public inbox for [email protected]
help / color / mirror / Atom feedFrom: David Rowley <[email protected]>
To: Robert Haas <[email protected]>
Cc: Ilia Evdokimov <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: Lukas Fittl <[email protected]>
Cc: Daniel Gustafsson <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: Nikolay Samokhvalov <[email protected]>
Cc: Andrei Lepikhov <[email protected]>
Subject: Re: Add estimated hit ratio to Memoize in EXPLAIN to explain cost adjustment
Date: Wed, 16 Apr 2025 08:49:46 +1200
Message-ID: <CAApHDvoqHSX8OOLQy4Eu2_mz2MWMyHsoArnCy70zHuAV47ssnA@mail.gmail.com> (raw)
In-Reply-To: <CA+TgmoZjVQf1-y2yj2OPWuL-eF=+UNv_vTUm_-98wg+Djj-vdA@mail.gmail.com>
References: <CAP53Pky29GWAVVk3oBgKBDqhND0BRBN6yTPeguV_qSivFL5N_g@mail.gmail.com>
<[email protected]>
<CAApHDvoE5S5FkvEq+N3-J9LfaVUpWLOnczOYAOEvBMCY20=pdg@mail.gmail.com>
<[email protected]>
<CAApHDvr9kjuo0rX03Qm0cDP_tFNJ8crOtpRzbyS0Zwtg2BorRw@mail.gmail.com>
<[email protected]>
<CAP53Pky44MuEYPDFcqR+ogffnifbuXkAWi5TvjhHmpSdj88o8w@mail.gmail.com>
<[email protected]>
<CA+TgmoZ8qXiZmmn4P9Mk1cf2mjMMLFPOjSasCjuKSiHFcm-ncw@mail.gmail.com>
<[email protected]>
<[email protected]>
<[email protected]>
<[email protected]>
<CAApHDvpT0Y1BfYgeWz+PkKaLBEff1izYOAjNSibhBTNFEdqLtg@mail.gmail.com>
<CA+TgmobDHmaNTqi5yLPJoW6fTCuiWOgF9CSCSHX_OTLmGxYRUQ@mail.gmail.com>
<CAApHDvqYL3OVvOsyvEPsDJ7h4zQh=LEygQgcQSN-TemRJLMb6Q@mail.gmail.com>
<[email protected]>
<CAApHDvpuM8jW-BGu7B=i6uv+jmndEo-2z_BYvj5JNmx=qV-uSQ@mail.gmail.com>
<CA+TgmoZjVQf1-y2yj2OPWuL-eF=+UNv_vTUm_-98wg+Djj-vdA@mail.gmail.com>
On Wed, 16 Apr 2025 at 04:25, Robert Haas <[email protected]> wrote:
>
> On Mon, Apr 14, 2025 at 8:23 PM David Rowley <[email protected]> wrote:
> > "Estimates: capacity=N distinct keys=N lookups=N hit ratio=N.N%"
>
> Is lookups=N here the estimated number of lookups i.e. what we think
> nloops will end up being?
Yes. The estimate is the "calls" variable in cost_memoize_rescan(),
which is fairly critical in the hit ratio estimate calculation.
Technically this is just the Nested Loop's outer_path->rows. There was
an argument earlier in the thread for putting this in along with the
other fields to make things easier to read. I did argue that it was
redundant due to the fact that the reader can look at the row estimate
for the outer side of the Nest Loop, but maybe it's small enough to go
in using the above format.
David
view thread (30+ messages) latest in thread
reply
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: [email protected]
Cc: [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected]
Subject: Re: Add estimated hit ratio to Memoize in EXPLAIN to explain cost adjustment
In-Reply-To: <CAApHDvoqHSX8OOLQy4Eu2_mz2MWMyHsoArnCy70zHuAV47ssnA@mail.gmail.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox