PHP supports a virtually infinite call stack. However, the function call hook provided by the Zend Engine, zend_execute_ex (named zend_execute on PHP 5.4), calls PHP methods and functions using the native C stack. This in turn can cause a stack overflow when the call stack in PHP becomes extra deep.

Starting with ddtrace version 0.48.0, the PHP tracer uses the zend_execute_ex hook on PHP 5. The PHP tracer emits a warning when the call stack reaches 512 frames deep. You can disable this warning by setting the environment variable DD_TRACE_WARN_CALL_STACK_DEPTH=0.

To accommodate PHP applications with deep call stacks, adjust the stack size limit on the host machine. To see the existing stack size, run:

ulimit -s

For example: if the existing stack size is 8192, you may wish to double it by setting a new stack size of 16384.

sudo ulimit -s 16384