From: Vik Fearing <vik.fearing@dalibo.com>
To: Scott Marlowe <scott.marlowe@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: subselect requires offset 0 for good performance.
Date: Fri, 09 Aug 2013 00:09:17 +0200
Message-ID: <5204170D.4020608@dalibo.com> (raw)
In-Reply-To: <51FB61C8.4090206@dalibo.com>
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On 08/02/2013 09:37 AM, Vik Fearing wrote:
> EXPLAIN ANALYZE
> WITH RECURSIVE
> x (start_time) AS
> (
> SELECT generate_series(1, 1000000)
> ),
> t (time, timeround) AS
> (
> SELECT time, time - time % 900000 AS timeround
> FROM (SELECT min(start_time) AS time FROM x) AS tmp
> UNION ALL
> SELECT time, time - time % 900000
> FROM (SELECT (SELECT min(start_time) AS time
> FROM x
> WHERE start_time >= t.timeround + 900000)
> FROM t
> WHERE t.time IS NOT NULL OFFSET 0
> ) tmp
> )
> SELECT count(*) FROM t WHERE time IS NOT NULL;
>
> If you remove the OFFSET 0, you'll see two more subplans (because "time"
> is referenced three times).
Is this not interesting to anyone?
Vik
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To: pgsql-performance@postgresql.org
Cc: vik.fearing@dalibo.com, scott.marlowe@gmail.com, tgl@sss.pgh.pa.us
Subject: Re: subselect requires offset 0 for good performance.
In-Reply-To: <5204170D.4020608@dalibo.com>
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