From: dan@sidhe.org
To: Scott Marlowe <scott.marlowe@gmail.com>
Cc: dan@sidhe.org,"Robert Haas" <robertmhaas@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Trying to track down weird query stalls
Date: Mon, 30 Mar 2009 16:02:28 -0400 (EDT)
Message-ID: <56164.199.172.169.17.1238443348.squirrel@localhost> (raw)
In-Reply-To: <dcc563d10903301247t58bef7cbsd0b6d3bbd1a5e046@mail.gmail.com>
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<56921.199.172.169.36.1238438533.squirrel@localhost>
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<dcc563d10903301247t58bef7cbsd0b6d3bbd1a5e046@mail.gmail.com>
> On Mon, Mar 30, 2009 at 1:42 PM, <dan@sidhe.org> wrote:
>>> On Mon, Mar 30, 2009 at 12:42 PM, <dan@sidhe.org> wrote:
>>>> Arguably in this case the actual query should run faster than the
>>>> EXPLAIN
>>>> ANALYZE version, since the cache is hot. (Though that'd only likely
>>>> shave
>>>> a few dozen ms off the runtime)
>>>
>>> Joining a lot of tables together? Could be GEQO kicking in.
>>
>> Only if I get different query plans for the query depending on whether
>> it's being EXPLAIN ANALYZEd or not. That seems unlikely...
>
> Yes, you can. In fact you often will. Not because it's being
> explained or not, just because that's how GEQO works.
Ouch. I did *not* know that was possible -- I assumed that the plan was
deterministic and independent of explain analyze. The query has seven
tables (one of them a temp table) and my geqo_threshold is set to 12. If
I'm reading the docs right GEQO shouldn't kick in.
-Dan
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To: pgsql-performance@postgresql.org
Cc: dan@sidhe.org, scott.marlowe@gmail.com, robertmhaas@gmail.com
Subject: Re: Trying to track down weird query stalls
In-Reply-To: <56164.199.172.169.17.1238443348.squirrel@localhost>
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