I manage a Ubuntu 10.04 server with a couple of domains hosted on it. As I continue to learn more about all these wonderful new (for me), one issue that I have begun to notice is the delay it sometimes takes for the server to respond to certain requests.

As an example, when I view the timeline of events using firebug I can see that most of the time when I make a POST, the server responds in under 100ms. Sometimes, however, there is a substantial delay before the RESPONSE from the server. I can't seem to tell when the delay will happen and when it won't, however, when it happens the delay is always for about 4.5 seconds. The delay seems to happen about 30-40% of the time.

Here is the section of apache2.conf dealing with logs:

#
# The following directives define some format nicknames for use with
# a CustomLog directive (see below).
# If you are behind a reverse proxy, you might want to change %h into %{X-Forwarded-For}i
#
LogFormat "%v:%p %h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" vhost_combined
LogFormat "%h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" combined
LogFormat "%h %l %u %t \"%r\" %>s %O" common
LogFormat "%{Referer}i -> %U" referer
LogFormat "%{User-agent}i" agent

I have no idea where to look to try and debug this problem or investigate further.

Any suggestions?