Paul Millar created ZOOKEEPER-2893:
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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:
{quote}
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)
~[zookeeper-3.4.6.jar:3.4.6-1569965]
at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1081)
~[zookeeper-3.4.6.jar:3.4.6-1569965]
{quote}
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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