AbstractMemoryHttpData performance issue when using composite buffer

[pderop]

Buffers appended to the AbstractMemoryHttpData are appended to a CompositeBuffer using "extendWith" method.
But it seems there is a performance issue with extendsWith method. Maybe the CompositeBuffer API is not used appropriately or maybe there is room for optimisation in the CompositeBuffer implementation, I don't know for the moment.

I'm attaching a benchmark which is reproducing the performance issue:
buffer.composite.benchmark.tgz

here are the results, where we can observe the performance issue:

Benchmark Mode Cnt Score Error Units
MyBenchmark.compositeBufferBenchmark thrpt 14116.317 ops/s
MyBenchmark.compositeByteBufBenchmark thrpt 153964.596 ops/s

[pderop]

we should check if the recent netty issue is fixing the performance issue when using composite extendWith method (see netty PR #12759).