Apache::DebugInfo gives the programmer the ability to monitor various
bits of per-request data.

You can enable Apache::DebugInfo as a PerlInitHandler, in which case it
chooses what request phase to display the appropriate data.  The output
of data can be controlled by setting various variables to On:

  DebugInfo          - enable Apache::DebugInfo handler
  DebugPID           - dumps apache child pid during request init
  DebugHeadersIn     - dumps request headers_in during request init
  DebugDirConfig     - dumps PerlSetVar and PerlAddVar during request init
  DebugGetHandlers   - dumps enabled request handlers during init
  DebugHeadersOut    - dumps request headers_out during request cleanup
  DebugNotes         - dumps request notes during request cleanup
  DebugPNotes        - dumps request pnotes during request cleanup
  DebugTimestamp     - prints localtime at the start of each request
  DebugMarkPhases    - prints the name of the request phase when the
                       phase is entered, prior to any other handlers

WWW: http://search.cpan.org/dist/Apache-DebugInfo/