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Re: User concurrency thresholding: where do I look?

From: "Simon Riggs" <simon(at)2ndquadrant(dot)com>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Jignesh K(dot) Shah" <J(dot)K(dot)Shah(at)Sun(dot)COM>,"Josh Berkus" <josh(at)agliodbs(dot)com>,<pgsql-performance(at)postgresql(dot)org>,"Alvaro Herrera" <alvherre(at)commandprompt(dot)com>
Subject: Re: User concurrency thresholding: where do I look?
Date: 2007-07-23 18:30:48
Message-ID: 1185215448.4284.295.camel@ebony.site (view raw or flat)
Thread:
Lists: pgsql-performance
On Mon, 2007-07-23 at 14:19 -0400, Tom Lane wrote:
> "Simon Riggs" <simon(at)2ndquadrant(dot)com> writes:
> > currPos and markPos are defined as BTScanPosData, which is an array of
> > BTScanPosItems. That makes BTScanOpaqueData up to 8232 bytes, which
> > seems wasteful since markPos is only ever used during merge joins. Most
> > of that space isn't even used during merge joins either, we just do that
> > to slightly optimise the speed of the restore during merge joins.
> 
> Ah.  I was seeing it as 6600 bytes on HPPA and 6608 on x86_64, but
> I forgot that both of those architectures have MAXALIGN = 8.  On a
> MAXALIGN = 4 machine, MaxIndexTuplesPerPage will be significantly
> larger, leading to larger BTScanPosData.
> 
> Not sure it's worth fooling with, given that these days almost everyone
> who's seriously concerned about performance is probably using 64bit
> hardware.  One less malloc cycle per indexscan is never going to be a
> measurable savings anyway...

Oh sure, I was thinking to avoid Solaris' mutex by avoiding malloc()
completely.

-- 
  Simon Riggs
  EnterpriseDB  http://www.enterprisedb.com


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