Re: [HACKERS] \dt and disk access

On Sat, 21 Jun 1997, Bruce Momjian wrote:

> > ExecSort calls psort() to do the work. psort() uses a Knuth algorithm.
> >
> > I removed the psort() call from ExecSort, and the execution time was:
> >
> >     Select with order by using psort():        0.30
> >
> >     Select with order by NOT using psort():        0.07
> >
> > Now of course, not using psort() causes the data not to be sorted, but
> > there must be some inefficienty if sorting one row takes 0.23 seconds on
> > a PP200 with 64MB of RAM.  I suspect the other 0.06 seconds is caused by
> > the creation of the temp table and moving the rows around.
>
> It looks like psort()'s use of disk files to do the sorting is causing
> the slowdown, with the multiple create's and unlink's.  I am going to
> modify psort() to use memory buffers instead of disk files for sorting
> small SELECT results.  psort() is only called by ExecSort, which is used
> by ORDER BY's.
>
> Permission to put this in 6.1p1?

Can you make the size of the result set above which diskfiles will be used
configurable? That way ppl with loads of RAM can use huge buffers, and ppl
with little RAM can keep that RAM free for other processes.

Maarten

_____________________________________________________________________________
|     Maarten Boekhold, Faculty of Electrical Engineering TU Delft,   NL    |
|        M.Boekhold@et.tudelft.nl   boekhold@gopher.library.tudelft.nl      |
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