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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: Monitoring Connections
Date Thu, 08 Oct 2015 17:27:21 GMT
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Aurélien,

On 10/7/15 5:59 PM, Aurélien Terrestris wrote:
> when this happens you can do a thread-dump (kill -3 pid on Linux
> platforms) and you would see if there is a lock on JDBC objects, or
> anything else synchronized (from the Collections like Hashtable).
> Not easy for beginners to understand a dump, but worth learning.

+1

This is the only way to find out what's going on. All other monitoring
solutions will just tell you that *something* is wrong, but this will
give you details.

> Very often an application will slow down because Garbage
> Collection, and the GC thread will be the only one working at that
> time. Please use the verbose settings to have all your Tomcats log
> GC activity. This is useful for both live and after time analysis.

This is pretty unlikely for the reported observations, since Tomcat
slows down and stops responding (presumably until restarted). That is
more likely to be something like database connection pool being
exhausted due to poor resource management rather than out-of-control
GC activity.

> You won't monitor mod_proxy, this has no sense.

I disagree. The connection can go down for various reasons. But I
suspect that's not the problem in this case.

> If you suspect a network flood, do a 'netstat -an' to see how many
> connections are used by your Apache (both ESTABLISHED and
> TIME_WAIT). However, you might need to set timeout and flushpacket
> on your proxypass directive when your application has such
> requirements (see HTTPD doc for this settings). To know if you're 
> flooded, you can do a 'ps -eaf | grep [h]ttp' and you would see
> many httpd process, it is similar to the netstat result more or
> less.

+1

> If you enjoy live monitoring, you need to have a look on
> Christopher's presentation ( 
> http://events.linuxfoundation.org/sites/events/files/slides/Monitoring
%20Apache%20Tomcat%20with%20JMX.pdf
>
> 
) who posts many answers to this mailing list.

Live monitoring is the only way to go, unless you want your customers
to surprise you with performance problems on your own site. :)

- -chris
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