From: Andy Colson <andy@squeakycode.net>
To: Matt White <mattw922@gmail.com>
To: pgsql-performance@postgresql.org
Subject: Re: Slow-ish Query Needs Some Love
Date: Tue, 02 Feb 2010 14:11:34 -0600
Message-ID: <4B6886F6.4080402@squeakycode.net> (raw)
In-Reply-To: <250b74b4-f38f-4dab-a8bc-91d6d152d46c@h9g2000prn.googlegroups.com>
References: <1d4feebf-ff4d-4463-b1c8-d1a12d27400c@z10g2000prh.googlegroups.com>
<hk9816$qh5$1@news.eternal-september.org>
<250b74b4-f38f-4dab-a8bc-91d6d152d46c@h9g2000prn.googlegroups.com>
On 2/2/2010 1:03 PM, Matt White wrote:
> On Feb 2, 6:06 am, Edgardo Portal<egportal2...@yahoo.com> wrote:
>> On 2010-02-02, Matt White<mattw...@gmail.com> wrote:
>>
>>> I have a relatively straightforward query that by itself isn't that
>>> slow, but we have to run it up to 40 times on one webpage load, so it
>>> needs to run much faster than it does. Here it is:
>>
>>> SELECT COUNT(*) FROM users, user_groups
>>> WHERE users.user_group_id = user_groups.id AND NOT users.deleted AND
>>> user_groups.partner_id IN
>>> (partner_id_1, partner_id_2);
>>
>>> The structure is partners have user groups which have users. In the
>>> test data there are over 200,000 user groups and users but only ~3000
>>> partners. Anyone have any bright ideas on how to speed this query up?
>>
>> Can you avoid running it 40 times, maybe by restructuring the
>> query (or making a view) along the lines of the following and
>> adding some logic to your page?
>>
>> SELECT p.partner_id, ug.user_group_id, u.id, count(*)
>> FROM partners p
>> LEFT JOIN user_groups ug
>> ON ug.partner_id=p.partner_id
>> LEFT JOIN users u
>> ON u.user_group_id=ug.id
>> WHERE NOT u.deleted
>> GROUP BY 1,2,3
>> ;
>
> Thanks for the suggestion. The view didn't seem to speed things up.
> Perhaps we can reduce the number of times it's called, we'll see. Any
> additional ideas would be helpful. Thanks.
I agree with Edgardo, I think the biggest time saver will be reducing
trips to the database.
But... do you have an index on users.user_group_id?
Does rewriting it change the plan any?
SELECT COUNT(*) FROM users
inner join user_groups on (users.user_group_id = user_groups.id)
where NOT users.deleted
AND user_groups.partner_id IN (partner_id_1, partner_id_2);
And... it looks like the row guestimate is off a litte:
Index Scan using user_groups_partner_id_idx
on user_groups
(cost=0.00..133.86 rows=3346 width=8)
(actual time=0.049..96.992 rows=100001 loops=2)
It guessed 3,346 rows, but actually got 100,001. Have you run an
analyze on it? If so, maybe bumping up the stats might help?
-Andy
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To: pgsql-performance@postgresql.org
Cc: andy@squeakycode.net, mattw922@gmail.com
Subject: Re: Slow-ish Query Needs Some Love
In-Reply-To: <4B6886F6.4080402@squeakycode.net>
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