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https://issues.apache.org/jira/browse/HDFS-1140?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12886103#action_12886103
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Tsz Wo (Nicholas), SZE commented on HDFS-1140:
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> I believe this because org.apache.hadoop.hdfs.util.GSet links java.util.Map
> and Set in its javaDocs. ...
Konstantin, are you sure? The GSet patch was committed in May and there is no
javadoc warning for quite a few Hudson builds, e.g.
[this|https://issues.apache.org/jira/browse/HDFS-1258?focusedCommentId=12883441&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12883441],
[this|https://issues.apache.org/jira/browse/HDFS-1093?focusedCommentId=12884884&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12884884]
and
[this|https://issues.apache.org/jira/browse/HDFS-1093?focusedCommentId=12884883&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12884883].
> 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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