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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5908) Change AclFeature to capture list of ACL entries in an ImmutableList.
Date Wed, 26 Feb 2014 16:15:20 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5908?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13913081#comment-13913081
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Chris Nauroth commented on HDFS-5908:
-------------------------------------

Thank you for the review, Haohui.  I'm going to commit this.

bq. I wonder, do you have any plans to make similar changes on the methods in {{AclTransformation}}?

I think there is less reason to use {{ImmutableList}} inside {{AclTransformation}}.  For the
input ACL spec, the first thing we need to do is sort the entries so that the rest of the
algorithms can assume the ordering.  Right now, we do that as an in-place sort on the list
parsed from the protocol, so it's convenient for that to remain mutable.  For the output calculated
ACL, it's always the full logical ACL.  For the physical storage, we always end up unpacking
a few of those entries for mapping onto the permission bits, and the final list stored in
the {{AclFeature}} is a different, smaller list.  I think the change is really important inside
{{AclStorage}} and {{AclFeature}} though to guarantee that there is no accidental mutation
of an ACL associated to an existing inode.

BTW, I just learned that the Guava immutable collections have a smaller memory footprint than
the typical JDK data structures:

https://code.google.com/p/memory-measurer/wiki/ElementCostInDataStructures

That's a nice side benefit of this patch, and it's worth considering for future changes in
areas that consume a lot of memory.

> Change AclFeature to capture list of ACL entries in an ImmutableList.
> ---------------------------------------------------------------------
>
>                 Key: HDFS-5908
>                 URL: https://issues.apache.org/jira/browse/HDFS-5908
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 3.0.0
>            Reporter: Chris Nauroth
>            Assignee: Chris Nauroth
>            Priority: Minor
>         Attachments: HDFS-5908.1.patch
>
>
> After an {{AclFeature}} has been attached to an inode, its ACL entries must be immutable.
 We can enforce this in the type system more strongly by storing the entries in an {{ImmutableList}}
and changing the getter to return that type instead of raw {{List}}.



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