From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Jeevan Ladhe <jeevan(dot)ladhe(at)enterprisedb(dot)com>, PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Binary search in fmgr_isbuiltin() is a bottleneck. |
Date: | 2017-10-04 07:33:17 |
Message-ID: | 20171004073317.i64ildbyqb7a3t4m@alap3.anarazel.de |
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Lists: | pgsql-hackers |
On 2017-10-02 15:01:36 -0700, Andres Freund wrote:
> On 2017-10-02 17:57:51 -0400, Tom Lane wrote:
> > Andres Freund <andres(at)anarazel(dot)de> writes:
> > > Done that way. It's a bit annoying, because we've to take care to
> > > initialize the "unused" part of the array with a valid signalling it's
> > > an unused mapping. Can't use 0 for that because fmgr_builtins[0] is a
> > > valid entry.
> >
> > The prototype code I posted further upthread just used -1 as the "unused"
> > marker. There's no reason the array can't be int16 rather than uint16,
> > and "if (index < 0)" is probably a faster test anyway.
>
> Right, but whether we use -1 or UINT16_MAX or such doesn't matter. The
> relevant bit is that we can't use 0, so we can't rely on the rest of the
> array being zero initialized, but instead of to initialize all of it
> explicitly. I've no real feelings about using -1 or UINT16_MAX - I'd be
> very surprised if there's any sort of meaningful performance difference.
I pushed a further cleaned up version of these two patches. If you see
a way to avoid initializing the "trailing" part of the
fmgr_builtin_oid_index in a different manner, I'm all ears ;)
Greetings,
Andres Freund
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