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https://issues.apache.org/jira/browse/ZOOKEEPER-832?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14560376#comment-14560376
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Germán Blanco commented on ZOOKEEPER-832:
-----------------------------------------
Hi [~ylopotun],
as far as I know there is no decision yet.
The proposed patch would solve your issue. In the proposed patch (if I remember
correctly) the client tries to connect to a different server of the cluster
until it either succeeds or finds the leader (or stand-alone server). If it
finds the leader and there zxid is still higher it just restarts the
connection. With an stand-alone server it will just immediately reconnect and
end the loop of connection retries.
The caveat is that something very wrong has happened (e.g. server lost all its
data) and the client should be notified of this problem an not just reset the
connection and continue. But on the other hand, every time that a client
reconnects this client cannot make any assumptions at all about what might have
happened with the data in that interval, so in my view this shouldn't be that
bad. In any case it is better than an endless loop (again in my opinion).
I think this is a good enough solution for now. If this issue is considered a
blocker, I would propose to go for that. If there are any positive comments on
that line, I will update the patch.
I tried to introduce a more elaborated solution back then, but I believe this
would need for me to provide a better explanation of why it would be good to
follow that path.
Regards to all,
/German
> Invalid session id causes infinite loop during automatic reconnect
> ------------------------------------------------------------------
>
> Key: ZOOKEEPER-832
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-832
> Project: ZooKeeper
> Issue Type: Bug
> Components: server
> Affects Versions: 3.3.1, 3.4.5, 3.5.0
> Environment: All
> Reporter: Ryan Holmes
> Assignee: Germán Blanco
> Priority: Blocker
> Fix For: 3.5.2, 3.6.0
>
> Attachments: ZOOKEEPER-832.patch, ZOOKEEPER-832.patch,
> ZOOKEEPER-832.patch, ZOOKEEPER-832.patch, ZOOKEEPER-832.patch
>
>
> Steps to reproduce:
> 1.) Connect to a standalone server using the Java client.
> 2.) Stop the server.
> 3.) Delete the contents of the data directory (i.e. the persisted session
> data).
> 4.) Start the server.
> The client now automatically tries to reconnect but the server refuses the
> connection because the session id is invalid. The client and server are now
> in an infinite loop of attempted and rejected connections. While this
> situation represents a catastrophic failure and the current behavior is not
> incorrect, it appears that there is no way to detect this situation on the
> client and therefore no way to recover.
> The suggested improvement is to send an event to the default watcher
> indicating that the current state is "session invalid", similar to how the
> "session expired" state is handled.
> Server log output (repeats indefinitely):
> 2010-08-05 11:48:08,283 - INFO
> [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn$Factory@250] -
> Accepted socket connection from /127.0.0.1:63292
> 2010-08-05 11:48:08,284 - INFO
> [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@751] - Refusing
> session request for client /127.0.0.1:63292 as it has seen zxid 0x44 our last
> zxid is 0x0 client must try another server
> 2010-08-05 11:48:08,284 - INFO
> [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@1434] - Closed
> socket connection for client /127.0.0.1:63292 (no session established for
> client)
> Client log output (repeats indefinitely):
> 11:47:17 org.apache.zookeeper.ClientCnxn startConnect INFO line 1000 -
> Opening socket connection to server localhost/127.0.0.1:2181
> 11:47:17 org.apache.zookeeper.ClientCnxn run WARN line 1120 - Session
> 0x12a3ae4e893000a for server null, unexpected error, closing socket
> connection and attempting reconnect
> java.net.ConnectException: Connection refused
> at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
> at
> sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:574)
> at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1078)
> 11:47:17 org.apache.zookeeper.ClientCnxn cleanup DEBUG line 1167 - Ignoring
> exception during shutdown input
> java.nio.channels.ClosedChannelException
> at
> sun.nio.ch.SocketChannelImpl.shutdownInput(SocketChannelImpl.java:638)
> at sun.nio.ch.SocketAdaptor.shutdownInput(SocketAdaptor.java:360)
> at
> org.apache.zookeeper.ClientCnxn$SendThread.cleanup(ClientCnxn.java:1164)
> at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1129)
> 11:47:17 org.apache.zookeeper.ClientCnxn cleanup DEBUG line 1174 - Ignoring
> exception during shutdown output
> java.nio.channels.ClosedChannelException
> at
> sun.nio.ch.SocketChannelImpl.shutdownOutput(SocketChannelImpl.java:649)
> at sun.nio.ch.SocketAdaptor.shutdownOutput(SocketAdaptor.java:368)
> at
> org.apache.zookeeper.ClientCnxn$SendThread.cleanup(ClientCnxn.java:1171)
> at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1129)
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