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https://issues.apache.org/jira/browse/HDFS-7433?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14224667#comment-14224667
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Daryn Sharp commented on HDFS-7433:
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My bad mentioning {{datanodeMap}} - juggling too many changes. {{DatanodeIDs}}
are added to collections in many other places, and equality checks occur often.
My more general point is mutable hashCodes are a hidden landmine which is why
I filed another jira. Dynamic computation of the xfer addr (and by extension
the hash) is inefficient and generates a lot of garbage.
I'm checking out the odd test failures. They don't appear related, at least
the xml parsing and class def not founds.
> DatanodeMap lookups & DatanodeID hashCodes are inefficient
> ----------------------------------------------------------
>
> Key: HDFS-7433
> URL: https://issues.apache.org/jira/browse/HDFS-7433
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Affects Versions: 2.0.0-alpha, 3.0.0
> Reporter: Daryn Sharp
> Assignee: Daryn Sharp
> Priority: Critical
> Attachments: HDFS-7433.patch
>
>
> The datanode map is currently a {{TreeMap}}. For many thousands of
> datanodes, tree lookups are ~10X more expensive than a {{HashMap}}.
> Insertions and removals are up to 100X more expensive.
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