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From "Ariel Weisberg (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8630) Faster sequential IO (on compaction, streaming, etc)
Date Mon, 17 Aug 2015 23:09:47 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8630?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14700401#comment-14700401
] 

Ariel Weisberg commented on CASSANDRA-8630:
-------------------------------------------

||Version|Time 1|Time 2|Time 3|
|8630 uncompressed|197|204|198|
|8630 compressed|263|262|261|
|3.x uncompressed|199|198|198|
|3.x compressed|200|198|198|

My intuition is that the compressed case has something bad happening, and that there is no
impact from the changes in the uncompressed case. That kind of suggests the time/bottleneck
is elsewhere. I am looking at the flight recordings now.

Did you measure on OS X or Linux? FYI I usually set the file read and write and contention
thresholds to one millisecond. Doesn't seem to impact performance, but does provide a clearer
picture.

> 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,
flight_recorder_002_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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