Re: [PATCH] lock_timeout and common SIGALRM framework

2012-04-06 14:47 keltezéssel, Cousin Marc írta:
> 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
>

Attached are the new patches. I rebased them to current GIT and
they are expected to be applied after Robert Haas' patch in the
"bug in fast-path locking" thread.

Now it survives the above scenario.

Best regards,
Zoltán Böszörményi

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Zoltán Böszörményi
Cybertec Schönig&  Schönig GmbH
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