A nice tip for logging data against apache logs within requests. Apache_note is a wrapper for Apache’s table_get and table_set. It edits the table of notes that exists during a request. The table’s purpose is to allow Apache modules to communicate.

if (function_exists('apache_note')) {

    if (isset($_SESSION) && !empty($_SESSION)) {
        apache_note('session_id',     session_id());
        apache_note('users_id',       isset($_SESSION['users_id'])? $_SESSION['users_id'] : null);

    }

    apache_note('start_time',     isset($_SERVER['REQUEST_TIME'])? $_SERVER['REQUEST_TIME'] : null);
    apache_note('end_time',       time());
    apache_note('peak_memory',    memory_get_peak_usage());

}

This will allow the variable to be exposed to apache logs in the form of the following.

LogFormat "%{session_id}n %{users_id}n " combined

You can easily add this globally by using the auto_append_file directive in the php ini.

auto_append_file = /var/www/footer.php

Additionally it is quite handy to include the following in a custom log format for debugging purposes. For example if you have hung apache processes.

Common Log Format with Virtual Host and above params

LogFormat "%v %h %l %u %t \"%r\" %>s %b %B %P %X %{session_id}n %{users_id}n %{peak_memory}n" custom_log

You can take this one step further and log these in realtime using Graphite, Logtailer and logster. This holds the offset from the last time you scanned your logs. So this will give you accurate graphs. I have also added a custom parser for PHP, which can be found here.

An example of this, although does not have any errors shown below (hidden the server names).