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Re: Query tuning: partitioning, DISTINCT ON, and indexing - Mailing list pgsql-performance

From bricklen
Subject Re: Query tuning: partitioning, DISTINCT ON, and indexing
Date
Msg-id CAGrpgQ-gOVq3v=TaskKKwY5f=A5eoNvKCCKgxJugnO=paKJJPg@mail.gmail.com
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In response to Query tuning: partitioning, DISTINCT ON, and indexing  (Maciek Sakrejda <m.sakrejda@gmail.com>)
Responses Re: Query tuning: partitioning, DISTINCT ON, and indexing  (Maciek Sakrejda <m.sakrejda@gmail.com>)
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On Thu, Jun 20, 2013 at 6:24 PM, Maciek Sakrejda <m.sakrejda@gmail.com> wrote:
SELECT
  DISTINCT ON (type) ts, type, details
FROM
  observations
WHERE
  subject = '...'
ORDER BY
  type, ts DESC;

First thing: What is your "work_mem" set to, and how much RAM is in the machine? If you look at the plan, you'll immediately notice the "external merge Disk" line where it spills to disk on the sort. Try setting your work_mem to 120MB or so (depending on how much RAM you have, # concurrent sessions, complexity of queries etc)

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