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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8630) Faster sequencial IO (on compaction, streaming, etc)
Date Thu, 15 Jan 2015 19:04:35 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8630?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14279113#comment-14279113
] 

Benedict commented on CASSANDRA-8630:
-------------------------------------

Ha. I'm kind of amazed we've not spotted this before.

I'm not convinced by the exact tack you've taken, but this should definitely be fixed. The
best fix is probably to explicitly override getLong, getInt, etc, since all of the readers
have a buffer that can be used (if it crosses a buffer boundary, we can simply rebuffer slightly
less than a full buffer), thus keeping garbage to a minimum

> Faster sequencial IO (on compaction, streaming, etc)
> ----------------------------------------------------
>
>                 Key: CASSANDRA-8630
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8630
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Oleg Anastasyev
>         Attachments: 8630-FasterSequencialReadsAndWrites.txt, cpu_load.png
>
>
> 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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