R: R: Query plan on identical tables differs . Why ?

>>>-----Messaggio originale-----
>>>Da: Tom Lane [mailto:tgl@sss.pgh.pa.us]
>>>Inviato: giovedì 13 maggio 2004 17.01
>>>A: Fabio Panizzutti
>>>Cc: 'Shridhar Daithankar'; pgsql-performance@postgresql.org
>>>Oggetto: Re: R: [PERFORM] Query plan on identical tables
>>>differs . Why ?
>>>
>>>
>>>"Fabio Panizzutti" <panizzutti@interlogica.net> writes:
>>>> I don't understand why the planner chose a different query plan on
>>>> identical tables with same indexes .
>>>
>>>Different data statistics; not to mention different table
>>>sizes (the cost equations are not linear).
>>>
>>>Have you ANALYZEd (or VACUUM ANALYZEd) both tables recently?
>>>
>>>If the stats are up to date but still not doing the right
>>>thing, you might try increasing the statistics target for
>>>the larger table's tag_id column.  See ALTER TABLE SET STATISTICS.
>>>
>>>            regards, tom lane
>>>

All tables are vacumed and analyzed .
I try so set statistics to 1000 to tag_id columns with ALTER TABLE SET
STATISTIC, revacuum analyze ,  but the planner choose the same query
plan .
I'm trying now to change the indexes .

Thanks