Horton

Re: explain analyze rows=%.0f

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Simon Riggs <simon@2ndQuadrant.com>
Cc: Ron Mayer <rm_pg@cheapcomplexdevices.com>, Euler Taveira de Oliveira <euler@timbira.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2009-06-02T14:06:18Z
Lists: pgsql-hackers 
On Jun 2, 2009, at 9:41 AM, Simon Riggs <simon@2ndQuadrant.com> wrote:

>
> On Mon, 2009-06-01 at 20:30 -0700, Ron Mayer wrote:
>
>> What I'd find strange about "6.67 rows" in your example is more  
>> that on
>> the estimated rows side, it seems to imply an unrealistically  
>> precise estimate
>> in the same way that "667 rows" would seem unrealistically precise  
>> to me.
>> Maybe rounding to 2 significant digits would reduce confusion?
>
> 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.

...Robert

Commits

  1. EXPLAIN: Always use two fractional digits for row counts.

  2. Adjust EXPLAIN test case to filter out "Actual Rows" values.

  3. Allow EXPLAIN to indicate fractional rows.

  4. Fix pgbench performance issue induced by commit af35fe501.