Jing Zhao created HDFS-4093:
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Summary: In branch-1-win, AzureBlockPlacementPolicy#chooseTarget
only returns one DN when replication factor is greater than 3.
Key: HDFS-4093
URL: https://issues.apache.org/jira/browse/HDFS-4093
Project: Hadoop HDFS
Issue Type: Bug
Reporter: Jing Zhao
Assignee: Jing Zhao
In branch-1-win, when AzureBlockPlacementPolicy (which extends the
BlockPlacementPolicyDefault) is used, if the client increases the number of
replicas (e.g., from 3 to 10), AzureBlockPlacementPolicy#chooseTarget will
return only 1 Datanode each time. Thus in
FSNameSystem#computeReplicationWorkForBlock, it is possible that the
replication monitor may choose a datanode that has been chosen as target but
still in the pendingReplications (because computeReplicationWorkForBlock does
not check the pending replication before doing the chooseTarget).
To avoid this "hit-the-same-datanode" scenario, we modify the
AzureBlockPlacementPolicy#chooseTarget to make it return multiple DN.
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