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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1869) access times of HDFS files
Date Fri, 05 Sep 2008 05:59:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1869?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12628559#action_12628559
] 

dhruba borthakur commented on HADOOP-1869:
------------------------------------------

I created HADOOP-4077 to debate on the access permissions that are requires to invoke the
setTimes API.

The failed test is TestKosmosFileSystem and it has been failing for the last 5 builds. This
failure is not part of this patch.

The findbugs warnings are not introduced by this patch. I believe that the test-patch process
is getting confused while diffing the findbugs outout on trunk with the findbugs output from
this patch.

Konstantin has reviewed this patch earlier. Please let me know if somebody else wants to review
this patch. I would to get it commited by Friday Sept 5 so that it can make it into the 0.19
release.

> 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, accessTime6.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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