| From: | Vik Fearing <vik(dot)fearing(at)dalibo(dot)com> |
|---|---|
| To: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: subselect requires offset 0 for good performance. |
| Date: | 2013-08-08 22:09:17 |
| Message-ID: | 5204170D.4020608@dalibo.com |
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| Thread: | |
| Lists: | pgsql-performance |
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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