Ceki,
MDC can't be called per request in my app because each individual
packet during a connection could potentially be handled by a different
thread in a thread pool. This type of scenario is common with any type
of asynchronous network library, where the general goal is to decouple
connections from threads.
Any of the libraries out there based on java.nio would be affected in
the same way:
Apache MINA: http://mina.apache.org/
Coconut AIO: http://coconut.codehaus.org/
IBM AIO: http://www.alphaworks.ibm.com/tech/aio4j
I suppose I can go the route of creating my own MDC implementation,
but I do think that the way MDC was handled in log4j originally (which
appears to have been authored by you :) is more correct, cloning the
HashMap in LoggingEvent and InheritableThreadLocal.childValue.
I have posted bug #150 with a patch :)
http://bugzilla.qos.ch/show_bug.cgi?id=150
Thanks
Matt
On Apr 25, 2008, at 4:20 PM, Ceki Gulcu wrote:
Hello Matthew,
Yikes! The MDC implementation in logback is not intended to be called
in hot spots. You call it when a request arrives. If requests arrive
hundreds of times each milisecond, then there might be a performance
concerns as you point out.
The cloning is done for sake of serialization. I think cloning is
necessary for correct serialization of MDC values. As you point out,
cloning could be done within LoggingEvent.
If you deem that logback's implementation of MDC is too slow for your
purposes (I'd check if that is really true), you could write your own
implementation of MDC and have it interpreted by your own
MDCConverter. In logback, it is rather easy to register your own
pattern converters. Holler if you decide to go down this road and you
need help.
If the above does not work for you, then please kindly enter a bug
report.
There is a reasonably good chance that your proposal will be
implemented.
Matthew Finn wrote:
Hello,
I am interested in converting my application to logback, but I have
some performance concerns about its MDC implementation.
My application uses MDC extensively for async IO, so it may call
MDC.put and MDC.remove extremely frequently, because each thread
may be handling 1000s of interleaved connections using state
machines.
I see in the source for LogbackMDCAdapter that for every call to
MDC.put and MDC.remove, the HashMap is cloned. Could this clone
potentially be handled during the creation of LoggingEvents instead
of the call to MDC? The creation of logging events is expected to
entail memory allocation, so it seems that it would be a better fit
there, even if some applications might have a very low number of
calls to MDC versus logging calls. It seems that the same energy
expended in minimizing log statement impact when logging is turned
off should also apply to MDC calls.
Thanks
Matt
--
Ceki Gülcü
QOS.ch is looking to hire talented developers in Switzerland. If
interested, please contact c e k i AT q o s . c h
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