"Mark Cave-Ayland" <m.cave-ayland@webbased.co.uk> writes:
> I'm trying to install a copy of PostgreSQL 7.3.8 on FC3 x86_64, and having a
> very strange problem with shared memory in that PostgreSQL seems to be
> taking far too many semaphores for the parameters in the postgresql.conf
> file.

Judging by the symptoms, you have built a version with what we now call
--disable-spinlocks; that is, it didn't figure out how to do assembly
TAS on your platform and fell back to using SysV semaphores for spinlocks.
Quite aside from the drain on semaphores, the performance is going to
be spectacularly bad, so you'd better fix that.

regards, tom lane

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> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
> Sent: 31 January 2005 16:35
> To: Mark Cave-Ayland
> Cc: pgsql-hackers@postgresql.org
> Subject: Re: [HACKERS] 7.3.8 under FC3 takes excessive semaphores?

(cut)

> Judging by the symptoms, you have built a version with what
> we now call --disable-spinlocks; that is, it didn't figure
> out how to do assembly TAS on your platform and fell back to
> using SysV semaphores for spinlocks. Quite aside from the
> drain on semaphores, the performance is going to be
> spectacularly bad, so you'd better fix that.
>
> regards, tom lane


Hi Tom,

I'd just about managed to come to the same conclusion before your email
arrived by spending the afternoon with gdb tracing into the LWLock code

I've just installed 7.4.6 on the same box and this time the spinlocks are
correctly picked up and everything works as expected. I think rather than
fixing the 7.3.x source, we'll take the plunge and plan for a complete dump
and restore of the database cluster over a weekend.


Many thanks,

Mark.

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Mark Cave-Ayland wrote:
>
> > -----Original Message-----
> > From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
> > Sent: 31 January 2005 16:35
> > To: Mark Cave-Ayland
> > Cc: pgsql-hackers@postgresql.org
> > Subject: Re: [HACKERS] 7.3.8 under FC3 takes excessive semaphores?
>
> (cut)
>
> > Judging by the symptoms, you have built a version with what
> > we now call --disable-spinlocks; that is, it didn't figure
> > out how to do assembly TAS on your platform and fell back to
> > using SysV semaphores for spinlocks. Quite aside from the
> > drain on semaphores, the performance is going to be
> > spectacularly bad, so you'd better fix that.
> >
> > regards, tom lane
>
>
> Hi Tom,
>
> I'd just about managed to come to the same conclusion before your email
> arrived by spending the afternoon with gdb tracing into the LWLock code
>
> I've just installed 7.4.6 on the same box and this time the spinlocks are
> correctly picked up and everything works as expected. I think rather than
> fixing the 7.3.x source, we'll take the plunge and plan for a complete dump
> and restore of the database cluster over a weekend.

And with 7.4 and later we will throw a configure error if we don't find
native spinlocks so you will have no surprises in the future.

--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073

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