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Re: getting to beta

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Robert Haas" <robertmhaas(at)gmail(dot)com>, <pgsql-hackers(at)postgresql(dot)org>
Cc: "Dan Ports" <drkp(at)csail(dot)mit(dot)edu>
Subject: Re: getting to beta
Date: 2011-04-21 16:32:03
Message-ID: 4DB015B3020000250003CB51@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-hackers
Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
 
> 1. All of the SSI patches have been dealt with.
 
I'll add the non-serializable UPDATE performance issue.  Dan has
been benchmarking to try to find a worst case; I don't want to speak
for him too much, but as he was headed off to lecture a class he
sent me results so far, and with beta so close I figure I should
pass along a rough outline.  The worst case he has been able to
construct so far was running 32 active processes on a 16 processor
machine in an update-mostly mix against a database on tmpfs (so no
disk writes) on a dataset which fits inside shared_memory.  This was
able to generate enough contention on an exclusive LW lock to cause
a 0.7% slowdown.
 
Speaking for myself, I believe we'll be able to provide a very small
patch to eliminate this.  Probably today or tomorrow.  While in a
less extreme runtime environment it would probably be hard to pick
out a performance impact in the normal noise, I expect the fix to be
small and safe enough to be worth doing.
 
I do feel that it would be good to apply the one-line fix Heikki
posted, which is orthogonal and needed in any event.  That would
give a little time for others to easily test it before beta.
 
-Kevin

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