Derick Rethans has a new post with his own suggestion about using the right debugging tools to help track down a problem (based on some of his own experience debugging the MongoDB PHP extension).

A while ago, we updated the MongoDB PHP driver's embedded C library to a new version. The C library handles most of the connection management and other low level tasks that the PHP driver needs to successfully talk to MongoDB deployments, especially in replicated environments where servers might disappear for maintenance or hardware failures.

After upgrading a related library, he ended up with a failing test related to Atlas connectivity. He walks through the process he took to try and debug the issue using GDB to see where the execution was failing using various techniques. This included looking through the backtrace and, not noticing anything out of the ordinary, going for a walk. Upon returning he noticed an odd line in the backtrace that, after some additional tracking using a GDB helper, showed the problem to be with how the query options are defined and not reset in a loop.

Derick Rethans has a new post to his blog showing how you can, using a few simple unix tools, figure out what PHP is doing when your scripts are executing.

Sometimes when you have a long running PHP script, you might wonder what the hell it is doing at the moment. There are a few tools that can help you to find out, without having to stop the script. Some of these work only on Linux.

He shows you how to use the following commands to track down exactly what your process is working on: strace, ltrace and gdb (a handy debugger that will probably give you more information than you're looking for). He includes some sample output for the commands and gives an example of a PHP script-to-gdb output relationship.

Derick Rethans has shared a quick tip for locating a code crashing kind of problem with your application when something like XDebug isn't around.

However, because we as PHP developers are lazy, provide a few GDB tricks to make this easier. First of all, it's only really going to work if you haven't stripped the symbols from your PHP and Apache binaries. Secondly, you still need to have the PHP source lying around somewhere.

He suggests using GDB to run the backtraces and create a file to help you track down the infinite recursion problem that could be giving you issues.