| From: | Andrei Lepikhov <lepihov(at)gmail(dot)com> |
|---|---|
| To: | Ilia Evdokimov <ilya(dot)evdokimov(at)tantorlabs(dot)com>, Matheus Alcantara <matheusssilv97(at)gmail(dot)com> |
| Cc: | Guillaume Lelarge <guillaume(at)lelarge(dot)info>, Daniel Gustafsson <daniel(at)yesql(dot)se>, Ibrar Ahmed <ibrar(dot)ahmad(at)gmail(dot)com>, "Gregory Stark (as CFM)" <stark(dot)cfm(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Peter Geoghegan <pg(at)bowt(dot)ie>, vignesh C <vignesh21(at)gmail(dot)com>, "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Subject: | Re: explain analyze rows=%.0f |
| Date: | 2025-02-11 17:14:49 |
| Message-ID: | e75ab0ca-2e52-462d-8fcc-35f7d3e86877@gmail.com |
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| Lists: | pgsql-hackers |
On 8/2/2025 04:28, Ilia Evdokimov wrote:
> On 08.02.2025 00:01, Matheus Alcantara wrote:
>> Just for reference I'm trying to apply based on commit fb056564ec5.
> You are right, because two commits were appeared after creating v6-patch
> on partition_prune.out and patch v6 must not have applied on master.
> Then I created v7 patch rebased on fb056564ec5 . Thank for your remark!
I support the idea in general, but I believe it should be expanded to
cover all cases of parameterised plan nodes. Each rescan iteration may
produce a different number of tuples, and rounding can obscure important
data.
For example, consider five loops of a scan node: the first loop returns
nine tuples, and each other - zero tuples. When we calculate the
average, 9 divided by 5 equals 1.8. This results in an explanation that
indicates "rows = 1," masking almost 40% of the data.
Now, if we apply the same two loops but have a total of 900,000 tuples,
then 400,000 masked tuples represent a significant portion of the data.
Moreover, switching to a floating-point type for row explanations in
each parameterised node would provide a more comprehensive view and add
valuable information about the parameterisation of the node, which may
not be immediately apparent.
--
regards, Andrei Lepikhov
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