From: Shaun Thomas <sthomas@optionshouse.com>
To: Andrew Jaimes <andrewjaimes@hotmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Sequencial scan in a JOIN
Date: Tue, 5 Jun 2012 08:15:45 -0500
Message-ID: <4FCE0681.5040306@optionshouse.com> (raw)
In-Reply-To: <BLU161-W1125BE7D5AED110518DEFFDD0C0@phx.gbl>
References: <BLU161-W1125BE7D5AED110518DEFFDD0C0@phx.gbl>
On 06/05/2012 07:48 AM, Andrew Jaimes wrote:
> ' -> Hash Join (cost=10.93..99795.09 rows=242803 width=0) (actual
> time=0.541..2249.027 rows=33 loops=1)'
> ' Hash Cond: ((a_activity.activequeueid = l_userqueue.queueid)
> AND (a_activity.sbuid = e_usersessions.sbuid))'
> ' -> Seq Scan on a_activity (cost=0.00..88462.52 rows=1208167
> width=22) (actual time=0.010..1662.142
I'd be willing to bet your stats are way, way off. It expected 242,803
rows in the hash, but only got 33. In that kind of scenario, I could
easily see the planner choosing a sequence scan over an index scan, as
doing that many index seeks would be much more expensive than scanning
the table.
What's your default_statistics_target, and when is the last time you
analyzed the tables in this query?
--
Shaun Thomas
OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604
312-444-8534
sthomas@optionshouse.com
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To: pgsql-performance@postgresql.org
Cc: sthomas@optionshouse.com, andrewjaimes@hotmail.com
Subject: Re: Sequencial scan in a JOIN
In-Reply-To: <4FCE0681.5040306@optionshouse.com>
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