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From "Paul Millar (JIRA)" <j...@apache.org>
Subject [jira] [Created] (ZOOKEEPER-2893) very poor choice of logging if client fails to connect to server
Date Thu, 07 Sep 2017 09:51:00 GMT
Paul Millar created ZOOKEEPER-2893:

             Summary: very poor choice of logging if client fails to connect to server
                 Key: ZOOKEEPER-2893
                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2893
             Project: ZooKeeper
          Issue Type: Bug
          Components: java client
    Affects Versions: 3.4.6
            Reporter: Paul Millar

We are using ZooKeeper in our project and have received reports that, when suffering a networking
problem, log files become flooded with messages like:
07 Sep 2017 08:22:00 (System) [] Session 0x45d3151be3600a9 for server null, unexpected error,
closing socket connection and attempting reconnect
java.net.NoRouteToHostException: No route to host
        at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method) ~[na:1.8.0_131]
        at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717) ~[na:1.8.0_131]
        at org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:361)
        at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1081) ~[zookeeper-3.4.6.jar:3.4.6-1569965]

Looking at the code that logs this message ({{ClientCnxn}}), there seems to be quite a few
problems here:
# the code logs a stack-trace, even though there is no bug here.  In our project, we treat
all logged stack-traces as bugs,
# if the networking issue is not fixed promptly, the log files is flooded with these message,
# The message is built using {{ClientCnxnSocket#getRemoteSocketAddress}}, yet in this case,
this does not provide the expected information (yielding {{null}}),
# The log message fails to include a description of what actually went wrong.

(Additionally, the code uses string concatenation rather than templating when building the
message; however, this is an optimisation issue)

My suggestion is that this log entry is updated so that it doesn't log a stack-trace, but
does include some indication why the connection failed.

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