Hi Andy,
Yeah sorry about the long name, there are all generated by function as part of
a table versioning system. And yes I placed all possible indexes on the table
to see which would be used by the planner. In production I will drop the unused
indexes.
Yes simple drop the extra index :P I have dropped the index and it made the
query slower :(
Here is the explain analyse:
Subquery Scan t (cost=170692.25..175678.27 rows=767 width=205) (actual
time=13762.783..14322.315 rows=106299 loops=1)'
Filter: (t.row_number = 1)'
-> WindowAgg (cost=170692.25..173760.57 rows=153416 width=86) (actual
time=13762.774..14208.522 rows=149557 loops=1)'
-> Sort (cost=170692.25..171075.79 rows=153416 width=86) (actual
time=13762.745..13828.584 rows=149557 loops=1)'
Sort Key: version_crs_coordinate_revision.id,
version_crs_coordinate_revision._revision_created'
Sort Method: quicksort Memory: 23960kB
-> Bitmap Heap Scan on version_crs_coordinate_revision
(cost=3319.13..157477.69 rows=153416 width=86) (actual time=70.925..13531.720
rows=149557 loops=1)
Recheck Cond: (((_revision_expired > 16) AND
(_revision_expired <= 40)) OR ((_revision_created > 16) AND (_revision_created
<= 40)))
Filter: (((_revision_created <= 16) AND (_revision_expired
> 16) AND (_revision_expired <= 40)) OR ((_revision_created > 16) AND
(_revision_created <= 40)))
-> BitmapOr (cost=3319.13..3319.13 rows=154372 width=0)
(actual time=53.650..53.650 rows=0 loops=1)
-> Bitmap Index Scan on
idx_crs_coordinate_revision_expired (cost=0.00..2331.76 rows=111041 width=0)
(actual time=37.773..37.773 rows=110326 loops=1)
Index Cond: ((_revision_expired > 16) AND
(_revision_expired <= 40))
-> Bitmap Index Scan on
idx_crs_coordinate_revision_created (cost=0.00..910.66 rows=43331 width=0)
(actual time=15.872..15.872 rows=43258 loops=1)
Index Cond: ((_revision_created > 16) AND
(_revision_created <= 40))
Total runtime: 14359.747 ms
http://explain.depesz.com/s/qpL says that the bitmap heap scan is bad. Not sure
what to do about it.
Thanks,
Jeremy
-----Original Message-----
From: Andy Colson [mailto:a...@squeakycode.net]
Sent: Monday, 17 January 2011 5:22 p.m.
To: Jeremy Palmer
Cc: pgsql-performance@postgresql.org
Subject: Re: [PERFORM] Possible to improve query plan?
First, wow, those are long names... I had a hard time keeping track.
Second: you have lots of duplicated indexes. I count _revision_created in 4
indexes? Not sure what other sql you are using, but have you tried one index
for one column? PG will be able to Bitmap them together if it thinks it can
use more than one. Was that because you were testing?
Third: any chance we can get an "explain analyze"? It give's more info.
(Also, have you seen http://explain.depesz.com/)
Last: If you wanted to force the index usage, for a test, you could drop the
other indexes. I assume this is on a test box so it should be ok. If its
live, you could wrap it in a BEGIN ... ROLLBACK (in theory... never tried it
myself)
-Andy
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