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From "Gary Helmling (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-15856) Cached Connection instances can wind up with addresses never resolved
Date Fri, 20 May 2016 19:37:13 GMT

     [ https://issues.apache.org/jira/browse/HBASE-15856?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Gary Helmling updated HBASE-15856:
----------------------------------
       Resolution: Fixed
    Fix Version/s: 1.1.6
                   0.98.20
     Release Note: During periods where DNS resolution was not available or not working correctly,
we could previously cache unresolved hostnames forever, in some cases preventing further connections
to these hosts even when DNS service was restored.  With this change, unresolved hostnames
will no longer be cached, and will instead throw an UnknownHostException during connection
setup.
           Status: Resolved  (was: Patch Available)

Committed to all active branches.  Thanks for reviews, [~yuzhihong@gmail.com] and [~saint.ack@gmail.com].

> 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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