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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-9797) Don't wrap byte arrays in SequentialWriter
Date Fri, 17 Jul 2015 08:39:04 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-9797?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Sylvain Lebresne updated CASSANDRA-9797:
----------------------------------------
    Fix Version/s: 2.2.x

> 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
>              Labels: performance
>             Fix For: 3.x, 2.2.x
>
>         Attachments: 9797.txt
>
>
> 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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