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https://issues.apache.org/jira/browse/HDFS-1140?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12867190#action_12867190
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Hairong Kuang commented on HDFS-1140:
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> two different abstractions that are communicating via String paths
No I do not think so. What matters is the encoding. The goal is to convert
what's on disk to java UTF8 encoding as stored in memory. Currently it happens
that what's on disk uses the same encoding as what's in the memory. Why bother
converting to String first.
> Speedup INode.getPathComponents
> -------------------------------
>
> Key: HDFS-1140
> URL: https://issues.apache.org/jira/browse/HDFS-1140
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: Dmytro Molkov
> Assignee: Dmytro Molkov
> Attachments: 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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