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Re: Sort time

From: Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com>
To: pginfo <pginfo(at)t1(dot)unisoftbg(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, <josh(at)agliodbs(dot)com>,Rod Taylor <rbt(at)rbt(dot)ca>, "scott(dot)marlowe" <scott(dot)marlowe(at)ihs(dot)com>,"pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Sort time
Date: 2002-11-17 07:44:38
Message-ID: 20021116233532.J33150-100000@megazone23.bigpanda.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Sun, 17 Nov 2002, pginfo wrote:

> Hi,
>
> Stephan Szabo wrote:
>
> > On Sat, 16 Nov 2002, pginfo wrote:
> >
> > > Hi,
> > >
> > > Tom Lane wrote:
> > >
> > > > Josh Berkus <josh(at)agliodbs(dot)com> writes:
> > > > > Here's a question: is the total size of the column a good indicator of the
> > > > > sort_mem required?   Or does the rowsize affect it somehow?
> > > >
> > > > It will include all the data that's supposed to be output by the sort...
> > > > both the key column(s) and the others.
> > > >
> > >
> > > Hmm it is not clear for me.Let we have all data.
> > > If I make sort by S.OP ( it is INT) it take < 6 sek for sort.
> > > I think we move all this data anly the number of comparation is by INT. I think
> > > the number of comparation
> > > is ~ n * ln(n).
> > > If we sort by S.IDS_xxx we have also n*ln(n) comparations but in
> > > varchar(string).
> > > I don't think that it can take 50 sek.
> > >
> > > Is it not so?
> >
> > Have you tried setting up another database in "C" locale and compared the
> > timings there?  I'd wonder if maybe there's some extra copying going on
> > given the comments in varstr_cmp.
>
> No, I do not have any info about it.I will see if it is possible ( the data are not
> so simple).
> If it is possible I will make the tests.
> Have no one that have 700K row in thow tables?
> It is simple to test:
> 1. Run query that returns ~700K rows from this tables.
> 2. Make sort.
>
> It is interest only the sort time!

I can make a table of 700k rows and test it (and am generating 700k of
random varchar rows), but I wouldn't hold great hope that this is
necessarily a valid test since possibly any of OS, configuration settings
and actual data (width and values) might have an effect on the results.


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