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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-13946) Document how HDFS updates timestamps in the FS spec; compare with object stores
Date Mon, 09 Jan 2017 18:19:59 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-13946?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15812450#comment-15812450
] 

Chris Nauroth commented on HADOOP-13946:
----------------------------------------

bq. creation time? That of mkdir()?

I think I'm confused by the mentions of creation time.  We have mtime and atime in {{FileStatus}}.
 AFAIK, the inode data structures in the NameNode don't track a separate notion of creation
time, just mtime and atime.  Is there something I've missed?

bq. what operations on child entries update the modtime? mkdir, create, delete, rename. And
which don't?

Yes, and to this please also add concat.

bq. chmod and set time calls?

chmod (and setacl) and setTimes do not alter any modification times, neither on the target
path itself nor its parent.

> Document how HDFS updates timestamps in the FS spec; compare with object stores
> -------------------------------------------------------------------------------
>
>                 Key: HADOOP-13946
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13946
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: documentation, fs
>    Affects Versions: 2.7.3
>            Reporter: Steve Loughran
>            Assignee: Steve Loughran
>            Priority: Minor
>             Fix For: 2.8.0, 3.0.0-alpha2
>
>         Attachments: HADOOP-13946-001.patch, HADOOP-13946-002.patch
>
>
> SPARK-17159 shows that the behavior of when HDFS updates timestamps isn't well documented.
Document these in the FS spec.
> I'm not going to add tests for this, as it is so very dependent on FS implementations,
as in "POSIX filesystems may behave differently from HDFS". If someone knows what happens
there, their contribution is welcome.



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