Re: deadlock in single-row select-for-update + update scenario? How could it happen?

hubert depesz lubaczewski wrote:
> I have developer with pg 9.3.5, which is reporing something really strange.
>
> He runs importer, which does, in single transaction:
>
> begin;
> select * from table where pkey = <value> limit 1 for update;
> update table set ... where pkey = <the same_value>;
> commit;
>
> and two backends running the same transaction deadlock.

FWIW this problem was reported also by Andrew Sackville-West at
http://www.postgresql.org/message-id/20140731233051.GN17765@andrew-ThinkPad-X230

I strongly suspect now that the problem is related to the locking of
updated versions as heap_lock_tuple_updated, and perhaps the internal
locking done by EvalPlanQual. Haven't traced through it.

--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services