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From "Stephen Pain" <stephen.p...@db.com>
Subject Re: WebLogic 8.1 and Chainsaw
Date Fri, 17 Sep 2004 09:01:40 GMT

We were using chainsaw to monitor WL 8.1 too, using a SocketHubAppender (so that multiple
chainsaw clients could easily connect to receive the logs) - it's especially useful for us
because we don't have direct access to the drive that hosts the log files (we have to access
them via a web portal). We found that if chainsaw was left connected to the server, collecting
log events over a long period of time but not being looked at (eg over a lunch break) we could
hang all the EJBs that used log4j.

We've now switched to a JMSAppender, writing to a non-persistent topic with a short TTL (a
few seconds, I think).  It's more complicated than a SocketHubAppender and has its own problems
(including that you can no longer run chainsaw using webstart, due to a bug in weblogic preventing
it being used with webstart), but it should be completely safe in a production environment.

As I understand it, an AsyncAppender wouldn't actually prevent this kind of issue - just delay
it... when the AsyncAppender's buffer also fills up, it'll hang in the same way (correct me
if I'm wrong?)

Cheers,
Stephen




                                                                                         
                                                                                       
                      Jeff Longland                                                      
                                                                                       
                      <jlongla2@uwo.ca>        To:       Log4J Users List <log4j-user@logging.apache.org>
                                                                       
                                               cc:                                       
                                                                                       
                      17/09/2004 01:11         Subject:  Re: WebLogic 8.1 and Chainsaw   
                                                                                       
                      Please respond to                                                  
                                                                                       
                      "Log4J Users                                                       
                                                                                       
                      List"                                                              
                                                                                       
                                                                                         
                                                                                       
                                                                                         
                                                                                       




Just took a look at the docs for AsyncAppender - because it runs on its
own thread, should Chainsaw ever hang - the only thing affected is
logging, correct?

I'm in complete agreement Paul - "The penalty, like the normal cost of
any logging, is often worth the price".  It was suggested to me that if
I wanted to monitor a production system with Chainsaw that I should
consider binding traffic to a different network interface.  This would
alleviate some network traffic, but not the overhead of serializing.
Generally speaking, what sort of resources does a socket(hub)appender
consume?

Jeff

Paul Smith wrote:
>>I'm currently administering a Java app running on WebLogic 8.1.  The app
>>uses log4j to handle logging events and I have setup a few socket
>>appenders to monitor classes important in our day-to-day operations.
>>Chainsaw has been great for staying on top of critical errors real-time
>>instead of the traditional tail/grep/less method.  While speaking with a
>>vendor rep, I was informed that running Chainsaw could be detrimental to
>>a production system.  The vendor's belief is that a hang in the Chainsaw
>>client could cause WebLogic to hang.  I was just curious if there's any
>>validity to such a claim?
>
>
> It is potentially possible that a hang in a Chainsaw client could prevent
> the server thread that is doing the appending from continuing, which is why
> you could consider wrapping the SocketAppender or SocketHubAppender in a
> AsyncAppender.  Shutting down Chainsaw or killing it would free that thread
> immediately though.
>
> I've never had any problems monitoring a production box with Chainsaw.
> Under seriously loaded systems the cost of sending the data over the socket
> could add some delays, but then when it's under load, you're probably
> interested in what's going on anyway.... The penalty, like the normal cost
> of any logging, is often worth the price.
>
> This is all IMHO of course.  YMMV.
>
> Paul Smith
>
>
>
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