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https://issues.apache.org/jira/browse/HDFS-7435?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15032285#comment-15032285
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Mingliang Liu commented on HDFS-7435:
-------------------------------------
Thanks for your comment, [~daryn] and [~shv]. I started to work on
{{NNThroughputBenchmark}} just recently and knew nothing about it before that.
If the empty block report list in this patch was not intensional, I think I
don't need more context of this patch. Sure I'd like to make the change as we
discussed above. The jira is [HDFS-9484]. Let's continue further discussion on
the fix there.
The reason why the unit tests could pass may be that the
{{TestNNThroughputBenchmark}} is rather a driver to run the benchmark with
default parameters than a real unit test that asserts expected behavior for
different scenarios. If we need a sophisticated unit test, perhaps we can
address it separately.
> PB encoding of block reports is very inefficient
> ------------------------------------------------
>
> Key: HDFS-7435
> URL: https://issues.apache.org/jira/browse/HDFS-7435
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode, namenode
> Affects Versions: 2.0.0-alpha, 3.0.0
> Reporter: Daryn Sharp
> Assignee: Daryn Sharp
> Priority: Critical
> Fix For: 2.7.0
>
> Attachments: HDFS-7435.000.patch, HDFS-7435.001.patch,
> HDFS-7435.002.patch, HDFS-7435.patch, HDFS-7435.patch, HDFS-7435.patch,
> HDFS-7435.patch, HDFS-7435.patch, HDFS-7435.patch, HDFS-7435.patch,
> HDFS-7435.patch, HDFS-7435.patch
>
>
> Block reports are encoded as a PB repeating long. Repeating fields use an
> {{ArrayList}} with default capacity of 10. A block report containing tens or
> hundreds of thousand of longs (3 for each replica) is extremely expensive
> since the {{ArrayList}} must realloc many times. Also, decoding repeating
> fields will box the primitive longs which must then be unboxed.
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