| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Subplan result caching |
| Date: | 2018-05-25 14:26:24 |
| Message-ID: | CA+Tgmoa9SOnygHgooUsoMNhx8Fa=v07G0wfuVoO4KkcJVyf29g@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, May 23, 2018 at 12:51 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Ah. That would work, though it'd make the number of subquery executions
> even less predictable (since some logically-equal values would compare
> as physically unequal).
In most cases that seems fine. It might not be fine with the subquery
contains volatile functions, though. I think I'd be sad if I wrote a
query expecting random() to be executing 26000 times and it got
executed 11 times instead. But if the optimizer finds a way to
execute int4pl fewer times, that seems like a good thing.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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