[jira] Updated: (HADOOP-1869) access times of HDFS files

["dhruba borthakur (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HADOOP-1869?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

dhruba borthakur updated HADOOP-1869:
-------------------------------------

    Attachment: accessTime1.patch

This patch does the following:

1. Implements access time for files. Directories do not have access times.
2. The access times of files is precise upto an hour boundary. This means that all accesses to a file between 2Pm and 2:59PM will have an access time of 2PM.
3. The transaction to write access time to edits is not synced. It is assumed that it will get synced as part of other transactions.
4. There is a configuration parameter to switch off access-times. By default, it is on.
5. There is a new FileSystem API setAccessTime() to set the access time on a file.
6. 

> 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.

-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.