huhaiyang

HDFS-16775.Improve BlockPlacementPolicyRackFaultTolerant's chooseOnce

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### Description of PR HDFS-16775. ### For code changes: Improve BlockPlacementPolicyRackFaultTolerant's chooseOnce

HDFS-17352. Add configuration to control whether DN delete this replica from disk when client requests a missing block

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### Description of PR https://issues.apache.org/jira/browse/HDFS-17352 As discussed at https://github.com/apache/hadoop/pull/6464#issuecomment-1902959898 we should add configuration to control whether DN delete this replica from disk when client requests a missing block.

HDFS-17564. Erasure Coding: Fix the issue of inaccurate metrics when decommission mark busy DN

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### Description of PR https://issues.apache.org/jira/browse/HDFS-17564 If DataNode is marked as busy and contains many EC blocks, when running decommission DataNode, when execute ErasureCodingWork#addTaskToDatanode, here will no replication work will be...

HDFS-17559. Fix the uuid as null in NameNodeMXBean

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### Description of PR https://issues.apache.org/jira/browse/HDFS-17559 If there is datanode info in includes, but the datanode service is not currently started, the uuid of the datanode will be null. when get...

HDFS-17557. Fix bug for TestRedundancyMonitor#testChooseTargetWhenAllDataNodesStop

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### Description of PR https://issues.apache.org/jira/browse/HDFS-17557 Due to the modification in [HDFS-16456](https://issues.apache.org/jira/browse/HDFS-16456), the current UT has not been able to run successfully, so we need to fix it.

HDFS-16757. Add a new method copyBlockCrossNamespace to DataNode

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### Description of PR As described in https://issues.apache.org/jira/browse/HDFS-16757 ： Add a new method copyBlockCrossNamespace to Datanode to support fast copy.