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From "Philip Zeyliger (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HADOOP-8292) TableMapping does not refresh when topology is updated
Date Wed, 18 Apr 2012 23:46:39 GMT
TableMapping does not refresh when topology is updated

                 Key: HADOOP-8292
                 URL: https://issues.apache.org/jira/browse/HADOOP-8292
             Project: Hadoop Common
          Issue Type: Bug
    Affects Versions: 2.0.0
            Reporter: Philip Zeyliger

HADOOP-7030 introduced TableMapping, an implementation of DNSToSwitchMapping which uses a
file to map from IPs/hosts to their racks.  It's intended to replace ScriptBasedMapping for
cases where the latter was just a complicated way of looking up the rack in a file.

Though there was discussion of it on the JIRA, the TableMapping implementation is not 'refreshable'.
 i.e., if you want to add a host to your cluster, and that host wasn't in the topology file
to begin with, it will never be added.

TableMapping should refresh, either based on a command that can be executed, or, perhaps,
if the file on disk changes.

I'll also point out that TableMapping extends CachedDNSToSwitchMapping, but, since it does
no refreshing, I don't see what the caching gets you: I think the cache ends up being a second
copy of the underlying map, always.

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