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Re: Querying distinct values from a large table
- From: Richard Huxton <dev(at)archonet(dot)com>
- To: Simon Riggs <simon(at)2ndquadrant(dot)com>
- Cc: Igor Lobanov <ilobanov(at)swsoft(dot)com>, pgsql-performance(at)postgresql(dot)org
- Subject: Re: Querying distinct values from a large table
- Date: Tue, 30 Jan 2007 14:11:48 +0000
Simon Riggs wrote:
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 msAll your time is in the sort, not in the SeqScan. Increase your work_mem.
Well, even if the sort was instant it's only going to get him down to 20secs.
-- Richard Huxton Archonet Ltd
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- Querying distinct values from a large table
- From: Igor Lobanov
- Re: Querying distinct values from a large table
- From: Richard Huxton
- Re: Querying distinct values from a large table
- From: Igor Lobanov
- Re: Querying distinct values from a large table
- From: Simon Riggs
- Querying distinct values from a large table
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