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# "Apache Hadoop"  2.9.1 Release Notes

These release notes cover new developer and user-facing incompatibilities, important issues, features, and major improvements.


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* [HADOOP-12756](https://issues.apache.org/jira/browse/HADOOP-12756) | *Major* | **Incorporate Aliyun OSS file system implementation**

Aliyun OSS is widely used among China’s cloud users and this work implemented a new Hadoop compatible filesystem AliyunOSSFileSystem with oss scheme, similar to the s3a and azure support.


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* [HADOOP-14964](https://issues.apache.org/jira/browse/HADOOP-14964) | *Major* | **AliyunOSS: backport Aliyun OSS module to branch-2**

Aliyun OSS is widely used among China’s cloud users and this work implemented a new Hadoop compatible filesystem AliyunOSSFileSystem with oss:// scheme, similar to the s3a and azure support.


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* [HDFS-12883](https://issues.apache.org/jira/browse/HDFS-12883) | *Major* | **RBF: Document Router and State Store metrics**

This JIRA makes following change:
Change Router metrics context from 'router' to 'dfs'.


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* [HDFS-12895](https://issues.apache.org/jira/browse/HDFS-12895) | *Major* | **RBF: Add ACL support for mount table**

Mount tables support ACL, The users won't be able to modify their own entries (we are assuming these old (no-permissions before) mount table with owner:superuser, group:supergroup, permission:755 as the default permissions).  The fix way is login as superuser to modify these mount table entries.


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* [YARN-7190](https://issues.apache.org/jira/browse/YARN-7190) | *Major* | **Ensure only NM classpath in 2.x gets TSv2 related hbase jars, not the user classpath**

Ensure only NM classpath in 2.x gets TSv2 related hbase jars, not the user classpath.


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* [HADOOP-15156](https://issues.apache.org/jira/browse/HADOOP-15156) | *Major* | **backport HADOOP-15086 rename fix to branch-2**

[WASB] Fix Azure implementation of Filesystem.rename to ensure that at most one operation succeeds when there are multiple, concurrent rename operations targeting the same destination file.


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* [HADOOP-15027](https://issues.apache.org/jira/browse/HADOOP-15027) | *Major* | **AliyunOSS: Support multi-thread pre-read to improve sequential read from Hadoop to Aliyun OSS performance**

Support multi-thread pre-read in AliyunOSSInputStream to improve the sequential read performance from Hadoop to Aliyun OSS.


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* [HDFS-13083](https://issues.apache.org/jira/browse/HDFS-13083) | *Major* | **RBF: Fix doc error setting up client**

Fix the document error of setting up HFDS Router Federation


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* [HDFS-13099](https://issues.apache.org/jira/browse/HDFS-13099) | *Minor* | **RBF: Use the ZooKeeper as the default State Store**

Change default State Store from local file to ZooKeeper. This will require additional zk address to be configured.