Re: explain analyze rows=%.0f

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Simon Riggs <simon(at)2ndQuadrant(dot)com>, Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com>, Euler Taveira de Oliveira <euler(at)timbira(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: explain analyze rows=%.0f
Date: 2009-06-02 14:56:59
Message-ID: EB5874A8-865D-4B45-A69D-A1A05198BE8E@gmail.com
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...Robert

On Jun 2, 2009, at 10:38 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Jun 2, 2009, at 9:41 AM, Simon Riggs <simon(at)2ndQuadrant(dot)com>
>> wrote:
>>> You're right that the number of significant digits already exceeds
>>> the
>>> true accuracy of the computation. I think what Robert wants to see
>>> is
>>> the exact value used in the calc, so the estimates can be checked
>>> more
>>> thoroughly than is currently possible.
>
>> Bingo.
>
> Uh, the planner's estimate *is* an integer. What was under discussion
> (I thought) was showing some fractional digits in the case where
> EXPLAIN
> ANALYZE is outputting a measured row count that is an average over
> multiple loops, and therefore isn't necessarily an integer. In that
> case the measured value can be considered arbitrarily precise ---
> though
> I think in practice one or two fractional digits would be plenty.

We're in violent agreement here.

...Robert

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