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From "Allen Wittenauer (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1869) access times of HDFS files
Date Wed, 03 Sep 2008 17:41:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1869?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12628068#action_12628068
] 

Allen Wittenauer commented on HADOOP-1869:
------------------------------------------

I think Konstantin's point is that the only "realistic" use case we can come up with for setting
an arbitrary access time is during a file create (such as expansion of an archive and a distcp),
therefore the API should reflect that use case since it keeps the number of routines small.
 Please correct me if I'm wrong.

To me, that sounds incredibly unclean.  It would better to allow for a separate utimes()-equivalent
API so that a) if there is a use case later, it can be covered and b) do we really want a
call that is two operations-in-one?



> access times of HDFS files
> --------------------------
>
>                 Key: HADOOP-1869
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1869
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: dfs
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>             Fix For: 0.19.0
>
>         Attachments: accessTime1.patch, accessTime4.patch, accessTime5.patch
>
>
> HDFS should support some type of statistics that allows an administrator to determine
when a file was last accessed. 
> Since HDFS does not have quotas yet, it is likely that users keep on accumulating files
in their home directories without much regard to the amount of space they are occupying. This
causes memory-related problems with the namenode.
> Access times are costly to maintain. AFS does not maintain access times. I thind DCE-DFS
does maintain access times with a coarse granularity.
> One proposal for HDFS would be to implement something like an "access bit". 
> 1. This access-bit is set when a file is accessed. If the access bit is already set,
then this call does not result in a transaction.
> 2. A FileSystem.clearAccessBits() indicates that the access bits of all files need to
be cleared.
> An administrator can effectively use the above mechanism (maybe a daily cron job) to
determine files that are recently used.

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