[logback-user] MDC performance concerns

[Matthew Finn]

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