Message-ID: <4F0AFC85.5050908@tech.sdb.it>
Date: Mon, 09 Jan 2012 15:41:09 +0100
From: Silvio Brandani <silvio.brandani@tech.sdb.it>
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To: pgsql-admin@postgresql.org
Subject: problem on table statistics
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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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