CASSANDRA-2820 I reintoduced the FastByteArrayInputStream and FastByteArrayOutputStream to cassandra. These steams are un-synchronized versions of the Apache Harmony ByteArrayInputStream and ByteArrayOutputStream respectively.
During my own testing of the streams I found a big difference in the performance of the standard JDK BA*S steams and the FBA*S streams on most JREs. Then cassandra load testing also showed an up to 10% improvement in cassandra performance using these streams.
Then Thrift has TByteArrayOutputStream which contains a way to get the underlying byte buffer without a deep copy that would probably be a good further enhancement.
Patch to follow.