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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HDFS-946) NameNode should not return full path name when lisitng a diretory or getting the status of a file
Date Thu, 11 Feb 2010 00:02:29 GMT

     [ https://issues.apache.org/jira/browse/HDFS-946?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Hairong Kuang updated HDFS-946:

    Attachment: HDFSFileStatus.patch

This patch does the following:
1. create a new file status in HDFS, called HDFSFileStatus, for over-the-wire transfer, in
which the path contains only the local name of a path, not the full path. Also the path is
represented as is a byte array in Java UTF8 encoding just the same as the one stored in each
2. change ClientProtocol getListing to return HDFSFileStatus[] and getFileInfo to return HDFSFileStatus.

 a. The path in the return value of getFileInfo is always an empty byte array. 
 b. If listStatus is called on a file, the path in the only HDFSFileStatus returned also is
an empty byte array;
 c. If listStatus is called on a directory, the path in each HDFSFileStatus in the returned
array contains the local name of the directory entry.
3. FileSystem#getFileStatus and FileSystem#listStatus still see FileStatus which contains
the full path name.
4. Unit tests are added to TestFileStatus to verify the change.

> NameNode should not return full path name when lisitng a diretory or getting the status
of a file
> -------------------------------------------------------------------------------------------------
>                 Key: HDFS-946
>                 URL: https://issues.apache.org/jira/browse/HDFS-946
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Hairong Kuang
>             Fix For: 0.22.0
>         Attachments: HDFSFileStatus.patch, HDFSFileStatus.patch
> FSDirectory#getListring(String src) has the following code:
>       int i = 0;
>       for (INode cur : contents) {
>         listing[i] = createFileStatus(srcs+cur.getLocalName(), cur);
>         i++;
>       }
> So listing a directory will return an array of FileStatus. Each FileStatus element has
the full path name. This increases the return message size and adds non-negligible CPU time
to the operation.
> FSDirectory#getFileInfo(String) does not need to return the file name either.
> Another optimization is that in the version of FileStatus that's used in the wire protocol,
the field path does not need to be Path; It could be a String or a byte array ideally. This
could avoid unnecessary creation of the Path objects at NameNode, thus help reduce the GC
problem observed when a large number of getFileInfo or getListing operations hit NameNode.

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