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From "Xiao Chen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9314) Improve BlockPlacementPolicyDefault's picking of excess replicas
Date Fri, 20 Nov 2015 00:02:11 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9314?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15014801#comment-15014801
] 

Xiao Chen commented on HDFS-9314:
---------------------------------

Thanks [~mingma] for the review, I'll be working on the next rev.
1 quick clarification: I thought about passing in {{rackMap}}, but that needs to add the extra
parameter to both {{chooseReplicaToDelete}} and {{pickupReplicaSet}}.
- I guess {{@VisibleForTesting public chooseReplicaToDelete}} should be fine. 
- But changing the {{protected pickupReplicaSet}} would require modifying all subclasses of
{{BlockPlacementPolicyDefault}}, which is marked as {{@InterfaceAudience.Private}} so [no
external subclasses are expected|https://hadoop.apache.org/docs/r2.7.1/api/org/apache/hadoop/classification/InterfaceAudience.html].
So we'll just update all usages in current code and not worry about compatibility.

Are we on the same page here?

> 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
>
>
> 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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