Horton

Re: kqueue

Thomas Munro <thomas.munro@enterprisedb.com>

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From: Thomas Munro <thomas.munro@enterprisedb.com>
To: Keith Fiske <keith@omniti.com>
Cc: Matteo Beccati <php@beccati.com>, Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>, Heikki Linnakangas <hlinnaka@iki.fi>, Marko Tiikkaja <marko@joh.to>, Alvaro Herrera <alvherre@2ndquadrant.com>, Robert Haas <robertmhaas@gmail.com>, Pg Hackers <pgsql-hackers@postgresql.org>, Noah Misch <noah@leadboat.com>
Date: 2016-09-14T23:04:15Z
Lists: pgsql-hackers 
On Thu, Sep 15, 2016 at 10:48 AM, Keith Fiske <keith@omniti.com> wrote:
> Thomas Munro brought up in #postgresql on freenode needing someone to test a
> patch on a larger FreeBSD server. I've got a pretty decent machine (3.1Ghz
> Quad Core Xeon E3-1220V3, 16GB ECC RAM, ZFS mirror on WD Red HDD) so offered
> to give it a try.
>
> Bench setup was:
> pgbench -i -s 100 -d postgres
>
> I ran this against 96rc1 instead of HEAD like most of the others in this
> thread seem to have done. Not sure if that makes a difference and can re-run
> if needed.
> With higher concurrency, this seems to cause decreased performance. You can
> tell which of the runs is the kqueue patch by looking at the path to
> pgbench.

Thanks Keith.  So to summarise, you saw no change with 1 client, but
with 4 clients you saw a significant drop in performance (~93K TPS ->
~80K TPS), and a smaller drop for 64 clients (~72 TPS -> ~68K TPS).
These results seem to be a nail in the coffin for this patch for now.

Thanks to everyone who tested.  I might be back in a later commitfest
if I can figure out why and how to fix it.

-- 
Thomas Munro
http://www.enterprisedb.com

Commits

  1. Add kqueue(2) support to the WaitEventSet API.

  2. Add WL_EXIT_ON_PM_DEATH pseudo-event.

  3. Be conservative about alignment requirements of struct epoll_event.

  4. Make idle backends exit if the postmaster dies.