Re: Index not being used - Mailing list pgsql-general
From | Ralph Smith |
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Subject | Re: Index not being used |
Date | |
Msg-id | 98B259D4-A190-4A8D-A7C7-5E3ABA1DBF5C@u.washington.edu Whole thread Raw |
In response to | Re: Index not being used ("Scott Marlowe" <scott.marlowe@gmail.com>) |
Responses |
Re: Index not being used
("Scott Marlowe" <scott.marlowe@gmail.com>)
Re: Index not being used ("Scott Marlowe" <scott.marlowe@gmail.com>) Re: Index not being used ("Scott Marlowe" <scott.marlowe@gmail.com>) |
List | pgsql-general |
On Aug 13, 2007, at 4:39 PM, Scott Marlowe wrote:
On 8/13/07, Ralph Smith <smithrn@u.washington.edu> wrote:I'm confused. Shouldn't this index be used?(It's running on v7.4.7)airburst=> \d stats2Table "public.stats2"Column | Type | Modifiers-----------+-----------------------+-----------lab | character varying(30) |name | character varying(50) |status | character varying(40) |eventtime | integer |username | character varying(30) |pkey | character varying(60) |Indexes:"stats2_etime_index" btree (eventtime)airburst=> \d stats2_etime_indexIndex "public.stats2_etime_index"Column | Type-----------+---------eventtime | integerbtree, for table "public.stats2"airburst=> explain select count(*) from stats2 where eventtime > 1167638400;QUERY PLAN-----------------------------------------------------------------------Aggregate (cost=185247.97..185247.97 rows=1 width=0)-> Seq Scan on stats2 (cost=0.00..179622.45 rows=2250205 width=0)Filter: (eventtime > 1167638400)(3 rows)
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=====================================================================That really depends. how many rows are actually returned? If it's2250205 like the query planner thinks, and that's a fair chunk of thetable, then no, it shouldn't use an index, a seq scan will be faster.What does explain analyze select ... say?
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Somewhere between 40,000 and 48,000 rows returned the index kicks in.
Out of a table of 7 million rows, that's a fairly common count I have to work with.
It's the amount of activity since August 2nd, this year; NOT that long ago.
Any suggestions on speeding up these queries, other than using more and more tables, thus ruling out the reasonable use of command-line queries?
Ultimately we'll move to some datawarehousing solution, but that's not a 'tomorrow' kind of thing...
Thanks again all,
Ralph
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