I must appraise the memory consumption for just one active Apache connection(=Thread) under Ubuntu.
It is possible to monitoring tool which is able to do this? Otherwise, does anybody knows just how much memory an Apache connection roughly needs?
I'm wishing for a lot of solutions :)
Active mod_status module, you will get a study on /server-status page, there's a far more parseable version on /server-status?q=auto. Should you enable ExtendedStatus On you'll have a large amount of info on processes and threads.
This is actually the page utilized by monitoring tools to trace lots of stats parameters, which means you will definitely discover the one you'll need (edit: if it's not memory...) . Be cautious with security/access configurations of the file, it is a nice tool to check on the way your server react to DOS :-)
About memory you have to observe that Apache loves memory, just how much memory per process is dependent on several things (quantity of modules loaded - check that you'll require all of the ones you've, quantity of virtualHosts, etc). But on the stable configuration it doesn't move a great deal (except if you are using PHP scripts rich in memory limit usage...). If you discover memory leaks attempt to limit the amount of demands per process MaxRequests (apache will kill him and set a replacement).
edit: actually very little memory info within the server-status. About monitoring tools, any tool using SNMP MIB-II can track memory usage per process, with average/top/low values for that different children's (Cacti, Nagios, Munin, etc) should you have had a snmpd daemon. Take a look excellent Munin example. It isn't a monitoring of every apache child but you'll have a concept of what you could track with one of these tools. If you don't require a complete monitoring system for example Nagios or Centreon, with alerts, user managmenent, large systems (and when you don't have lots of days for books reading through) Munin is, IMHO, quite a tool to obtain monitoring reviews quite fast.
I am unsure if you will find any tools for carrying this out. However, you could estimate it yourself. Start apache and appearance just how much memory it uses with no periods. Than produce a large quantity of periods and appearance again just how much memory it uses.
You could utilize http://jakarta.apache.org/jmeter/ to produce different workloads.