From: Alban Hertroys <haramrae@gmail.com>
To: Jose Martinez <jmartinez@opencrowd.com>
Cc: pgsql-general@postgresql.org
Cc: pgsql-admin@postgresql.org
Subject: Re: Simple Query Very Slow
Date: Sat, 22 Dec 2012 13:06:21 +0100
Message-ID: <79F38E90-60F7-45AC-A3A0-E1EAC42515D6@gmail.com> (raw)
In-Reply-To: <CA+ixmX37YK+RZcLab_xXKywojFG8sXJFpHD3GWGZqNoo8yRrVA@mail.gmail.com>
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> and here's my query
>
> select * from ticket
> where created between '2012-12-19 00:00:00' and '2012-12-20 00:00:00'
>
> This was working fine until the number of records started to grow (about 5 million) and now it's taking forever to return.
>
> Explain analyze reveals this:
>
> "Index Scan using ticket_1_idx on ticket (cost=0.00..10202.64 rows=52543 width=1297) (actual time=0.109..125.704 rows=53340 loops=1)"
> " Index Cond: ((created >= '2012-12-19 00:00:00+00'::timestamp with time zone) AND (created <= '2012-12-20 00:00:00+00'::timestamp with time zone))"
> "Total runtime: 175.853 ms"
> Nothing works. What am I doing wrong? why is it selecting sequential scan? the indexes are supposed to make the query fast. Anything that can be done to optimize it?
It is not selecting sequential scan, you're looking at an index scan. That should be pretty fast, and it isn't that slow - that's still sub-second performance (0.176s).
Is that explain from the correct table? According to the results there are but 53 thousand rows in it, not anywhere near 5 million.
Perhaps your index got bloated? Do you have any long-running transactions still active that prevent cleaning up deprecated index entries? If that's the case, close the application that keeps that connection open and run a vacuum.
Are you vacuuming that table often enough?
If none of that helps, perhaps a REINDEX does.
Is that a dedicated database machine or is it also doing other stuff that's eating up resources?
You didn't mention what version of Postgres you're on or what OS you're using.
Alban Hertroys
--
Screwing up is an excellent way to attach something to the ceiling.
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To: pgsql-admin@postgresql.org
Cc: haramrae@gmail.com, jmartinez@opencrowd.com, pgsql-general@postgresql.org
Subject: Re: Simple Query Very Slow
In-Reply-To: <79F38E90-60F7-45AC-A3A0-E1EAC42515D6@gmail.com>
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