| From: | dan(at)sidhe(dot)org |
|---|---|
| To: | "Scott Marlowe" <scott(dot)marlowe(at)gmail(dot)com> |
| Cc: | dan(at)sidhe(dot)org,"Robert Haas" <robertmhaas(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Trying to track down weird query stalls |
| Date: | 2009-03-30 20:02:28 |
| Message-ID: | 56164.199.172.169.17.1238443348.squirrel@localhost |
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| Lists: | pgsql-performance |
> On Mon, Mar 30, 2009 at 1:42 PM, <dan(at)sidhe(dot)org> wrote:
>>> On Mon, Mar 30, 2009 at 12:42 PM, <dan(at)sidhe(dot)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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