| From: | "Simon Riggs" <simon(at)2ndquadrant(dot)com> |
|---|---|
| To: | "Igor Lobanov" <ilobanov(at)swsoft(dot)com> |
| Cc: | "Richard Huxton" <dev(at)archonet(dot)com>, <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Querying distinct values from a large table |
| Date: | 2007-01-30 14:04:15 |
| Message-ID: | 1170165856.3681.54.camel@silverbirch.site |
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| Thread: | |
| Lists: | pgsql-performance |
On Tue, 2007-01-30 at 15:33 +0600, Igor Lobanov wrote:
> explain analyze select distinct a, b from tbl
>
> EXPLAIN ANALYZE output is:
>
> Unique (cost=500327.32..525646.88 rows=1848 width=6) (actual
> time=52719.868..56126.356 rows=5390 loops=1)
> -> Sort (cost=500327.32..508767.17 rows=3375941 width=6) (actual
> time=52719.865..54919.989 rows=3378864 loops=1)
> Sort Key: a, b
> -> Seq Scan on tbl (cost=0.00..101216.41 rows=3375941
> width=6) (actual time=16.643..20652.610 rows=3378864 loops=1)
> Total runtime: 57307.394 ms
All your time is in the sort, not in the SeqScan.
Increase your work_mem.
--
Simon Riggs
EnterpriseDB http://www.enterprisedb.com
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