Re: explain analyze rows=%.0f

On Thu, Jun 23, 2022 at 12:01 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.
>
> regards, tom lane
>
>
> Hi,
I was looking at the TODO list and found that the issue requires
a quick fix. Attached is a patch which shows output like this. It shows the
fraction digits in case of loops > 1

postgres=# explain analyze select * from foo;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------
Seq Scan on foo (cost=0.00..64414.79 rows=2326379 width=8) (actual
time=0.025..277.096 rows=2344671 loops=1
Planning Time: 0.516 ms
Execution Time: 356.993 ms
(3 rows)

postgres=# explain analyze select * from foo where b = (select c from
bar where c = 1);
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------
Seq Scan on foo (cost=8094.37..78325.11 rows=2326379 width=8)
(actual time=72.352..519.159 rows=2344671 loops=1
Filter: (b = $1)
InitPlan 1 (returns $1)
-> Gather (cost=1000.00..8094.37 rows=1 width=4) (actual
time=0.872..72.434 rows=1 loops=1
Workers Planned: 2
Workers Launched: 2
-> Parallel Seq Scan on bar (cost=0.00..7094.27 rows=1
width=4) (actual time=41.931..65.382 rows=0.33 loops=3)
Filter: (c = 1)
Rows Removed by Filter: 245457
Planning Time: 0.277 ms
Execution Time: 597.795 ms
(11 rows)

--
Ibrar Ahmed