Re: Performance of ORDER BY

Thanks to Luke and Tom for the input.  I guess this was good timing given that it looks like<br /> 8.2 was just
releasedtoday.   I will upgade to that before doing anything else.<br /><br /> Glenn<br /><br /> Tom Lane wrote:
<blockquotecite="mid7090.1165341726@sss.pgh.pa.us" type="cite"><pre wrap="">Glenn Sullivan <a
class="moz-txt-link-rfc2396E"href="mailto:glenn.sullivan@varianinc.com"><glenn.sullivan@varianinc.com></a>
writes:</pre><blockquote type="cite"><pre wrap="">I am wanting some ideas about improving the performance of ORDER BY
in
our use.  I have a DB on the order of 500,000 rows and 50 columns.
The results are always sorted with ORDER BY.  Sometimes, the users end up
with a search that matches most of the rows.  In that case, I have a
LIMIT 5000 to keep the returned results under control.  However, the
sorting seems to take 10-60 sec.  If I do the same search without the
ORDER BY, it takes about a second.     </pre></blockquote><pre wrap="">
Does the ORDER BY match an index?  If so, is it using the index?
(See EXPLAIN.)
 </pre><blockquote type="cite"><pre wrap="">I am currently on version 8.0.1 on Windows XP using a Dell Optiplex 280
with 1Gb of ram.  I have set sort_mem=100000 set.   </pre></blockquote><pre wrap="">
In 8.0 that might be counterproductively high --- we have seen cases
where more sort_mem = slower with the older sorting code.  I concur
with Luke's advice that you should update to 8.2 (not 8.1) to get the
improved sorting code.
        regards, tom lane
 </pre></blockquote>