#6608 [Com]: sizeof($array) extremly slow in loop. 90% cpu util
| From: | benji at daystream dot com | Date: | Sun, 02 Mar 2003 18:56:39 +0000 |
| Subject: | #6608 [Com]: sizeof($array) extremly slow in loop. 90% cpu util | ||
| References: | 1 | Groups: | php.bugs |
| Request: | Send a blank email to php-bugs+get-34632@lists.php.net to get a copy of this message | ||
ID: 6608
Comment by: benji at daystream dot com
Reported By: mledet at spirenet dot com
Status: Closed
Bug Type: Performance problem
Operating System: Linux 2.2.16
PHP Version: 4.0.2
New Comment:
Here's more of the code, previous to the loops:
$sentence="I acn run to the store adn sing without knowing why."
$num=0;
$num++; $spell[$num]=Array(" acn "," can ");
$num++; $spell[$num]=Array(" adn "," and ");
// there are about 800 of these types of corrections. I expect you dont
want me to include them all.
My tests today show a difference of .18 seconds to 3.4 seconds. That's
about 20X slower. Better for some reason, but still not optimal by a
long shot.
Previous Comments:
------------------------------------------------------------------------
[2003-03-01 13:07:11] gschlossnagle@php.net
I see about a 20% overhead in executing the two loops with
a no-op inside the loop. This amount of overhead is
expected (due to the fact that your are making an extra
function call on every iteration). Nowhere near 5000%.
Tested on OSX with this:
<?php
for($i=0;$i < 100000; $i++) {
$array[] = '1';
}
for($i=0; $i < sizeof($array); $i++) {
}
?>
vs.
<?php
for($i=0;$i < 100000; $i++) {
$array[] = '1';
}
$end = sizeof($array);
for($i=0; $i < $end; $i++) {
}
?>
Your code fragment is not complete, so I cant actually
repliate your test.
------------------------------------------------------------------------
[2003-03-01 12:50:59] benji at daystream dot com
Please reopen this issue. It still exists in version 4.3.0. I'm running
on OSX. The performance with a large array that uses sizeof() in a loop
is very poor. It's abut 50X slower than it should be.
The following takes 8-10 seconds:
for ($i=1;$i<=sizeof($spell);$i++) {
$sentence=str_replace($spell[$i][0],$spell[$i][1],$sentence);
}
Whereas the following takes only .18 seconds:
$end=sizeof($spell);
for ($i=1;$i<=$end;$i++) {
$sentence=str_replace($spell[$i][0],$spell[$i][1],$sentence);
}
------------------------------------------------------------------------
[2001-05-10 05:55:09] sniper@php.net
No feedback. I problem exists with 4.0.5, reopen.
------------------------------------------------------------------------
[2001-04-10 10:12:23] sbergmann@php.net
Could you please test your script with either the PHP 4.0.4pl1 release,
the latest PHP 4.0.5 RC or a current CVS snapshot from
http://snaps.php.net/? Thanks.
------------------------------------------------------------------------
[2000-09-07 13:01:24] mledet at spirenet dot com
The following code performed well under 3.0.16.
for ($i=0; $i < sizeof($teacherarray); $i++) {
$a=$teacher_array[$i];
if ($a->teacher_id==$teacher_id) {
break;
}
}
However, under php 4.0.2 it is extrememly slow and causes cpu util for
the httpd process to hit 90%. $teacherarray is not being modified
during the loop so the condition isn't changing.
BTW: Changing to the following code works ok.
$numteachers = sizeof($teacherarray);
for ($i=0; $i < $numteachers; $i++) {
$a=$teacher_array[$i];
if ($a->teacher_id==$teacher_id) {
break;
}
}
Either the sizeof function has had a serious decrease in its speed or
something is awry..
------------------------------------------------------------------------
--
Edit this bug report at http://bugs.php.net/?id=6608&edit=1