Re: [PATCH] lock_timeout and common SIGALRM framework

On 05/04/12 08:02, Boszormenyi Zoltan wrote:
> 2012-04-04 21:30 keltezéssel, Alvaro Herrera írta:
>> I think this patch is doing two things: first touching infrastructure
>> stuff and then adding lock_timeout on top of that. Would it work to
>> split the patch in two pieces?
>>
>
> Sure. Attached is the split version.
>
> Best regards,
> Zoltán Böszörményi
>
Hi,

I've started looking at and testing both patches.

Technically speaking, I think the source looks much better than the
first version of lock timeout, and may help adding other timeouts in the
future. I haven't tested it in depth though, because I encountered the
following problem:

While testing the patch, I found a way to crash PG. But what's weird is
that it crashes also with an unpatched git version.

Here is the way to reproduce it (I have done it with a pgbench schema):

- Set a small statement_timeout (just to save time during the tests)

Session1:
=#BEGIN;
=#lock TABLE pgbench_accounts ;

Session 2:
=#BEGIN;
=#lock TABLE pgbench_accounts ;
ERROR: canceling statement due to statement timeout
=# lock TABLE pgbench_accounts ;

I'm using \set ON_ERROR_ROLLBACK INTERACTIVE by the way. It can also be
done with a rollback to savepoint of course.

Session 2 crashes with this : TRAP : FailedAssertion(«
!(locallock->holdsStrongLockCount == 0) », fichier : « lock.c », ligne :
749).

It can also be done without a statement_timeout, and a control-C on the
second lock table.

I didn't touch anything but this. It occurs everytime, when asserts are
activated.

I tried it on 9.1.3, and I couldn't make it crash with the same sequence
of events. So maybe it's something introduced since ? Or is the assert
still valid ?

Cheers