From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-hackers(at)postgresql(dot)org, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com> |
Subject: | Re: Large writable variables |
Date: | 2018-10-16 20:11:45 |
Message-ID: | 20181016201145.aa2dfeq54rhqzron@alap3.anarazel.de |
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Lists: | pgsql-hackers |
On 2018-10-16 10:16:33 -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > On 2018-10-16 01:59:00 -0400, Tom Lane wrote:
> >> Also, I noticed that the biggest part of those structs are arrays of
> >> FormatNode, which has been designed with complete lack of thought about
> >> size or padding issues. We can very easily cut it in half on 64-bit
> >> machines.
>
> > Heh, neat. I feel like we've paid very little attention to that in a
> > myriad of places :(
>
> Most of the time, we probably *shouldn't* pay attention to it; logical
> field ordering is worth a good deal IMO.
Sure. But there's plenty structs which we allocate a bunch off, that are
frequently accessed, where a lot of space is wasted to padding. I agree
that we don't need to contort many structs, but there's plenty where we
should. Often enough it's possible to reorder without making things
make meaningfully less sense.
> But in a case like this,
> where there are large arrays of the things and it's not very painful
> to avoid padding waste, it's worth the trouble.
Attached is a patch that shrinks fmgr_builtins by 25%. That seems
worthwhile, it's pretty frequently accessed, making it more dense is
helpful. Unless somebody protests soon, I'm going to apply that...
Greetings,
Andres Freund
Attachment | Content-Type | Size |
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0001-Reorder-FmgrBuiltin-members-saving-25-in-size.patch | text/x-diff | 1.7 KB |
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