Thomas Munro wrote:
> On 25 August 2014 02:57, Alvaro Herrera <> wrote:
> > Thomas Munro wrote:
> >> The difficulty of course will be testing all these racy cases 
> >> reproducibly...
> >
> > Does this help?
> >
> > 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.


Álvaro Herrera      
PostgreSQL Development, 24x7 Support, Training & Services

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