Re: SKIP LOCKED DATA (work in progress)

On 27 August 2014 17:18, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
> Thomas Munro wrote:
>> On 25 August 2014 02:57, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
>> > Thomas Munro wrote:
>> >> The difficulty of course will be testing all these racy cases reproducibly...
>> >
>> > Does this help?
>> > http://www.postgresql.org/message-id/51FB4305.3070600@2ndquadrant.com
>> > The useful trick there is forcing a query to get its snapshot and then
>> > go to sleep before actually doing anything, by way of an advisory lock.
>>
>> Yes it does, thanks Alvaro and Craig.  I think the attached spec
>> reproduces the problem using that trick, ie shows NOWAIT blocking,
>> presumably in EvalPlanQualFetch (though I haven't stepped through it
>> with a debugger yet).  I'm afraid I'm out of Postgres hacking cycles
>> for a few days, but next weekend I should have a new patch that fixes
>> this by teaching EvalPlanQualFetch about wait policies, with isolation
>> tests for NOWAIT and SKIP LOCKED.
>
> Hmm, http://www.postgresql.org/message-id/51FB6703.9090801@2ndquadrant.com

Thanks, I hadn't seen this, I should have checked the archives better.
I have actually already updated my patch to handle EvalPlanQualFetch
with NOWAIT and SKIP LOCKED with isolation specs, see attached.  I
will compare with Craig's and see if I screwed anything up... of
course I am happy to merge and submit a new patch on top of Craig's if
it's going to be committed.

I haven't yet figured out how to get get into a situation where
heap_lock_updated_tuple_rec waits.

Best regards,
Thomas Munro