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From "Stephen Pain" <stephen.p...@db.com>
Subject Re: WebLogic 8.1 and Chainsaw
Date Wed, 22 Sep 2004 15:37:25 GMT

> Coming back to the problem at hand, we should investigate why chainsaw
> blocks   after  a  while,   because  if   chainsaw  is   blocked,  all
> AsyncAppender can do is to delay  disaster by only a few seconds or at
> most few minutes.

I haven't found (or tried to find) a guaranteed way to reproduce the problem - however if
I was going to try to make it happen, I would do this:

      1. set up chainsaw (on a windows XP machine) with a SocketHubReceiver listening to a
moderately active appender (say 30-50 events/second)
      2. enable the cyclic buffer, with a large buffer size (~100,000 events)
      3. lock the screen and leave it overnight (or over lunch if you're feeling (un)lucky)

I think, although all the evidence is circumstantial, that locking the screen could be important.
I've never seen chainsaw lock up while it was being used, only when unattended.

If anyone has the time to attempt this test, it would help if there was a second appender
defined, writing to a file or to stdout so that you can monitor it from a different box and
tell when disaster has occurred without having to unlock the screen where chainsaw is running.

As an alternative solution to the JMSAppender (which is quite fiddly and, some would say,
rather heavyweight), maybe a RobustAsyncAppender that drops old events when the buffer is
full would be a good solution?  Or even a property of AsyncAppender that could be set in the
config to give this behaviour?  Even if a problem is found and fixed with chainsaw, the fact
that it's theoretically possible to lock up the system is enough to stop us using the SocketHubAppender
- on the other hand if we could guarantee it would be safe by protecting the appender, I think
the simple socket solution would be preferable to JMSAppender in most cases.

Cheers,
Stephen


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