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https://issues.apache.org/jira/browse/HADOOP-1869?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12625001#action_12625001
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Konstantin Shvachko commented on HADOOP-1869:
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A few preliminary comments.
# I agree we should better make INode.accessTimePrecision a configuration
parameter. In any case I did not expect it to be an extra field in INode (not
even static!!).
# If we introduce {{hdfs.access.time.precision}} as a config parameter, then
you do not need {{dfs.support.accessTime}} because you can either set
{{hdfs.access.time.precision}} to a big (unreachable) number or pick a special
value say "0" to indicate the atime should not be supported.
# {{FileSystem.setAccessTime()}} and related changes to client classes
including {{ClientProtocol}} seem to be redundant. We already have such method,
just call {{getBlockLocations()}}.
# In {{FSDirectory.setAccessTime()}} I would modify {{atime}} in memory every
time it's requested. This is free once you already have the INode. Only calling
of {{logAccessTime()}} should be done once an hour.
> 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
> Attachments: accessTime1.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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