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Re: Posix Shared Mem patch

From: Daniel Farina <daniel(at)heroku(dot)com>
To: Merlin Moncure <mmoncure(at)gmail(dot)com>
Cc: Andres Freund <andres(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org, Josh Berkus <josh(at)agliodbs(dot)com>
Subject: Re: Posix Shared Mem patch
Date: 2012-06-29 23:03:40
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Lists: pgsql-hackers
On Fri, Jun 29, 2012 at 1:00 PM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
> On Fri, Jun 29, 2012 at 2:52 PM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
>> Hi All,
>> In a *very* quick patch I tested using huge pages/MAP_HUGETLB for the mmap'ed
>> memory.
>> That gives around 9.5% performance benefit in a read-only pgbench run (-n -S -
>> j 64 -c 64 -T 10 -M prepared, scale 200, 6GB s_b, 8 cores, 24GB mem).
>> It also saves a bunch of memory per process due to the smaller page table
>> (shared_buffers 6GB):
>> cat /proc/$pid_of_pg_backend/status |grep VmPTE
>> VmPTE:      6252 kB
>> vs
>> VmPTE:        60 kB
> ... those results are just spectacular (IMO). nice!

That is super awesome.  Smallish databases with a high number of
connections actually spend a considerable fraction of their
otherwise-available-for-buffer-cache space on page tables in common
cases currently.


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