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https://issues.apache.org/jira/browse/HDFS-8647?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14964327#comment-14964327
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Ming Ma commented on HDFS-8647:
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Thanks [~brahmareddy]! It looks great. Sorry, there is one question I didn't
mentioned last time.
It seems the replica-to-be-deleted will be removed from the candidates in
{{BlockPlacementPolicyDefault#chooseReplicasToDelete}}:
{{candidates.remove(cur);}}. It will be removed again later in
{{BlockManager#processChosenExcessReplica}}: {{nonExcess.remove(chosen);}}.
Even though this doesn't cause any issue; it is better to keep the semantics of
{{BlockPlacementPolicyDefault#chooseReplicasToDelete}} to not modify the
candidates. What do you think? If you agree, after you update the patch and the
patch passes jenkins, it is good to go.
In addition, I have used the local repo to evaluate how hard it is to
cherry-pick to branch-2. It turns out I had to spend some time manually
resolving the issues. I have taken care of that and you don't need to provide a
version for branch-2. The patch passed HDFS unit tests in branch-2.
> Abstract BlockManager's rack policy into BlockPlacementPolicy
> -------------------------------------------------------------
>
> Key: HDFS-8647
> URL: https://issues.apache.org/jira/browse/HDFS-8647
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Ming Ma
> Assignee: Brahma Reddy Battula
> Attachments: HDFS-8647-001.patch, HDFS-8647-002.patch,
> HDFS-8647-003.patch, HDFS-8647-004.patch, HDFS-8647-004.patch,
> HDFS-8647-005.patch, HDFS-8647-006.patch, HDFS-8647-007.patch
>
>
> Sometimes we want to have namenode use alternative block placement policy
> such as upgrade domains in HDFS-7541.
> BlockManager has built-in assumption about rack policy in functions such as
> useDelHint, blockHasEnoughRacks. That means when we have new block placement
> policy, we need to modify BlockManager to account for the new policy. Ideally
> BlockManager should ask BlockPlacementPolicy object instead. That will allow
> us to provide new BlockPlacementPolicy without changing BlockManager.
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