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Re: Postgresql 8.3 statistic stadistinct value dead wrong even with default_statistics_target=1000

From: Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Maxim Boguk <mboguk(at)masterhost(dot)ru>, pgsql-general(at)postgresql(dot)org
Subject: Re: Postgresql 8.3 statistic stadistinct value dead wrong even with default_statistics_target=1000
Date: 2008-08-30 03:08:03
Message-ID: 48B8B993.7040704@cheapcomplexdevices.com (view raw or flat)
Thread:
Lists: pgsql-general
Tom Lane wrote:
> Maxim Boguk <mboguk(at)masterhost(dot)ru> writes:
>> [ ndistinct estimates way off ]
> 
> Estimating the number of distinct values in a distribution with a long
> tail is just a really hard problem :-(

If I have a table where I know it has this property, is there
any way I can tell autovacuum's ANALYZE to go ahead and scan
the whole table?    ISTM a vacuum_cost_delay throttled full
table scan might be less harmful then a bad ndistinct guess.


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