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https://issues.apache.org/jira/browse/HDFS-1140?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12885636#action_12885636
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Dmytro Molkov commented on HDFS-1140:
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My patch doesn't have anything to do with all of those -1s.
I reran hudsonQA locally:
[exec] +1 overall.
[exec]
[exec] +1 @author. The patch does not contain any @author tags.
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[exec] +1 tests included. The patch appears to include 3 new or modified
tests.
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[exec] +1 javadoc. The javadoc tool did not generate any warning messages.
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[exec] +1 javac. The applied patch does not increase the total number of
javac compiler warnings.
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[exec] +1 findbugs. The patch does not introduce any new Findbugs warnings.
[exec]
[exec] +1 release audit. The applied patch does not increase the total
number of release audit warnings.
> Speedup INode.getPathComponents
> -------------------------------
>
> Key: HDFS-1140
> URL: https://issues.apache.org/jira/browse/HDFS-1140
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: name-node
> Affects Versions: 0.22.0
> Reporter: Dmytro Molkov
> Assignee: Dmytro Molkov
> Priority: Minor
> Fix For: 0.22.0
>
> Attachments: HDFS-1140.2.patch, HDFS-1140.3.patch, HDFS-1140.4.patch,
> HDFS-1140.patch
>
>
> When the namenode is loading the image there is a significant amount of time
> being spent in the DFSUtil.string2Bytes. We have a very specific workload
> here. The path that namenode does getPathComponents for shares N - 1
> component with the previous path this method was called for (assuming current
> path has N components).
> Hence we can improve the image load time by caching the result of previous
> conversion.
> We thought of using some simple LRU cache for components, but the reality is,
> String.getBytes gets optimized during runtime and LRU cache doesn't perform
> as well, however using just the latest path components and their translation
> to bytes in two arrays gives quite a performance boost.
> I could get another 20% off of the time to load the image on our cluster (30
> seconds vs 24) and I wrote a simple benchmark that tests performance with and
> without caching.
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