On 15/09/11 17:53, Yang Zhang wrote:
I have a simple query that's been running for a while, which is fine,
but it seems to be running very slowly, which is a problem:
mydb=# explain select user_id from den where user_id not in (select
duid from user_mappings) and timestamp between '2009-04-01' and
'2010-04-01';
Do you have indexes on user_id and timestamp?
QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Seq Scan on den (cost=711.58..66062724212.74 rows=22634720 width=4)
Filter: (("timestamp">= '2009-04-01 00:00:00'::timestamp without
time zone) AND ("timestamp"<= '2010-04-01 00:00:00'::timestamp
without time zone) AND (NOT (SubPlan 1)))
SubPlan 1
-> Materialize (cost=711.58..1223.38 rows=36780 width=4)
-> Seq Scan on user_mappings (cost=0.00..530.80 rows=36780 width=4)
user_mappings is fairly small:
mydb=# select count(*) from user_mappings;
count
-------
36780
(1 row)
I know that `den` is large but things seem to be running much slower
than I'd expect. Nothing in the logs. Is there any way to inspect
what's going on? Hesitant to kill the query in case it's almost done,
though I doubt it (didn't have the foresight to expose this
information in the client process - wasn't expecting to run into
this). Thanks in advance.
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