On Aug 13, 2007, at 4:39 PM, Scott Marlowe wrote:
I'm confused. Shouldn't this index be used?
(It's running on v7.4.7)
airburst=> \d stats2
Table "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_index
Index "public.stats2_etime_index"
Column | Type
-----------+---------
eventtime | integer
btree, 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's
2250205 like the query planner thinks, and that's a fair chunk of the
table, 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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