Re: Need help with phys backed shm segments (Postgresql+FreeBSD).

* Oleg Bartunov <oleg@sai.msu.su> [001205 13:33] wrote:
> Alfred,
> 
> do you have any numbers with and without your patch ?
> I mean performance. You may use pg_check utility.

Er, I just made the patch a couple of hours ago, and I'm also
dealing with some other FreeBSD issues right now.  I will report
on it as soon as I can.

Theoretically You'll only see performance gains when doing fork(),
the real intent here is to allow for giant segments, without
kern.ipc.shm_use_phys=1 running let's say 768meg (out of 1gig)
shared memory segments will probably cause performance problems
because of the amount of swap structures needed per-process to
manage swappable segments.

I'm going to be enabling this on one of our boxes and see if it
makes a noticeable difference.  I'll let you guys know.

> > Date: Tue, 5 Dec 2000 13:04:45 -0800
> > From: Alfred Perlstein <bright@wintelcom.net>
> > To: Tom Lane <tgl@sss.pgh.pa.us>
> > Cc: pgsql-hackers@postgresql.org
> > Subject: Re: [HACKERS] Need help with phys backed shm segments (Postgresql+FreeBSD).
> > 
> > Here's the patch I'm using on FreeBSD, it seems to work, if any
> > other FreeBSD'ers want to try it out, just apply the patch:
> > cd /usr/src/sys/vm ; patch < patchfile
> > 
> > and recompile and boot with a new kernel, then do this:
> > 
> > sysctl -w kern.ipc.shm_use_phys=1
> > 
> > or add:
> > kern.ipc.shm_use_phys=1 
> > to /etc/sysctl.conf
> > 
> > Let me know if it works.
> > 
> > thanks,
> > -Alfred