Bug #71468 [Nab]: increased memory usage with mysqli in php 7

Edit report at https://bugs.php.net/bug.php?id=71468&edit=1 ID: 71468 Updated by: nikic@php.net Reported by: ryan dot brothers at gmail dot com Summary: increased memory usage with mysqli in php 7 Status: Not a bug Type: Bug Package: MySQLi related Operating System: Linux PHP Version: 7.0.2 Block user comment: N Private report: N New Comment: I've implemented some tweaks in master to reduce memory usage for this case (https://github.com/php/php-src/commit/2d1559f827477963a3f8a40af64212a409ba9457). There's more that can be done here, but this was the lowest hanging fruit. Previous Comments: ------------------------------------------------------------------------ [2016-02-22 18:23:25] rendername at gmail dot com Ok, we maked new tests to see, how much memory was used for mysqli_query on process: PHP5: before query 23m, after 237m => so we have 214m (memory_get_usage 45m) NOT OK PHP7: before query 20m, after 270m => so we have 250m (memory_get_usage 250m) OK So, php7 need a little more memory for this query, but we get memory usage correctly. ------------------------------------------------------------------------ [2016-02-22 16:18:41] ryan dot brothers at gmail dot com Thanks for the feedback. I understand the changes, but my scripts in PHP 7 are hitting the memory limit when they didn't in PHP 5.6, yet one of the advantages of PHP 7 is reduced memory usage. Is there someone more familiar with the change in mysqlnd that can look into it further to determine if PHP 7 will use more memory than PHP 5.6 and not less? ------------------------------------------------------------------------ [2016-02-22 15:59:49] nikic@php.net Which isn't to say that there is nothing wrong with how mysqlnd manages memory. I'm not familiar with mysqlnd, but the way this works does look distinctly weird. Apart from wasting memory by being unnecessarily generic (having free_chunk and resize_chunk with always the same values, for every single chunk) it's very odd to see the chunks being allocated at all -- what's the point of using an arena allocator if you still use a full blown memory manager for the metadata? ------------------------------------------------------------------------ [2016-02-22 15:38:16] nikic@php.net store_result uses mysqlnd mempool chunks. In PHP 5.6 those used the system allocator (http://lxr.php.net/xref/PHP_5_6/ext/mysqlnd/mysqlnd_block_alloc.c#120). In PHP 7.0 they use the Zend MM (http://lxr.php.net/xref/PHP_MASTER/ext/mysqlnd/mysqlnd_block_alloc.c#119). So the memory usage didn't actually change (or rather, it did change, but not in a bad way), it simply wasn't reported previously by memory_get_usage(). ------------------------------------------------------------------------ [2016-02-22 14:36:08] ryan dot brothers at gmail dot com Yes, I am using mysqlnd. I confirmed I'm seeing the memory usage increase comparing the latest PHP 5.6.18 and PHP 7.0.3 using the reproduce script above. 5.6.18: mysqlnd 5.0.11-dev - 20120503 - $Id: 76b08b24596e12d4553bd41fc93cccd5bac2fe7a $ 7.0.3: mysqlnd 5.0.12-dev - 20150407 - $Id: f59eb767fe17a6679589b5c076d9fa88d3d4eac0 $ ------------------------------------------------------------------------ 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=71468 -- Edit this bug report at https://bugs.php.net/bug.php?id=71468&edit=1