From: Silvio Brandani <silvio.brandani@tech.sdb.it>
To: pgsql-admin@postgresql.org
Subject: problem on table statistics
Date: Mon, 09 Jan 2012 15:41:09 +0100
Message-ID: <4F0AFC85.5050908@tech.sdb.it> (raw)
In the last few hours we get a problem with following query in
Production database :
select * from "001".mov_con where number in ( select number from
"001".mov_con where abs(amount-total_amo)>0.1) ;
The correct plan should be
QUERY PLAN
-----------------------------------------------------------------------------------------------------
Nested Loop (cost=541763.01..584606.03 rows=1249640 width=360)
-> HashAggregate (cost=541763.01..541807.55 rows=4454 width=10)
-> Index Scan using mov_con_x9 on mov_con t2
(cost=0.00..538639.38 rows=1249452 width=10)
Filter: (abs((amount - total_amo)) > 0.1::double precision)
-> Index Scan using mov_con_pkey on mov_con t1 (cost=0.00..6.10
rows=281 width=360)
Index Cond: (t1.number = t2.number)
(6 rows)
instead we get the following WRONG one:
QUERY PLAN
-----------------------------------------------------------------------------------------------
Nested Loop IN Join (cost=0.00..52906.16 rows=117499 width=620)
-> Index Scan using mov_con_x10 on mov_con t1 (cost=0.00..52483.90
rows=352486 width=620)
-> Index Scan using mov_con_x10 on mov_con t2 (cost=0.00..0.72
rows=3 width=11)
Index Cond: (t2.number = t1.number)
Filter: (abs((t2.amount - t2.total_amo)) > 0.1::double precision)
So I go to see statistics and try to change the
default_statistics_target from 10 to 100 , reload the configuration and
vacuum the table and the result is that while
the other tables have now 100 values on pg_stats the mov_con table
still have the same values
SELECT * FROM pg_stats
WHERE tablename='mov_con' AND attname='number' ;
So there is something wrong with table statistics. How can I reset the
pg_statistics for this table???
Any comment higly appreciated.
--
Silvio Brandani
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To: pgsql-admin@postgresql.org
Cc: silvio.brandani@tech.sdb.it
Subject: Re: problem on table statistics
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