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https://issues.apache.org/jira/browse/HBASE-15856?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15294566#comment-15294566
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Gary Helmling commented on HBASE-15856:
---------------------------------------
Looks like this may have broken TestMasterFailover in branch-1 and older. I'm
taking a look at it. If I can't come up with a solution tonight, I'll revert
from those branches.
> Cached Connection instances can wind up with addresses never resolved
> ---------------------------------------------------------------------
>
> Key: HBASE-15856
> URL: https://issues.apache.org/jira/browse/HBASE-15856
> Project: HBase
> Issue Type: Bug
> Components: Client
> Reporter: Gary Helmling
> Assignee: Gary Helmling
> Priority: Critical
> Fix For: 2.0.0, 1.3.0, 1.2.2, 0.98.20, 1.1.6
>
> Attachments: HBASE-15856.001.patch, HBASE-15856.002.patch,
> HBASE-15856.003.patch
>
>
> During periods where DNS is not working properly, we can wind up caching
> connections to master or regionservers where the initial hostname resolution
> and the resolution is never re-attempted. This means that clients will
> forever get UnknownHostException for any calls.
> When constructing a BlockingRpcChannelImplementation, we instantiate the
> InetSocketAddress to use for the connection. This instance is then used in
> the rpc client connection, where we check isUnresolved() and throw an
> UnknownHostException if that returns true. However, at this point the rpc
> channel is already cached in the HConnectionImplementation map of stubs. So
> at this point it will never be resolved.
> Setting the config for hbase.resolve.hostnames.on.failure masks this issue,
> since the stub key used is modified to contain the address. However, even in
> that case, if DNS fails, an rpc channel instance with unresolved ISA will
> still be cached in the stubs under the hostname only key.
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