| From: | Richard Guo <guofenglinux(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Pg Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: weird hash plan cost, starting with pg10 |
| Date: | 2020-04-14 01:50:39 |
| Message-ID: | CAMbWs4--CKO3PRrZGKbWLv-Hb3Ae-fB-rdpsva5sn6oAA3ncRQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Apr 13, 2020 at 9:53 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Richard Guo <guofenglinux(at)gmail(dot)com> writes:
> > At first I was wondering if we need to check whether HashState.hashtable
> > is not NULL in ExecShutdownHash() before we decide to allocate save
> > space for HashState.hinstrument. And then I convinced myself that that's
> > not necessary since HashState.hinstrument and HashState.hashtable cannot
> > be both NULL there.
>
> Even if the hashtable is null at that point, creating an all-zeroes
> hinstrument struct is harmless.
>
Correct. The only benefit we may get from checking if the hashtable is
null is to avoid an unnecessary palloc0 for hinstrument. But that case
cannot happen though.
Thanks
Richard
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