On 2018-10-16 10:16:33 -0400, Tom Lane wrote:
> Andres Freund <and...@anarazel.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
>From 575a51d94fd4bef6914ba55b33ba96504f64d574 Mon Sep 17 00:00:00 2001
From: Andres Freund <and...@anarazel.de>
Date: Tue, 16 Oct 2018 13:05:52 -0700
Subject: [PATCH] Reorder FmgrBuiltin members, saving 25% in size.
That's worth it, as fmgr_builtins is frequently accessed, and as
fmgr_builtins is one of the biggest constant variables in a backend.
---
src/backend/utils/Gen_fmgrtab.pl | 2 +-
src/include/utils/fmgrtab.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/src/backend/utils/Gen_fmgrtab.pl b/src/backend/utils/Gen_fmgrtab.pl
index fa30436895b..ca282913552 100644
--- a/src/backend/utils/Gen_fmgrtab.pl
+++ b/src/backend/utils/Gen_fmgrtab.pl
@@ -230,7 +230,7 @@ my $fmgr_count = 0;
foreach my $s (sort { $a->{oid} <=> $b->{oid} } @fmgr)
{
print $tfh
- " { $s->{oid}, \"$s->{prosrc}\", $s->{nargs}, $bmap{$s->{strict}}, $bmap{$s->{retset}}, $s->{prosrc} }";
+ " { $s->{oid}, $s->{nargs}, $bmap{$s->{strict}}, $bmap{$s->{retset}}, \"$s->{prosrc}\", $s->{prosrc} }";
$fmgr_builtin_oid_index[ $s->{oid} ] = $fmgr_count++;
diff --git a/src/include/utils/fmgrtab.h b/src/include/utils/fmgrtab.h
index d8317eb3eac..8d89d66777b 100644
--- a/src/include/utils/fmgrtab.h
+++ b/src/include/utils/fmgrtab.h
@@ -25,10 +25,10 @@
typedef struct
{
Oid foid; /* OID of the function */
- const char *funcName; /* C name of the function */
short nargs; /* 0..FUNC_MAX_ARGS, or -1 if variable count */
bool strict; /* T if function is "strict" */
bool retset; /* T if function returns a set */
+ const char * const funcName; /* C name of the function */
PGFunction func; /* pointer to compiled function */
} FmgrBuiltin;
--
2.18.0.rc2.dirty
