From: Shaun Thomas <sthomas@optionshouse.com>
To: Kai Sellgren <kaisellgren@gmail.com>
To: pgsql-performance@postgresql.org
Subject: Re: Optimizing a query
Date: Thu, 19 Dec 2013 11:53:55 -0600
Message-ID: <52B332B3.9050402@optionshouse.com> (raw)
In-Reply-To: <CANyR-3cRezeFXaE6udHh=SEkO0BfAP2Aq5B=eo90n=WrqXnj_A@mail.gmail.com>
References: <CANyR-3cRezeFXaE6udHh=SEkO0BfAP2Aq5B=eo90n=WrqXnj_A@mail.gmail.com>
List-Unsubscribe: <mailto:majordomo@postgresql.org?body=unsub%20pgsql-performance>
On 12/17/2013 08:48 PM, Kai Sellgren wrote:
This is your select:
> SELECT *
> FROM "Log"
> LEFT JOIN "NewsArticle" ON "NewsArticle".id = "Log"."targetId" AND
> "Log"."targetType" = 'NewsArticle'
> ORDER BY "Log"."createdAt" DESC
> LIMIT 10
This is your index:
> CREATE INDEX "Log_targetId_targetType_idx"
> ON "Log"
> USING btree
> ("targetId", "targetType" COLLATE pg_catalog."default");
Unfortunately, this won't help you. You are not matching on any IDs you
indexed, aside from joining against the article table. You have no WHERE
clause to restrict the data set, so it absolutely must read the entire
table to find the most recent records. Without an index on "createdAt",
how is it supposed to know what the ten most recent records are?
Add an index to the createdAt column:
CREATE INDEX idx_log_createdat ON "Log" (createdAt DESC);
Using that, it should get the ten most recent Log records almost
immediately, including associated article content.
--
Shaun Thomas
OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604
312-676-8870
sthomas@optionshouse.com
______________________________________________
See http://www.peak6.com/email_disclaimer/ for terms and conditions related to this email
--
Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-performance
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: sthomas@optionshouse.com, kaisellgren@gmail.com
Subject: Re: Optimizing a query
In-Reply-To: <52B332B3.9050402@optionshouse.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox