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From "Christopher Tubbs (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-1771) Instance id and version info only stored on one hdfs instance
Date Wed, 18 Dec 2013 23:03:08 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-1771?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13852269#comment-13852269
] 

Christopher Tubbs commented on ACCUMULO-1771:
---------------------------------------------

Federation doesn't solve the problem. Accumulo can be configured with multiple logical filesystems
to use (called volumes). Whether they are actually separate namenodes, separate directories
on a single namenode, federated, or not, from Accumulo's perspective, it sees them as separate
volumes. It doesn't care about implementation.

So, the issue is that currently, the instance id and data version are stored only on one of
these volumes. But, we really need it stored across all of them, including any added later,
so that volumes can be removed or so that volumes can be reordered in the configuration without
breaking.

The only time this isn't an issue is if you configure Accumulo to use a single volume (which
may actually be configured as multiple filesystems... but Accumulo doesn't care about that.)

So, no, HDFS Federation does not solve the issue. Even if HDFS Federation provided a single
URI to refer to the entire logical filesystem (it doesn't; you still have separate URIs for
separate namenodes, or you use separate viewfs URIs as aliases to those separate namenodes),
it still wouldn't be good enough, because Accumulo could still be configured with this federated
HDFS, *and* an entirely separate logical filesystem.

> Instance id and version info only stored on one hdfs instance
> -------------------------------------------------------------
>
>                 Key: ACCUMULO-1771
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-1771
>             Project: Accumulo
>          Issue Type: Sub-task
>          Components: master, tserver
>            Reporter: Keith Turner
>            Priority: Critical
>             Fix For: 1.6.0
>
>
> When instance.volumes contains multiple uris only the first one is initialized with the
data version and instance id.   If the user changes the order of the uris in the config, it
seems like Accumulo will stop working correctly.



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