[
https://issues.apache.org/jira/browse/HADOOP-10681?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14048098#comment-14048098
]
Gopal V commented on HADOOP-10681:
----------------------------------
Since this bug has caused some alarm among those who looked at it, I will
pessimize this a little.
The core open loop which needs per-stream sync is (the correct code version)
{code}
synchronized(compressor) {
compressor.setInput();
while (!compressor.finished()) {
compressor.compress(buffer, 0, buffer.length);
}
}
{code}
I will make sure only this incorrect loop follows the required fast-path.
> Remove synchronized blocks from SnappyCodec and ZlibCodec buffering
> -------------------------------------------------------------------
>
> Key: HADOOP-10681
> URL: https://issues.apache.org/jira/browse/HADOOP-10681
> Project: Hadoop Common
> Issue Type: Bug
> Components: performance
> Affects Versions: 2.2.0, 2.4.0, 2.5.0
> Reporter: Gopal V
> Assignee: Gopal V
> Labels: perfomance
> Attachments: HADOOP-10681.1.patch, compress-cmpxchg-small.png,
> perf-top-spill-merge.png, snappy-perf-unsync.png
>
>
> The current implementation of SnappyCompressor spends more time within the
> java loop of copying from the user buffer into the direct buffer allocated to
> the compressor impl, than the time it takes to compress the buffers.
> !perf-top-spill-merge.png!
> The bottleneck was found to be java monitor code inside SnappyCompressor.
> The methods are neatly inlined by the JIT into the parent caller
> (BlockCompressorStream::write), which unfortunately does not flatten out the
> synchronized blocks.
> !compress-cmpxchg-small.png!
> The loop does a write of small byte[] buffers (each IFile key+value).
> I counted approximately 6 monitor enter/exit blocks per k-v pair written.
--
This message was sent by Atlassian JIRA
(v6.2#6252)
