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From "Xiao Chen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9314) Improve BlockPlacementPolicyDefault's picking of excess replicas
Date Mon, 23 Nov 2015 22:27:10 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9314?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15023225#comment-15023225

Xiao Chen commented on HDFS-9314:

Thanks [~mingma], good point on {{verifyBlockPlacement}}! 
It's true that  {{BlockPlacementPolicyWithNodeGroup}} does not override {{verifyBlockPlacement}},
but {{BlockPlacementPolicyWithNodeGroup#pickupReplicaSet}} favors node group name when choosing
replicas for delete. I'm not sure replacing it with default is better, or adding {{BlockPlacementPolicyWithNodeGroup#verifyBlockPlacement}}.
Do you think it's safe to remove it? Perhaps that's a separate discussion... Also adding original
author [~djp] for more insights.

> Improve BlockPlacementPolicyDefault's picking of excess replicas
> ----------------------------------------------------------------
>                 Key: HDFS-9314
>                 URL: https://issues.apache.org/jira/browse/HDFS-9314
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Ming Ma
>            Assignee: Xiao Chen
>         Attachments: HDFS-9314.001.patch, HDFS-9314.002.patch, HDFS-9314.003.patch, HDFS-9314.004.patch,
HDFS-9314.005.patch, HDFS-9314.006.patch
> The test case used in HDFS-9313 identified NullPointerException as well as the limitation
of excess replica picking. If the current replicas are on {SSD(rack r1), DISK(rack 2), DISK(rack
3), DISK(rack 3)} and the storage policy changes to HOT_STORAGE_POLICY_ID, BlockPlacementPolicyDefault's
won't be able to delete SSD replica.

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