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Re: questions about a table's row estimates - Mailing list pgsql-general

From Greg Smith
Subject Re: questions about a table's row estimates
Date
Msg-id 4B73A37A.4010906@2ndquadrant.com
Whole thread Raw
In response to questions about a table's row estimates  (Ben Chobot <bench@silentmedia.com>)
Responses Re: questions about a table's row estimates  (Tom Lane <tgl@sss.pgh.pa.us>)
Re: questions about a table's row estimates  (Ben Chobot <bench@silentmedia.com>)
List pgsql-general
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Ben Chobot wrote:
> I'm looking at pg_stat_user_tables in 8.4.2, and I'm confused about n_live_tup. Shouldn't that be at least fairly
closeto (n_tup_ins - n_tup-del)? It doesn't seem to be, but I'm unclear why. 
>
Insert 2000 tuples.
Delete 1000 tuples.
vacuum
Insert 1000 tuples. These go into the free space the deleted tuples used
to be in.
analyze

n_tup_ins=3000
n_tup_del=1000
n_live_tup=3000

If there's any delete/vacuum/reuse churn here, no reason the believe the
insert/delete and live counts will be close at all.

--
Greg Smith    2ndQuadrant   Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com  www.2ndQuadrant.com

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