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From "Gary Helmling (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-15856) Cached Connection instances can wind up with addresses never resolved
Date Wed, 18 May 2016 21:55:12 GMT
Gary Helmling created HBASE-15856:
-------------------------------------

             Summary: 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


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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