Sylvain Lebresne created CASSANDRA-9797:
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Summary: Don't wrap byte arrays in SequentialWriter
Key: CASSANDRA-9797
URL: https://issues.apache.org/jira/browse/CASSANDRA-9797
Project: Cassandra
Issue Type: Improvement
Reporter: Sylvain Lebresne
Assignee: Sylvain Lebresne
Priority: Minor
Fix For: 3.x
While profiling a simple stress write run ({{cassandra-stress write n=2000000
-rate threads=50}} to be precise) with Mission Control, I noticed that a non
trivial amount of heap pressure was due to the {{ByteBuffer.wrap()}} call in
{{SequentialWriter.write(byte[])}}. Basically, when writing a byte array, we
wrap it in a ByteBuffer to reuse the {{SequentialWriter.write(ByteBuffer)}}
method. One could have hoped this wrapping would be stack allocated, but if
Mission Control isn't lying (and I was told it's fairly honest on that front),
it's not. And we do use that {{write(byte[])}} method quite a bit, especially
with the new vint encodings since they use a {{byte[]}} thread local buffer and
call that method.
Anyway, it sounds very simple to me to have a more direct {{write(byte[])}}
method, so attaching a patch to do that. A very quick local benchmark seems to
show a little bit less allocation and a slight edge for the branch with this
patch (on top of CASSANDRA-9705 I must add), but that local bench was far from
scientific so happy if someone that knows how to use our perf service want to
give that patch a shot.
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