Bug #48528 [Com]: mysqlnd causes PDO/MySQLi to leak memory

Edit report at https://bugs.php.net/bug.php?id=48528&edit=1 ID: 48528 Comment by: ben at ajmadison dot com Reported by: bugs dot php dot net at moesen dot nu Summary: mysqlnd causes PDO/MySQLi to leak memory Status: Closed Type: Bug Package: MySQL related Operating System: Linux 2.6 PHP Version: 5.3CVS-2009-06-11 (snap) Block user comment: N Private report: N New Comment: The answer is not 100% correct. It is true that libmysqlclient hides the amount of allocted memory, while mysqlnd shows up in PHP. Here are the results I obtained using the latest PHP 5.5.1 build. When measured by "ps aux|grep php|grep mysql" though, mysqlnd memory usage keeps climbing during loop iteration, getting to over 5 times the amount of memory allocated during mysql_query. libmysqlclient memory usage only goes up while mysql_query is running, and stays constant during iteration. Why does mysqlnd use so much more memory than lilbmysqlclient, as reported by: "ps aux|grep php|grep mysql"? Why does iterating throught he loop use 5 times+ the memory of mysql_query? Previous Comments: ------------------------------------------------------------------------ [2009-11-03 09:45:19] uw@php.net Duplicate of http://bugs.php.net/bug.php?id=48343 - there is no leak, mysqlnd and libmysql work differently. ------------------------------------------------------------------------ [2009-10-30 12:32:15] guenter at grodotzki dot ph same problem here, though with the normal mysql_query + mysql_fetch* functions ------------------------------------------------------------------------ [2009-06-20 01:00:00] php-bugs at lists dot php dot net No feedback was provided for this bug for over a week, so it is being suspended automatically. If you are able to provide the information that was originally requested, please do so and change the status of the bug back to "Open". ------------------------------------------------------------------------ [2009-06-16 08:31:16] bugs dot php dot net at moesen dot nu > libmysql's allocations are hidden. OK, that explains the numbers. Thanks. > Do you really get OOM with mysqlnd? Yes, for the same dataset. > as you can see the memory usage with USE_RESULT doesn't jump Thanks for that pointer. I completely missed it in the documentation, and since we never had any problems before switching over to 5.3, I never needed it. The human equivalent of lazy evaluation, I guess. So if I understand it correctly, libmysql is not subject to PHP's memory limit, whereas mysqlnd is? ------------------------------------------------------------------------ [2009-06-12 07:36:09] andrey@php.net Do you really get OOM with mysqlnd? memory_get_usage() is constant with libmysql because libmysql allocates its memory with malloc while Zend and all PHP functions mostly use emalloc. emalloc counts the allocated memory. libmysql's allocations are hidden. I tried your script, created a simple table with the same name and - int - double - varchar - decimal columns. I have 33 rows. Here is the output when the data is fetched with MYSQLI_STORE_RESULT, which is the default: 361756 <- before $result = $db->query 366384 366656 366928 367200 367472 367744 368016 368288 368560 368832 369104 369376 369648 369920 370192 370464 370736 371008 371280 371552 371824 372096 372368 372640 372912 373184 373456 373728 374000 374272 374544 374816 375088 362840 <- this is the result after I do $result->free_result(), which means that the memory doesn't leak. Most of it is reclaimed. It can be that Zend also cache some zvals in its zval cache, which means that memory has not leaked and is there for further usage. Here is with MYSQLI_USE_RESULT: 361756 <- before $result = $db->query 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 365764 362840 <- After $result->free_result() So, as you can see the memory usage with USE_RESULT doesn't jump, for a reaon. Because data is not stored on the client side. With libmysql you cannot see it, but the usage is there. ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at https://bugs.php.net/bug.php?id=48528 -- Edit this bug report at https://bugs.php.net/bug.php?id=48528&edit=1