Marti Raudsepp <marti@xxxxxxxxx> Wrote in message: > Hi > > On Tue, Oct 21, 2014 at 12:53 PM, Ilya I. Ashchepkov <koctep@xxxxxxxxx> 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 > > > -- > Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-general > > Thank you. I tried execute and it helps. -- -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
