Re-introduce FastByteArrayInputStream (and Output equivalent)
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                 Key: CASSANDRA-2820
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2820
             Project: Cassandra
          Issue Type: Improvement
          Components: Core
    Affects Versions: 0.8.0, 0.7.6
         Environment: n/a
            Reporter: Paul Loy
            Priority: Minor


In https://issues.apache.org/jira/browse/CASSANDRA-37 FastByteArrayInputStream 
and FastByteArrayOutputStream were removed due to being code copied from the 
JDK and then subsequently modified. The JDK license is incompatible with Apache 
2 license so the code had to go.

I have since had a look at the performance of the JDK ByteArrayInputStream and 
a FastByteArrayInputStream (i.e. one with synchronized methods made 
un-synchronized) and seen the difference is significant.

After a warmup-period of >10000 loops I get the following for 10000 loops 
through a 128000 byte array:

bais : 3513ms
fbais: 72ms

This varies depending on the OS, machine and Java version, but it's always in 
favour of the FastByteArrayInputStream as you might expect.

Then, at Jonathan Ellis' suggestion, I tried this using a modified Apache 
Harmony ByteArrayInputStream - i.e. one whose license is compatible - and the 
results were the same. A significant boost.

I will attach a patch with changes for the 0.8.0 tag.

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