Marti Raudsepp <marti@juffo.org> Wrote in message:
> Hi
>
> On Tue, Oct 21, 2014 at 12:53 PM, Ilya I. Ashchepkov <koctep@gmail.com> wrote:
>> I wrote a function and during testing it I came across the strange
>> behaviour.
>> Function runtime is about 200ms first 5 times, 6th and futher calls takes
>> ~22000 ms.
>> I simplified my schema, you can see it in attached file.
>> I've tested on 9.4beta3 and 9.3.5.
>
> I didn't look at the test case. But most likely the problem is that
> after 5 executions, plancache decides that a generic plan is no more
> expensive than a custom plan, and reverts to executing the generic
> one. But in reality there is a big difference in execution time.
>
> See this for how the logic works:
> https://github.com/postgres/postgres/blob/master/src/backend/utils/cache/plancache.c#L1036
>
> As a workaround you could use PL/pgSQL EXECUTE to run the query, which
> isn't subject to generic plans:
> http://www.postgresql.org/docs/current/static/plpgsql-statements.html#PLPGSQL-STATEMENTS-EXECUTING-DYN
>
> Regards,
> Marti
>
>
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>
Thank you. I tried execute and it helps.
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