| From: | Jesse Zhang <sbjesse(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Denis Smirnov <sd(at)arenadata(dot)io>, Soumyadeep Chakraborty <sochakraborty(at)pivotal(dot)io> |
| Subject: | Re: Properly mark NULL returns in numeric aggregates |
| Date: | 2020-04-13 17:34:00 |
| Message-ID: | CAGf+fX5FwjBUjA7WahGvX-OcqhjKB6d072eNa7RiFZ+0tG31Qg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Apr 10, 2020 at 3:59 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> They can't be strict because the initial iteration needs to produce
> something from a null state and non-null input. nodeAgg's default
> behavior won't work for those because nodeAgg doesn't know how to
> copy a value of type "internal".
>
> regards, tom lane
Ah, I think I get it. A copy must happen because the input is likely in
a shorter-lived memory context than the state, but nodeAgg's default
behavior of copying a by-value datum won't really copy the object
pointed to by the pointer wrapped in the datum of "internal" type, so we
defer to the combine function. Am I right? Then it follows kinda
naturally that those combine functions have been sloppy on arrival since
commit 11c8669c0cc .
Cheers,
Jesse
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