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https://issues.apache.org/jira/browse/HADOOP-1869?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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dhruba borthakur updated HADOOP-1869:
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Attachment: accessTime5.patch
Incorporated all of Konstantin's review comments other than the one that said
that setAccessTime() call should be removed.
The setAccessTime() call is a utility method that allows an application to set
the access time of a file without having to "open" the file. The
permission-access-checks are precisely the same as that for "opening" a file,
so there isn't any security concern IMO. Most file systems support setting
access times/modification times on a file, see
http://linux.die.net/man/2/utimes.
I purposely did not add a command to the FsShell to display access times. An
application can fetch the accessTime using a programmatic API
FileSystem.getFileStatus().
> 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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