Re: Align large shared memory allocations

Manfred Spraul <manfred@colorfullife.com> writes:
> Tom Lane wrote:
>> This patch is missing a demonstration that it's actually worth anything.
>> What kind of performance gain do you get?
>>
> 7.4cvs on a 1.13 GHz Intel Celeron mobile, 384 MB RAM, "Severn" RedHat
> Linux 2.4 beta, postmaster -N 30 -B 64, data directory on ramdisk,
> pgbench -c 10 -s 11 -t 1000:
> Without the patch: 124 tps
> with the patch: 130 tps.

I tried it on an Intel box here (P4 I think).  Using postmaster -B 64 -N 30
and three tries of pgbench -s 10 -c 1 -t 1000 after creation of the test
tables, I get:

tps = 92.461144 (including connections establishing)
tps = 92.500572 (excluding connections establishing)

tps = 88.078814 (including connections establishing)
tps = 88.115905 (excluding connections establishing)

tps = 85.434473 (including connections establishing)
tps = 85.468807 (excluding connections establishing)

and with the patch:

tps = 122.927066 (including connections establishing)
tps = 122.998129 (excluding connections establishing)

tps = 110.716370 (including connections establishing)
tps = 110.773928 (excluding connections establishing)

tps = 138.155991 (including connections establishing)
tps = 138.245777 (excluding connections establishing)

So there's definitely a visible difference on recent Pentiums.  It might
not help on other CPUs, but we can surely waste a couple dozen bytes in
the hope that it might.

Patch applied.  Do you want to look at making it happen for local
buffers and buffile.c as well?

            regards, tom lane