前階段同事遷移Zookeeper（是給Kafka使用的以及flume使用）后發現所有Flume-producer/consumer端集體報錯：

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07?Jan?2014?01:19:32,571?INFO? [conf-file-poller-0-SendThread(xxx:2181)] (org.apache.zookeeper.ClientCnxn$SendThread.startConnect:1058)? - Opening socket connection to server xxx:2181 07?Jan?2014?01:19:32,572?INFO? [conf-file-poller-0-SendThread(xxx:2181)] (org.apache.zookeeper.ClientCnxn$SendThread.primeConnection:947)? - Socket connection established to xxx:2181, initiating session 07?Jan?2014?01:19:32,573?INFO? [conf-file-poller-0-SendThread(xxx:2181)] (org.apache.zookeeper.ClientCnxn$SendThread.run:1183)? - Unable to read additional data from server sessionid?0x142f42b91871911, likely server has closed socket, closing socket connection and attempting reconnect 07?Jan?2014?01:19:32,845?INFO? [conf-file-poller-0-SendThread(xxx:2181)] (org.apache.zookeeper.ClientCnxn$SendThread.startConnect:1058)? - Opening socket connection to server xxx:2181

一直在不斷的重試連接失敗再重試，問同事說：網路連通性早就驗證過，然后查看server端日志發現：

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2014-01-06?23:59:59,987?[myid:1] - INFO? [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxnFactory@197] - Accepted socket connection from /xxx:45282 2014-01-06?23:59:59,987?[myid:1] - WARN? [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:ZooKeeperServer@793] - Connection request from old client xxx:45282; will be dropped?if?server is in r-o mode 2014-01-06?23:59:59,987?[myid:1] - INFO? [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:ZooKeeperServer@812] - Refusing session request?for?client xxx:45282?as it has seen zxid?0x60fd15564?our last zxid is?0x10000000f?client must?try?another server 2014-01-06?23:59:59,987?[myid:1] - INFO? [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@1001] - Closed socket connection?for?client xxx:45282?(no se ssion established?for?client) 2014-01-06?23:59:59,989?[myid:1] - INFO? [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxnFactory@197] - Accepted socket connection from xxx:45285

發現Flume還是保留原來的zxid，但是現在的zxid竟然是0，所以拋出異常！

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if?(connReq.getLastZxidSeen() > zkDb.dataTree.lastProcessedZxid) { ????????????String msg =?"Refusing session request for client " ????????????????+ cnxn.getRemoteSocketAddress() ????????????????+?" as it has seen zxid 0x" ????????????????+ Long.toHexString(connReq.getLastZxidSeen()) ????????????????+?" our last zxid is 0x" ????????????????+ Long.toHexString(getZKDatabase().getDataTreeLastProcessedZxid()) ????????????????+?" client must try another server"; ????????????LOG.info(msg); ????????????throw?new?CloseRequestException(msg); ????????}

? ?后來問同事是怎么做的遷移：先啟動一套新的集群，然后關閉老的集群，同時在老集群的一個IP：2181起了一個haproxy代理新集群以為這樣，可以做到透明遷移=。=，其實是觸發了ZK的bug-832導致不停的重試連接，只有重啟flume才可以解決

? ?正確的遷移方式是，把新集群加入老集群，然后修改Flume配置等一段時間（flume自動reconfig）后再關閉老集群就不會觸發這個問題了.

本文轉自MIKE老畢 51CTO博客，原文鏈接：http://blog.51cto.com/boylook/1365364，如需轉載請自行聯系原作者

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