[RndTbl] Accurate Monitoring of system load

[John Lange]

On Fri, 2005-12-16 at 12:02 -0600, Tim Lavoie wrote:

> 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.

There is a tool called apache-top which tails the log files and gives
you something similar to top. However, this is far from the ideal
solution when you have a web server with 100 sites on it, each with its
own log file.

It also doesn't tell you anything if the load is in a mySQL query. The
web server process can be idle but waiting for a mySQL query.

> 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.

BTW, A great load testing tool is:

http://jakarta.apache.org/jmeter/

But load testing isn't what I need. I don't care how much load the
applications cause when stressed, what I need to know is which
applications are are using the most resources in real-life.

By way of a better example let me give more detail.

Lets say you have a server with 100 clients on it. Some of them busy,
some of them not.

One site may have a very load intensive application on it but that only
gets 1 hit every 10 minutes.

Another site could be getting 1 hit per second but the application is
very light.

The only thing you can tell is that the server is under load. There is
next to no way to determine who is responsible. Just because a site is
getting more traffic doesn't make it load intensive and vs. versa.

What you need is a tool like top but that keeps history and then shows
average load over some given time span.

Regards,
-- 
John Lange
OpenIT ltd. www.Open-IT.ca (204) 885 0872
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