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Re: Query slow as Function

From: Andreas Kretschmer <akretschmer(at)spamfence(dot)net>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Query slow as Function
Date: 2012-02-18 16:02:44
Message-ID: 20120218160244.GA23315@tux (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Steve Horn <steve(at)stevehorn(dot)cc> wrote:

> Execute the function: select * from geocode_carrier_route_by_geocode('xyz');
> This query takes 500 milliseconds to run. My question of course is why?

Wild guess:

The planner doesn't know the actual value of the input-parameter, so the
planner doesn't use the Index.

> Related: If I create a function and assign LANGUAGE 'sql', my function runs in
> the expected 10 milliseconds. Is there some overhead to using the plpgsql
> language?

The planner, in this case, knows the actual value.

> Thanks for any help in clarifying my understanding!

You can check the plan with the auto_explain - Extension, and you can
force the planner to create a plan based on the actual input-value by
using dynamic SQL (EXECUTE 'your query string' inside the function)

As i said, wild guess ...

Really, I'm not out to destroy Microsoft. That will just be a completely
unintentional side effect.                              (Linus Torvalds)
"If I was god, I would recompile penguin with --enable-fly."   (unknown)
Kaufbach, Saxony, Germany, Europe.              N 51.05082°, E 13.56889°

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