Re: Discarding the resulting rows - Mailing list pgsql-hackers

<table border="0" cellpadding="0" cellspacing="0"><tr><td style="font: inherit;" valign="top"><br /><br />Hello All:<br
/><br/>The optimizer assumes that data is disk resident when computing the cost of a query plan.<br />I am trying to
ascertainwhat the correlation is between times and costs of some benchmark queries to see how good the cost model
is.<br/><br />Since I have more than 100 queries, it would be painful to stop and start the server each time to force
allthe buffer pages out. Also, some of these queries have large number of result rows. I don't want the time to be
skewedby the output time.<br /><br />Cheers,<br /><br />Murali.<br /><br /><br /><br
/>-----------------------------------------------------------------<br/>Please visit <a href="http://NumberFest.com"
rel="nofollow"target="_blank">NumberFest.com</a> for educational number puzzles & mind exercises for all ages! And
pleasetell your friends about it. Thank You!<br /><br /><br />--- On <b>Mon, 4/26/10, Tom Lane
<i><tgl@sss.pgh.pa.us></i></b>wrote:<br /><blockquote style="border-left: 2px solid rgb(16, 16, 255);
margin-left:5px; padding-left: 5px;"><br />From: Tom Lane <tgl@sss.pgh.pa.us><br />Subject: Re: [HACKERS]
Discardingthe resulting rows<br />To: "Jaime Casanova" <jcasanov@systemguards.com.ec><br />Cc: "Robert Haas"
<robertmhaas@gmail.com>,"Kevin Grittner" <Kevin.Grittner@wicourts.gov>, pgsql-hackers@postgresql.org,
"MuraliM. Krishna" <murali1729@yahoo.com><br />Date: Monday, April 26, 2010, 1:25 PM<br /><br /><div
class="plainMail">JaimeCasanova <<a href="/mc/compose?to=jcasanov@systemguards.com.ec"
ymailto="mailto:jcasanov@systemguards.com.ec">jcasanov@systemguards.com.ec</a>>writes:<br />> On Mon, Apr 26,
2010at 3:03 PM, Robert Haas <<a href="/mc/compose?to=robertmhaas@gmail.com"
ymailto="mailto:robertmhaas@gmail.com">robertmhaas@gmail.com</a>>wrote:<br />>> On Mon, Apr 26, 2010 at 3:36
PM,Kevin Grittner<br />>> <<a href="/mc/compose?to=Kevin.Grittner@wicourts.gov"
ymailto="mailto:Kevin.Grittner@wicourts.gov">Kevin.Grittner@wicourts.gov</a>>wrote:<br />>>> I would use
EXPLAINANALYZE SELECT ...<br />>> <br />>> There's some overhead to that, of course.<br /><br />> he
couldsee the "actual time" in the very first row of the EXPLAIN<br />> ANALYZE... isn't that a value that is more
closeto what the OP is<br />> looking for?<br /><br />Well, it will include the instrumentation overhead of EXPLAIN
ANALYZE,<br/>which can be nontrivial depending on your hardware and the query plan.<br /><br />On the other hand,
EXPLAINskips the cost of converting the result data<br />to text form, not to mention the network overhead of
deliveringit; so<br />in another sense it's underestimating the work involved.<br /><br />I guess the real question is
exactlywhat the OP is hoping to measure<br />and why.<br /><br />            regards, tom lane<br /><br />-- <br />Sent
viapgsql-hackers mailing list (<a href="/mc/compose?to=pgsql-hackers@postgresql.org"
ymailto="mailto:pgsql-hackers@postgresql.org">pgsql-hackers@postgresql.org</a>)<br/>To make changes to your
subscription:<br/><a href="http://www.postgresql.org/mailpref/pgsql-hackers"
target="_blank">http://www.postgresql.org/mailpref/pgsql-hackers</a><br/></div></blockquote></td></tr></table><br />