This morning, I was presented with quite the conundrum: one of my servers suddently started having about 4x the normal MySQL traffic it would have in a morning, and I had no indication as to why this was happening; traffic to the sites on the server was steady (no spikes), and I couldn't find any problems with any of the sites.
However, after inspecting the Apache (httpd) error logs for the Drupal 6 sites, I found a ton of PHP warnings on almost all the sites. Something like the following:
[Tue Nov 08 11:25:51 2011] [error] [client IP] PHP Warning: date_default_timezone_get(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/Chicago' for 'CST/-6.0/no DST' instead in /path/to/drupal6/sites/opensourcecatholic.com/settings.php on line 149<br />
As it turns out, the fix for date.timezone problems with PHP 5.3.x and Drupal 6.x mentioned in http://drupal.org/node/325827 (namely, adding
ini_set('date.timezone', date_default_timezone_get()); to the other ini_set() functions in settings.php) doesn't work that well for daylight savings time.
So, I've changed all those ini_set() functions in my Drupal 6 sites' settings.php files to explicitly set the default server timezone (in my case,
ini_set('date.timezone','America/Chicago');), and now the error logs and watchdog errors written to the database are much more compact :)
I always leave watchdog database logging on for one or two of the sites on a server for precisely this reason: if something goes haywire, I can quickly notice something's awry in my server's munin stats. Then I hop over to the apache error logs and see exactly what's up.