Re: performace problem after VACUUM ANALYZE

Tom,

Sorry about that:  I'll try to briefly give the information you are
looking for.  I've read the docs on ALTER TABLE, but it is not clear to
me what columns I should change STATISTICS on, or should I just do it on
all of the columns for which indexes exist?

Here's the query again:

select distinct f.name,fl.nbeg,fl.nend,fl.strand,f.type_id,f.feature_id
    from feature f, featureloc fl
    where
      fl.srcfeature_id = 1 and
      ((fl.strand=1  and fl.nbeg <= 393164 and fl.nend >= 390956) OR
      (fl.strand=-1 and fl.nend <= 393164 and fl.nbeg >= 390956)) and
      f.feature_id  = fl.feature_id

--------------------------------------------------------------------------

Naive database:

Unique  (cost=75513.46..75513.48 rows=1 width=167) (actual
time=22815.25..22815.93 rows=179 loops=1)
  ->  Sort  (cost=75513.46..75513.46 rows=1 width=167) (actual
time=22815.24..22815.43 rows=186 loops=1)
        ->  Nested Loop  (cost=0.00..75513.45 rows=1 width=167) (actual
time=2471.25..22814.01 rows=186 loops=1)
              ->  Index Scan using featureloc_idx2 on featureloc fl
(cost=0.00..75508.43 rows=1 width=14) (actual time=2463.83..22796.50
rows=186 loops=1)
              ->  Index Scan using feature_pkey on feature f
(cost=0.00..5.01 rows=1 width=153) (actual time=0.08..0.08 rows=1
loops=186)
Total runtime: 22816.63 msec
--------------------------------------------------------------------------

Naive database after featureloc_idx2 dropped:

Unique  (cost=75545.46..75545.48 rows=1 width=167) (actual
time=5232.36..5234.51 rows=179 loops=1)
  ->  Sort  (cost=75545.46..75545.46 rows=1 width=167) (actual
time=5232.35..5232.54 rows=186 loops=1)
        ->  Nested Loop  (cost=0.00..75545.45 rows=1 width=167) (actual
time=291.46..5220.69 rows=186 loops=1)
              ->  Index Scan using featureloc_src_strand_beg_end on
featureloc fl  (cost=0.00..75540.43 rows=1 width=14) (actual
time=291.30..5214.46 rows=186 loops=1)
              ->  Index Scan using feature_pkey on feature f
(cost=0.00..5.01 rows=1 width=153) (actual time=0.02..0.03 rows=1
loops=186)
Total runtime: 5234.89 msec
--------------------------------------------------------------------------

Database after VACUUM ANALYZE was run:

Unique  (cost=344377.70..344759.85 rows=2548 width=47) (actual
time=26466.82..26467.51 rows=179 loops=1)
  ->  Sort  (cost=344377.70..344377.70 rows=25477 width=47) (actual
time=26466.82..26467.01 rows=186 loops=1)
        ->  Nested Loop  (cost=0.00..342053.97 rows=25477 width=47)
(actual time=262.66..26465.63 rows=186 loops=1)
              ->  Seq Scan on featureloc fl  (cost=0.00..261709.31
rows=25477 width=14) (actual time=118.62..26006.05 rows=186 loops=1)
              ->  Index Scan using feature_pkey on feature f
(cost=0.00..3.14 rows=1 width=33) (actual time=2.45..2.46 rows=1
loops=186)
Total runtime: 26467.85 msec
--------------------------------------------------------------------------

After disallowing seqscans (set enable_seqscan=0):

Unique  (cost=356513.46..356895.61 rows=2548 width=47) (actual
time=27494.62..27495.34 rows=179 loops=1)
  ->  Sort  (cost=356513.46..356513.46 rows=25477 width=47) (actual
time=27494.61..27494.83 rows=186 loops=1)
        ->  Nested Loop  (cost=0.00..354189.73 rows=25477 width=47)
(actual time=198.88..27493.48 rows=186 loops=1)
              ->  Index Scan using featureloc_idx1 on featureloc fl
(cost=0.00..273845.08 rows=25477 width=14) (actual time=129.30..27280.95
rows=186 loops=1)
              ->  Index Scan using feature_pkey on feature f
(cost=0.00..3.14 rows=1 width=33) (actual time=1.13..1.13 rows=1
loops=186)
Total runtime: 27495.66 msec
--------------------------------------------------------------------------

After dropping featureloc_idx1:

Unique  (cost=1310195.21..1310577.36 rows=2548 width=47) (actual
time=21692.69..21693.37 rows=179 loops=1)
  ->  Sort  (cost=1310195.21..1310195.21 rows=25477 width=47) (actual
time=21692.69..21692.88 rows=186 loops=1)
        ->  Nested Loop  (cost=0.00..1307871.48 rows=25477 width=47)
(actual time=2197.65..21691.39 rows=186 loops=1)
              ->  Index Scan using featureloc_idx2 on featureloc fl
(cost=0.00..1227526.82 rows=25477 width=14) (actual
time=2197.49..21618.89 rows=186 loops=1)
              ->  Index Scan using feature_pkey on feature f
(cost=0.00..3.14 rows=1 width=33) (actual time=0.37..0.38 rows=1
loops=186)
Total runtime: 21693.72 msec
--------------------------------------------------------------------------

After dropping featureloc_idx2:

Unique  (cost=1414516.98..1414899.13 rows=2548 width=47) (actual
time=1669.17..1669.86 rows=179 loops=1)
  ->  Sort  (cost=1414516.98..1414516.98 rows=25477 width=47) (actual
time=1669.17..1669.36 rows=186 loops=1)
        ->  Nested Loop  (cost=0.00..1412193.25 rows=25477 width=47)
(actual time=122.69..1668.08 rows=186 loops=1)
              ->  Index Scan using featureloc_src_strand_beg_end on
featureloc fl  (cost=0.00..1331848.60 rows=25477 width=14) (actual
time=122.51..1661.81 rows=186 loops=1)
              ->  Index Scan using feature_pkey on feature f
(cost=0.00..3.14 rows=1 width=33) (actual time=0.02..0.03 rows=1
loops=186)
Total runtime: 1670.20 msec


On Fri, 2003-02-14 at 12:00, Tom Lane wrote:
> Scott Cain <cain@cshl.org> writes:
> > [ much stuff ]
>
> Could we see EXPLAIN ANALYZE, not just EXPLAIN, output for all these
> alternatives?  Your question boils down to "why is the planner
> misestimating these queries" ... which is a difficult question to
> answer when given only the estimates and not the reality.
>
> A suggestion though is that you might need to raise the statistics
> target on the indexed columns, so that ANALYZE will collect
> finer-grained statistics.  (See ALTER TABLE ... SET STATISTICS.)
> Try booting it up to 100 (from the default 10), re-analyze, and
> then see if/how the plans change.
>
>             regards, tom lane
--
------------------------------------------------------------------------
Scott Cain, Ph. D.                                         cain@cshl.org
GMOD Coordinator (http://www.gmod.org/)                     216-392-3087
Cold Spring Harbor Laboratory