrate the problem:
regress=> CREATE FUNCTION is_one(integer) RETURNS boolean AS $$ DECLARE
result integer; BEGIN SELECT $1 = 1
regress=> EXPLAIN SELECT * FROM v1 WHERE is_one(x) FOR UPDATE;
QUERY PLAN
-----------------------------------------------------------------------
LockRows (cost=0.00..45.11 rows=4 width=40)
-> Subquery Scan on v1 (cost=0.00..45.07 rows=4 width=40)
Filter: is_one(v1.x)
-> LockRows (cost=0.00..42.21 rows=11 width=14)
-> Seq Scan on t1 (cost=0.00..42.10 rows=11 width=14)
Filter: ((x % 2) = 0)
Planning time: 0.147 ms
(7 rows)
OK, so it looks like the code:
/*
* Now deal with any PlanRowMark on this RTE by requesting a
lock
* of the same strength on the RTE copied down to the subquery.
*/
rc = get_plan_rowmark(root->rowMarks, rt_index);
if (rc != NULL)
{
switch (rc->markType)
{
/* .... */
}
root->rowMarks = list_delete(root->rowMarks, rc);
}
isn't actually appropriate. We should _not_ be pushing locking down into
the subquery.
Instead, we should be retargeting the rowmark so it points to the new
subquery RTE, marking rows _after_filtering. We want a plan like:
regress=> EXPLAIN SELECT * FROM v1 WHERE is_one(x) FOR UPDATE;
QUERY PLAN
-----------------------------------------------------------------------
LockRows (cost=0.00..45.11 rows=4 width=40)
-> Subquery Scan on v1 (cost=0.00..45.07 rows=4 width=40)
Filter: is_one(v1.x)
-> Seq Scan on t1 (cost=0.00..42.10 rows=11 width=14)
Filter: ((x % 2) = 0)
Planning time: 0.147 ms
(7 rows)
I'm not too sure what the best way to do that is. Time permitting I'll
see if I can work out the RowMark code and set something up.
--
Craig Ringer http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
--
Sent via pgsql-hackers mailing list ([email protected])
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
