[RndTbl] Accurate Monitoring of system load

Tim Lavoie tim at fractaldragon.net
Fri Dec 16 12:02:28 CST 2005

>>>>> "John" == John Lange <john.lange at open-it.ca> writes:

    John> Does anyone have any suggestions for accurate monitoring of
    John> system load on web servers?

    John> In the situation where you have a server which is hosting
    John> multiple applications I've found it next to impossible to
    John> determine with any accuracy what applications or pages
    John> within those applications are causing load.

    John> At any given moment its easy to see what is using CPU and
    John> memory. But in the case of a web server these are brief
    John> spikes that don't mean anything. Whats needed is a way to
    John> see what has caused the most load over a given time period
    John> (say the last 10 minutes).

    John> Does anyone have any suggestions for tools that can help
    John> determine load.

Hey John,

There are a couple of things which you can do to figure out what is
going on. I tend to use a couple of additional Apache log directives
to get more info for each request. Adding "%O %I %D" gets you bytes
out, in (say, for big posts) and the request duration in
microseconds. This gives you enough to run an analysis script, or just
use the Mark I Eyeball when things have been acting up. It might also
be useful to log the query string as well, but be careful if you have
apps which pass things like passwords in query parameters; you don't
want those floating around in your logs.

If possible, benchmarking your app or overall site is a helpful exercise,
especially if the tool used allows you to simulate multiple user
sessions. LoadRunner is a commercial (and pricy) tool to do this, but
OpenSTA looks like a reasonable, free alternative. Running a bunch of
concurrent users will help find areas which work OK in development,
but which don't scale well.


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