FAQ
NameNode should not return full path name when lisitng a diretory or getting the status of a file
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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


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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postedFeb 3, '10 at 8:41p
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