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From "Virajith Jalaparti (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-12809) [READ] Fix the randomized selection of locations in {{ProvidedBlocksBuilder}}.
Date Wed, 22 Nov 2017 01:42:01 GMT

    [ https://issues.apache.org/jira/browse/HDFS-12809?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16261836#comment-16261836

Virajith Jalaparti commented on HDFS-12809:

[~elgoiri], wrt your [comment|https://issues.apache.org/jira/browse/HDFS-12778?focusedCommentId=16255428&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-16255428]
on HDFS-12778, I filed HDFS-12848. This JIRA is to just fix the random selection policy that
is currently implemented. We can make it pluggable later on.

> [READ] Fix the randomized selection of locations in {{ProvidedBlocksBuilder}}.
> ------------------------------------------------------------------------------
>                 Key: HDFS-12809
>                 URL: https://issues.apache.org/jira/browse/HDFS-12809
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Virajith Jalaparti
>            Assignee: Virajith Jalaparti
>         Attachments: HDFS-12809-HDFS-9806.001.patch
> Calling {{getBlockLocations}} on files that have a PROVIDED replica, results in the datanode
locations being selected at random. Currently, this randomization uses the datanode uuids
to pick a node at random ({{ProvidedDescriptor#choose}}, {{ProvidedDescriptor#chooseRandom}}).
Depending on the distribution of the datanode UUIDs, this can lead to large number of iterations
(which may not terminate) before a location is chosen. This JIRA aims to replace this with
a more efficient randomization strategy.

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