Message-ID: <00c801c74cb0$04a27820$2900000a@demo01>
From: "Virag Saksena" <virag@auptyma.com>
To: <pgsql-performance@postgresql.org>
References: <00aa01c74ca6$7392a160$2900000a@demo01>
	<6478.1171068303@sss.pgh.pa.us>
Subject: Re: Is there an equivalent for Oracle's user_tables.num_rows 
Date: Fri, 9 Feb 2007 17:08:47 -0800
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Thanks, that is exactly what I was looking for

I know that number of rows may not be the best indicator, but it is a 
heuristic that can be tracked
easily, causing analyze for the first x insert events, and then only doing 
it only when an insert event causes
total rows to exceed y % of the optimizer perceived rows

Other more accurate heuristics like relative distribution of columns would 
be harder to track in the application,
and I'd rather let the database do that by issuing the analyze

Regards,

Virag

----- Original Message ----- 
From: "Tom Lane" <tgl@sss.pgh.pa.us>
To: "Virag Saksena" <virag@auptyma.com>
Cc: <pgsql-performance@postgresql.org>
Sent: Friday, February 09, 2007 4:45 PM
Subject: Re: [PERFORM] Is there an equivalent for Oracle's 
user_tables.num_rows


> "Virag Saksena" <virag@auptyma.com> writes:
>> Does someone know of a way of telling what the optimizer believes the =
>> number of rows are ?
>
> You're looking in the wrong place; see pg_class.relpages and reltuples.
>
> But note that in recent releases neither one is taken as gospel.
> Instead the planner uses the current physical table size in place of
> relpages, and scales reltuples correspondingly.  So neither steady
> growth nor truncation create a need for re-ANALYZE; at least not as long
> as the other statistics don't change too much.
>
> regards, tom lane
>