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Message-ID: <48680AA4.2070800@gmail.com>
Date: Sun, 29 Jun 2008 18:20:20 -0400
From: John Beaver <john.e.beaver@gmail.com>
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To: Jeremy Harris <jgh@wizmail.org>
CC: Pgsql-Performance <pgsql-performance@postgresql.org>
Subject: Re: sequence scan problem
References: <48680418.7030708@gmail.com> <48680860.2000300@wizmail.org>
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Jeremy Harris wrote:
> John Beaver wrote:
>> I'm having a strange problem with a query. The query is fairly 
>> simple, with a few constants and two joins. All relevant columns 
>> should be indexed, and I'm pretty sure there aren't any type 
>> conversion issues. But the query plan includes a fairly heavy seq 
>> scan. The only possible complication is that the tables involved are 
>> fairly large - hundreds of millions of rows each.
>>
>> Can anyone explain this? There should only ever be a maximum of about 
>> 50 rows returned when the query is executed.
>
> You didn't say when you last vacuumed?
I ran 'vacuum analyze' on both tables directly after I finished building 
them, and I haven't updated their contents since.
> If there should only be 50 rows returned then the estimates from the
> planner are way out.
>
> If that doesn't help, we'll need version info, and (if you can afford
> the time) an "explain analyze"
Sure, I'm running it now. I'll send the results when it's done, but yes, 
it could take a while.
>
> Cheers,
>  Jeremy
>