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Re: Storing hot members of PGPROC out of the band

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Jim Nasby <jim(at)nasby(dot)net>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Storing hot members of PGPROC out of the band
Date: 2011-12-17 14:00:39
Message-ID: (view raw or whole thread)
Lists: pgsql-hackers
On Sat, Dec 17, 2011 at 1:00 AM, Jim Nasby <jim(at)nasby(dot)net> wrote:
> I also wonder how much this throws some previous performance tests into suspicion. If it's not uncommon for performance improvement attempts to shift a bottleneck to a different part of the system and marginally hurt performance then we might be throwing away good performance improvement ideas before we should...

I think we are (mostly) OK on this point, at least as far as the work
I've been doing.  We've actually had a few previous instances of this
phenomenon - e.g. when I first committed my fastlock patch,
performance actually got worse if you had >40 cores doing read-only
queries, because speeding up the lock manager made it possible for the
spinlock protection SInvalReadLock to mess things up royally.
Nevertheless, we got it committed - and fixed the SInvalReadLock
problem, too.  This one is/was somewhat more subtle, but I'm feeling
pretty good about our chances of making at least some further progress
in time for 9.2.

Robert Haas
The Enterprise PostgreSQL Company

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