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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1869) access times of HDFS files
Date Thu, 28 Aug 2008 23:41:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1869?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12626791#action_12626791
] 

Raghu Angadi commented on HADOOP-1869:
--------------------------------------


I don't know how FileStatus, blockSize etc matters. I would have thought it would be something
like {{FileSystem.utimes(path, modTime, aTime)}} and keep the behaviour as close to as possible
to posix man page, just like FileSystem.setAccessTime() interface you added.

I suggested the name utimes() since you gave utimes() as the justification. If you think setAccessTime()
should be the name, not much I can do. 

The API stuff could better done in a different jira IMHO. 


> 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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