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From "ASF subversion and git services (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-2876) Unexpected looping from HdfsZooInstance.getInstanceID()
Date Mon, 09 Jun 2014 21:03:02 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-2876?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14025743#comment-14025743
] 

ASF subversion and git services commented on ACCUMULO-2876:
-----------------------------------------------------------

Commit 1a33f6df9c31d496f8260f785f85817ab6cb2b9c in accumulo's branch refs/heads/master from
[~bhavanki]
[ https://git-wip-us.apache.org/repos/asf?p=accumulo.git;h=1a33f6d ]

ACCUMULO-2876 Use site config to configure default VolumeManagerImpl

This changes VolumeManagerImpl.get() to use the site configuration instead of the
ZooKeeper-based system configuration. This seems to align better with what is intended,
and it also eliminates the risk of an infinite loop, where the system configuration
requires an HdfsZooInstance instance ID, which requires a volume manager.


> Unexpected looping from HdfsZooInstance.getInstanceID()
> -------------------------------------------------------
>
>                 Key: ACCUMULO-2876
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-2876
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: client
>    Affects Versions: 1.6.0
>            Reporter: Bill Havanki
>            Assignee: Bill Havanki
>            Priority: Minor
>
> While working ACCUMULO-2615, I encountered a weird looping behavior rooted at {{HdfsZooInstance.getInstanceID()}}
that seems to accidentally avoid a stack overflow. I'm a bit blocked at the moment on -2615
since my work exposed the loop.
> Here's a summary of the loop. The unit test {{SystemCredentialsTest}} in the tserver
module exercises it.
> * Start at {{HdfsZooInstance.getInstanceID()}}, which calls to an internal {{_getInstanceID()}}
the first time.
> * A volume manager is needed to find the instance ID in HDFS, so {{VolumeManagerImpl.get()}}
is called.
> * That call needs the "system" configuration, so a call to {{ServerConfiguration.getSystemConfiguration()}}
is made, passing the {{HdfsZooInstance}} object.
> * The system configuration is a {{ZooConfiguration}} object, and that is created from
{{ZooConfiguration.getInstance()}}.
> * That factory method creates a {{ZooConfiguration}} object, saved as a static field.
The code then tries to get the instance ID for the passed-in instance, which is the {{HdfsZooInstance}}
object. So we're back at the top of the loop.
> In the last step of the second iteration of the loop, the factory method sees that the
static field for the singleton instance of {{ZooConfiguration}} was set in the first iteration,
so it returns it and doesn't look for the instance ID. That stops the looping and the call
stack unwinds.
> (My refactoring work has trouble with this because it gets rid of the single static field
in favor of a map of objects keyed by instance ID.)
> This loop indicates a mutual dependency between configurations, the volume manager, and
{{HdfsZooInstance}} that should be resolved.



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