TableMapping does not refresh when topology is updated
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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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