I have a query that needs to run faster, with the obvious solution being to add an index.
But to confirm this, I ran explain analyze. When I run the actual query, it
consistently takes 6-7 seconds by the wall clock. My application with a
"verbose" mode enabled reports 6.6 seconds consistently. However, when I run
EXPLAIN ANALYZE, it takes 120 seconds! This is 20x longer, and it leads me to distrust
the plan that it claims to be executing. How can the actual run time be so much faster
than that claimed by EXPLAIN ANALYZE? How can I find out the actual plan it's using?
Thanks,
Craig
Details:
Postgres 8.0.3
shared_buffers = 20000
work_mem = 500000
effective_cache_size = 430000
Dell w/ Xeon
Linux kernel 2.6.9-1.667smp
4 GB memory
=> explain analyze select SAMPLE.SAMPLE_ID,
SAMPLE.VERSION_ID,SAMPLE.SUPPLIER_ID,SAMPLE.CATALOGUE_ID,SAMPLE.PREP_ID from
HITLIST_ROWS_281430 join SAMPLE on (HITLIST_ROWS_281430.OBJECTID =
SAMPLE.SAMPLE_ID) where SAMPLE.VERSION_ID in
(7513672,7513650,7513634,7513620,7513592,7513590,7513582,7513576,7513562,7513560)
order by HITLIST_ROWS_281430.SortOrder;
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Sort (cost=234964.38..234964.52 rows=58 width=24) (actual
time=120510.842..120510.889 rows=10 loops=1)
Sort Key: hitlist_rows_281430.sortorder
-> Hash Join (cost=353.68..234962.68 rows=58 width=24) (actual
time=81433.194..120510.753 rows=10 loops=1)
Hash Cond: ("outer".objectid = "inner".sample_id)
-> Seq Scan on hitlist_rows_281430 (cost=0.00..177121.61
rows=11497361 width=8) (actual time=0.008..64434.110 rows=11497361 loops=1)
-> Hash (cost=353.48..353.48 rows=82 width=20) (actual
time=0.293..0.293 rows=0 loops=1)
-> Index Scan using i_sample_version_id, i_sample_version_id,
i_sample_version_id, i_sample_version_id, i_sample_version_id,
i_sample_version_id, i_sample_version_id, i_sample_version_id,
i_sample_version_id, i_sample_version_id on sample (cost=0.00..353.48 rows=82
width=20) (actual time=0.042..0.201 rows=12 loops=1)
Index Cond: ((version_id = 7513672) OR (version_id =
7513650) OR (version_id = 7513634) OR (version_id = 7513620) OR (version_id =
7513592) OR (version_id = 7513590) OR (version_id = 7513582) OR (version_id =
7513576) OR (version_id = 7513562) OR (version_id = 7513560))
Total runtime: 120511.485 ms
(9 rows)
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TIP 2: Don't 'kill -9' the postmaster
