Re: Deadlock on the same select for update

In response to Roman <roman(dot)janowczyk(at)gmail(dot)com>:

> Hi,
> I have problem with deadlocks and don't know why it happens. Below is
> the log (postgres 9.0, debian):
>
> [11882]DETAIL: Process 11882 waits for ShareLock on transaction
> 44324308; blocked by process 11884.
> Process 11884 waits for ShareLock on transaction 44324307;
> blocked by process 11882.
>
> Process 11882: SELECT * FROM teddy WHERE id IN
> (112747007,112747008,112747011,112747013,112747015,112747016,112747020,112747021,112747022,112747024,112747025,112747028,112747030,112747032,112747034,112747035,112747038,112747043,112747044,112747045,112747050,112747052,112747053)
> FOR UPDATE
>
> Process 11884: SELECT * FROM teddy WHERE id IN
> (112747007,112747008,112747011,112747013,112747015,112747016,112747020,112747021,112747022,112747024,112747025,112747028,112747030,112747032,112747034,112747035,112747038,112747043,112747044,112747045,112747050,112747052,112747053)
> FOR UPDATE

My experience is that you have no guarantee what order SELECT FOR UPDATE
will lock those rows in, thus the chance for deadlock is there.

--
Bill Moran
http://www.potentialtech.com
http://people.collaborativefusion.com/~wmoran/