Creation time and modification time for hadoop files and directories
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Key: HADOOP-1377
URL: https://issues.apache.org/jira/browse/HADOOP-1377
Project: Hadoop
Issue Type: New Feature
Reporter: dhruba borthakur
Assigned To: dhruba borthakur
This issue will document the requirements, design and implementation of
creation times and modification times of hadoop files and directories.
My proposal is to have support two additional attributes for each file and
directory in HDFS. The "creation time" is the time when the file/directory was
created. It is a 8 byte integer stored in each FSDirectory.INode. The
"modification time" is the time when the last modification occured to the
file/directory. It is an 8 byte integer stored in the FSDirectory.INode. These
two fields are stored in in the FSEdits and FSImage as part of the transaction
that created the file/directory.
My current proposal is to not support "access time" for a file/directory. It is
costly to implement and current applications might not need it.
In the current implementation, the "modification time" for a file will be same
as its creation time because HDFS files are currently unmodifiable. Setting
file attributes (e.g. setting the replication factor) of a file does not modify
the "modification time" of that file. The "modification time" for a directory
is either its creation time or the time when the most recent file-delete or
file-create occured in that directory.
A new command named "hadoop dfs -lsl" will display the creation time and
modification time of the files/directories that it lists. The output of the
existing command "hadoop dfs -ls" will not be affected.
The ClientProtocol will change because DFSFileInfo will have two additional
fields: the creation time and modification time of the file that it represents.
This information can be retrieved by clients thorugh the
ClientProtocol.getListings() method. The FileSystem public API will have two
additional methods: getCreationTime and getModificationTime().
The datanodes are completely transparent to this design and implementation and
requires no change.
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