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https://issues.apache.org/jira/browse/HADOOP-1869?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12626680#action_12626680
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Konstantin Shvachko commented on HADOOP-1869:
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This is what I get from the discussion above.
- touch() method is useful and can find immediate application in fuse.
- for archival and (remote) copy purposes we will need a flag that would create
new files with time (and may be other) attributes having THE SAME value as the
source files.
- there is no reasonable use case for setAcessTime method at the moment. I mean
nobody needs to set aTime to yesterday or tomorrow unless it is the time of the
file being copied or untared.
In the spirit of _minimizing impact on external APIs_ I propose to
# introduce {{FileSystem.touch()}} and implement it in HDFS as a call to
getBlockLocations().
# not introduce setAcessTime() anywhere in hdfs client code including
ClientProtocol.
We can always introduce setAcessTime() when it will really be necessary.
Because once introduced its hard to take it back.
> 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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