Kihwal Lee created HDFS-12272:
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Summary: chooseRemoteRack() semantics broken in trunk
Key: HDFS-12272
URL: https://issues.apache.org/jira/browse/HDFS-12272
Project: Hadoop HDFS
Issue Type: Bug
Components: block placement
Affects Versions: 3.0.0-alpha3
Reporter: Kihwal Lee
Priority: Critical
The {{chooseRemoteRack()}} method in the default block placement policy was
designed to pick from maximum number of racks. E.g. If asked to pick 2 and
there are 2 or more racks available, the two will be on different racks. It
wasn't implicit or accidental semantics. There was a specific logic in
{{chooseRandom()}} that makes it happen.
This behavior is broken after HDFS-11530 as this logic was removed from
{{chooseRandom()}}. Now the result is unpredictable. Sometimes the replicas end
up in the same rack.
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