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https://issues.apache.org/jira/browse/CASSANDRA-8630?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14653738#comment-14653738
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Benedict commented on CASSANDRA-8630:
-------------------------------------
My expectation was that we would extract the existing "is sufficient
remaining?" check, and use this to drive a decision. It doesn't really matter
what we do inside this block, because that is executed infrequently. I would
have a {{long readBytesSlowly(int count)}} method, which we downcast the result
to whatever we have actually read. That method would call {{readNext()}} as
necessary, and would be prevented from being inlined. But that's just how I
would do it, since I prefer not to incur complexity when we know the cost will
be amortized away, nor inline that method and inflate our code size for the
same reason.
I don't think it matters _terribly_, though, and if you or [~stefania] have a
strong opinion I won't stand in the way (unless it happens to trigger a strong
and unexpected anti-opinion)
> Faster sequential IO (on compaction, streaming, etc)
> ----------------------------------------------------
>
> Key: CASSANDRA-8630
> URL: https://issues.apache.org/jira/browse/CASSANDRA-8630
> Project: Cassandra
> Issue Type: Improvement
> Components: Core, Tools
> Reporter: Oleg Anastasyev
> Assignee: Stefania
> Labels: compaction, performance
> Fix For: 3.x
>
> Attachments: 8630-FasterSequencialReadsAndWrites.txt, cpu_load.png,
> flight_recorder_001_files.tar.gz
>
>
> When node is doing a lot of sequencial IO (streaming, compacting, etc) a lot
> of CPU is lost in calls to RAF's int read() and DataOutputStream's write(int).
> This is because default implementations of readShort,readLong, etc as well as
> their matching write* are implemented with numerous calls of byte by byte
> read and write.
> This makes a lot of syscalls as well.
> A quick microbench shows than just reimplementation of these methods in
> either way gives 8x speed increase.
> A patch attached implements RandomAccessReader.read<Type> and
> SequencialWriter.write<Type> methods in more efficient way.
> I also eliminated some extra byte copies in CompositeType.split and
> ColumnNameHelper.maxComponents, which were on my profiler's hotspot method
> list during tests.
> A stress tests on my laptop show that this patch makes compaction 25-30%
> faster on uncompressed sstables and 15% faster for compressed ones.
> A deployment to production shows much less CPU load for compaction.
> (I attached a cpu load graph from one of our production, orange is niced CPU
> load - i.e. compaction; yellow is user - i.e. not compaction related tasks)
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