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https://issues.apache.org/jira/browse/HDFS-9314?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15007524#comment-15007524
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Zhe Zhang commented on HDFS-9314:
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The patch LGTM overall. Only ask is to add a short Javadoc for the new
{{chooseReplicaToDelete}} method.
I think the change fixes the issue for the default BPP. We should probably
address it for {{BlockPlacementPolicyWithNodeGroup}} and
{{BlockPlacementPolicyWithUpgradeDomain}} as follow-on tasks. In both
subclasses {{pickupReplicaSet}} still returns one from two sets, and it's
possible that the picked set doesn't have the appropriate type to delete.
> 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
>
>
> 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 1), DISK(rack 2), DISK(rack 2)} and the storage
> policy changes to HOT_STORAGE_POLICY_ID, BlockPlacementPolicyDefault's won't
> be able to delete SSD replica.
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