[
https://issues.apache.org/jira/browse/HADOOP-1869?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12623758#action_12623758
]
Raghu Angadi commented on HADOOP-1869:
--------------------------------------
> However, how will the namenode remember which inodes are dirty and need to be
> flushed?
It does not need any more structures than what you have proposed ("Add a 4 byte
field to the in-memory inode to maintain access time."). So at each access, you
check if this 4-byte field is older than "accuracy setting", then you add a
EditLog entry. If you want to keep the in-memory accurately (which I don't
think is required), then you need to add 4 bytes more to record "last logged
time". Right?
> 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
>
> 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.
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
