[jira] Commented: (HADOOP-1869) access times of HDFS files

["Owen O'Malley (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-1869?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12627894#action_12627894 ] 

Owen O'Malley commented on HADOOP-1869:
---------------------------------------

Just to add noise to the fire, I'm +1 to setAccessTime. I also think it is a very good idea to be able to configure it off at the namenode. My case for setAccessTime is that if you expand an archive or do distcp, it is really nice to be able to optionally set all of the times to match the copied files. That includes access time.

> 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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