| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| 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 14:38:27 |
| Message-ID: | 11926.1243953507@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
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.
regards, tom lane
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