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From "Sameer Paranjpye (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1377) Creation time and modification time for hadoop files and directories
Date Fri, 22 Jun 2007 21:59:26 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1377?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12507526

Sameer Paranjpye commented on HADOOP-1377:

No, I don't have a particularly compelling use case for creation date. It can be dispensed
with. Creation time isn't even POSIX, from 'man 2 stat'

#     The time-related fields of struct stat are as follows:
#     st_atime     Time when file data last accessed.  Changed by the mknod(2),
#                 utimes(2) and read(2) system calls.
#     st_mtime     Time when file data last modified.  Changed by the mknod(2),
#                  utimes(2) and write(2) system calls.
#     st_ctime     Time when file status was last changed (inode data modifica-
#                  tion).  Changed by the chmod(2), chown(2), link(2),
#                  mknod(2), rename(2), unlink(2), utimes(2) and write(2) sys-
#                  tem calls.

We can implement something like, st_ctime later. It might be useful to have for accounting
when we have users and permissions.

> Creation time and modification time for hadoop files and directories
> --------------------------------------------------------------------
>                 Key: HADOOP-1377
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1377
>             Project: Hadoop
>          Issue Type: New Feature
>          Components: dfs
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>             Fix For: 0.14.0
>         Attachments: 1377-noctime.patch, 1377.patch, CreationModificationTime.html, CreationTime8.patch
> 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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