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@@ -107,6 +107,36 @@ for both files and directories, MUST always return `true` to the `isEncrypted()`
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predicate. This can be done by setting the `encrypted` flag to true when creating
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the `FileStatus` instance.
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+
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+### `msync()`
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+
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+Synchronize metadata state of the client with the latest state of the metadata
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+service of the FileSystem.
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+
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+In highly available FileSystems standby service can be used as a read-only
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+metadata replica. This call is essential to guarantee consistency of
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+reads from the standby replica and to avoid stale reads.
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+
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+It is currently only implemented for HDFS and others will just throw
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+`UnsupportedOperationException`.
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+
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+#### Preconditions
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+
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+
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+#### Postconditions
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+
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+This call internally records the state of the metadata service at the time of
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+the call. This guarantees consistency of subsequent reads from any metadata
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+replica. It assures the client will never access the state of the metadata that
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+preceded the recorded state.
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+
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+#### HDFS implementation notes
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+
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+HDFS supports `msync()` in HA mode by calling the Active NameNode and requesting
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+its latest journal transaction ID. For more details see HDFS documentation
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+[Consistent Reads from HDFS Observer NameNode](https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-hdfs/ObserverNameNode.html)
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+
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+
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### `Path getHomeDirectory()`
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The function `getHomeDirectory` returns the home directory for the FileSystem
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He Xiaoqiao