Github user eolivelli commented on the issue:
https://github.com/apache/zookeeper/pull/669
@maoling there is no generic benchmarks.
For instance in Bookkeeper we switched to Netty 4 and now we are able to
leverage all the cool stuff about memory and so we are able to be more
efficient.
Overall by default Netty4 will prefer using off heap memory, this is about
being able to do as few as possible memory copies while passing data to the SO.
The simple switch may or may not make overall performance better or even
worse. There will be knobs to tune.
Netty 3 is almost obsolete and IMHO it is better to stay on the latest and
greatest. Netty4 project is very active.
Another topic will be about refcounting, Netty4 enables even Java programs
to work easy with direct memory and with heap memory and provides very
efficient ways to pool memory and java objects (see the Recycler facility).
So I think this is only the beginning of this journey
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