I had an interesting IRC discussion the other day with Monty Taylor about what turned out to be a limitation in Valgrind with respect to debugging memory leaks in dynamically loaded plugins.

Monty Taylor's original problem was with Drizzle, but as it turns out, it is common to all of the MySQL-derived code bases. When there is a memory leak from an allocation in a dynamically loaded plugin, Valgrind will detect the leak, but the part of the stack trace that is within the plugin shows up as an unhelpful three question marks "???":

==1287== 400 bytes in 4 blocks are definitely lost in loss record 5 of 8
==1287==    at 0x4C22FAB: malloc (vg_replace_malloc.c:207)
==1287==    by 0x126A2186: ???
==1287==    by 0x7C8E01: ha_initialize_handlerton(st_plugin_int*) (handler.cc:429)
==1287==    by 0x88ADD6:

Most of this stuff is not PHP specific, and Python or Ruby or Java or .NET developers can use the tools in this talk.

The session on joind.in, with user comments/feedback, is at http://joind.in/talk/view/1320.

Slides are at http://talks.php.net/show/confoo10

“My name is Rasmus, I’ve been around for a long time. I’ve been doing this web stuff since 1992/1993.”

“Generally performance is not a PHP problem.” Webservers not config’d, no expire headers on images, no favicon.

Tools: Firefox/Firebug extension called YSlow (developed by yahoo) gives you a grade on your site.

Like so many others, I got interested in the Drizzle project when it started. Some good ideas, lots of enthusiasm, and just pure GPL license, no "yes, we will take your work for free and sell proprietary licenses to it" SCA.

I even started contributing some development, fixing a number of Valgrind-detected bugs in Drizzle. I am proud that we kept the MySQL code 100% free of Valgrind errors, and wanted to help keep the same in Drizzle. So I debugged and fixed quite a few of the Valgrind-detected bugs that had crept in since forking from MySQL.

As I remember, I got down to two or three remaining or so. However, I it did discourage me somewhat to see how quickly these bugs had been allowed to enter the code. I remember one case where there was a Drizzle patch that had tried to simplify some field types. As I remember, the patch tried to simplify the code by eliminating some of