HADOOP-11579. Documentation for truncate. Contributed by Konstantin Shvachko.
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@ -582,6 +582,8 @@ Release 2.7.0 - UNRELEASED
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HADOOP-11520. Clean incomplete multi-part uploads in S3A tests.
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(Thomas Demoor via stevel)
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HADOOP-11579. Documentation for truncate. (shv)
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OPTIMIZATIONS
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HADOOP-11323. WritableComparator#compare keeps reference to byte array.
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@ -54,6 +54,7 @@
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* [test](#test)
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* [text](#text)
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* [touchz](#touchz)
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* [truncate](#truncate)
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* [usage](#usage)
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Overview
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@ -681,6 +682,25 @@ Example:
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Exit Code: Returns 0 on success and -1 on error.
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truncate
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--------
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Usage: `hadoop fs -truncate [-w] <length> <paths>`
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Truncate all files that match the specified file pattern
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to the specified length.
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Options:
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* The -w flag requests that the command waits for block recovery to complete, if necessary.
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Without -w flag the file may remain unclosed for some time while the recovery is in progress.
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During this time file cannot be reopened for append.
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Example:
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* `hadoop fs -truncate 55 /user/hadoop/file1 /user/hadoop/file2`
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* `hadoop fs -truncate -w 127 hdfs://nn1.example.com/user/hadoop/file1`
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usage
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-----
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@ -831,3 +831,38 @@ HDFS's restrictions may be an implementation detail of how it implements
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a sequence. As no other filesystem in the Hadoop core codebase
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implements this method, there is no way to distinguish implementation detail.
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from specification.
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### `boolean truncate(Path p, long newLength)`
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Truncate file `p` to the specified `newLength`.
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Implementations MAY throw `UnsupportedOperationException`.
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#### Preconditions
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if not exists(FS, p) : raise FileNotFoundException
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if isDir(FS, p) : raise [FileNotFoundException, IOException]
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if newLength < 0 || newLength > len(FS.Files[p]) : raise HadoopIllegalArgumentException
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HDFS: The source file MUST be closed.
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Truncate cannot be performed on a file, which is open for writing or appending.
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#### Postconditions
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FS' where:
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len(FS.Files[p]) = newLength
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Return: `true`, if truncation is finished and the file can be immediately
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opened for appending, or `false` otherwise.
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HDFS: HDFS reutrns `false` to indicate that a background process of adjusting
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the length of the last block has been started, and clients should wait for it
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to complete before they can proceed with further file updates.
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#### Concurrency
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If an input stream is open when truncate() occurs, the outcome of read
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operations related to the part of the file being truncated is undefined.
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