Edit report at https://bugs.php.net/bug.php?id=61060&edit=1
ID: 61060
Updated by: ras...@php.net
Reported by: trusty_jim at hotmail dot com
Summary: MySQL memory leak
-Status: Open
+Status: Not a bug
Type: Bug
Package: MySQL related
Operating System: Windows Vista
PHP Version: 5.3.10
Block user comment: N
Private report: N
New Comment:
This will depend on your mysql client library, and it isn't actually a memory
leak.
Running your script on my Ubuntu box gives me:
Start Memory : 227784
228240
228240
228240
228240
228240
228240
228240
228240
228240
228240
End Memory : 228120
On both PHP 5.3.11 and PHP 5.4.1 using the old outdated mysql extension built
against libmysqlclient-dev-5.1.61-0ubuntu0.11.10.1
Now, if however you are using the mysqlnd library, keep in mind that this
library uses PHP native memory management system, so anything allocated by the
library shows up in memory_get_usage(). So, using mysqli linked against mysqlnd
I get:
Start Memory : 235440
9969808
9970720
9971632
9972544
9973456
9974368
9975280
9976192
9977104
9978016
End Memory : 295280
But this makes perfect sense. Each time you fetch a row from the MySQL server
the client library needs to allocate memory to store that row. This happens in
the non-mysqlnd case as well, but it uses a straight system malloc() call so
the
memory doesn't show up when you call memory_get_usage(). It is still eating
memory, and it isn't actually a leak, that's how the library works. You get
your
memory back when you free the result.
Now, what this bug report is really asking is how do we tell the client library
not to buffer rows as we read them from the server. That's what unbuffered
queries are all about. In mysqli this see the use_result() method. For the old
deprecated mysql extension, see the mysql_unbuffered_query() function.
So, this is not actually a bug.
Previous Comments:
------------------------------------------------------------------------
[2012-04-10 16:59:23] jim at bladehq dot com
I have experienced this issue too. It appears to only leak memory when the
query is SELECT *. This has caused our application to run out of memory when
iterating over large result sets.
------------------------------------------------------------------------
[2012-02-12 03:50:28] trusty_jim at hotmail dot com
Description:
------------
Fetching data through mysql_fetch_assoc() causes php memory usage to go up
after
each query.
This occurs even after unsetting the retrieved data.
Test script:
---------------
<?php
$db = mysql_connect(DB_DOMAIN, DB_USERNAME, DB_PASS, true);
echo "Start Memory : ".memory_get_usage()."\n";
$result = mysql_query('SELECT * FROM addr', $db);
for ($i = 0; $i < 10; $i++) {
$row = mysql_fetch_assoc($result);
if ($row === false) break;
unset($row);
gc_collect_cycles();
echo " ".memory_get_usage()."\n";
}
mysql_free_result($result);
echo "End Memory : ".memory_get_usage()."\n";
?>
Expected result:
----------------
Memory usage should be similar after each execution
Start Memory : 31108008
65407576
65407576
65407576
65407576
65407576
65407576
65407576
65407576
65407576
65407576
End Memory : 31108160
Actual result:
--------------
Memory usage increases significantly after each execution
Start Memory : 31108008
65407576
65408120
65408664
65409208
65409752
65410296
65410840
65411384
65411944
65412488
End Memory : 31108160
------------------------------------------------------------------------
--
Edit this bug report at https://bugs.php.net/bug.php?id=61060&edit=1
