Re: Concurrency bug in UPDATE of partition-key

On Tue, Jun 5, 2018 at 8:03 PM, Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com>
wrote:

> Attached is a rebased patch version. Also included it in the upcoming
> commitfest :
> https://commitfest.postgresql.org/18/1660/
>
> In the rebased version, the new test cases are added in the existing
> isolation/specs/partition-key-update-1.spec test.

/*
+ * If this is part of an UPDATE of partition-key, the
+ * epq tuple will contain the changes from this
+ * transaction over and above the updates done by the
+ * other transaction. The caller should now use this
+ * tuple as its NEW tuple, rather than the earlier NEW
+ * tuple.
+ */
+ if (epqslot)
+ {
+ *epqslot = my_epqslot;
+ return NULL;
+ }

I think we need simmilar fix if there are BR Delete trigger and the
ExecDelete is blocked on heap_lock_tuple because the concurrent transaction
is updating the same row. Because in such case it would have already got
the final tuple so the hep_delete will return MayBeUpdated.

Below test can reproduce the issue.

CREATE TABLE pa_target (key integer, val text) PARTITION BY LIST (key);
CREATE TABLE part1 PARTITION OF pa_target FOR VALUES IN (1);
CREATE TABLE part2 PARTITION OF pa_target FOR VALUES IN (2);

CREATE TABLE deleted_row (count int);
CREATE OR REPLACE FUNCTION br_delete() RETURNS trigger AS
$$BEGIN
insert into deleted_row values(OLD.key);
RETURN OLD;
END;$$ LANGUAGE plpgsql;

CREATE TRIGGER test_br_trig BEFORE DELETE ON part1 FOR EACH ROW EXECUTE
PROCEDURE br_delete();

INSERT INTO pa_target VALUES (1, 'initial1');

session1:
postgres=# BEGIN;
BEGIN
postgres=# UPDATE pa_target SET val = val || ' updated by update1' WHERE
key = 1;
UPDATE 1

session2:
postgres=# UPDATE pa_target SET val = val || ' updated by update2', key =
key + 1 WHERE key =1;
<block>

session1:
postgres=# commit;
COMMIT

UPDATE 1
postgres=# select * from pa_target ;
key | val
-----+-----------------------------
2 | initial1 updated by update2 --> session1's update is overwritten.

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com