Look at the log time. 

The namenode  is already switching. 

ZKFC log Is written after the namenode is swiched. 



1.  Something?  What happened? The log does not record.

2.  2014-08-01 04:21:03,608   HA switching 

3.  2014-08-01 04:21:03,601   Zookeeper session timeout 

4.  2014-08-01 04:21:03,728   Namenode shutdown 

5.  2014-08-01 04:21:03,703   Zookeeper session disconnected  



-----Original Message-----
From: "Gordon Wang"<gwang@pivotal.io>
To: <user@hadoop.apache.org>; "cho ju il"<tjstory@kgrid.co.kr>;
Sent: 2014-08-01 (금) 15:44:59
Subject: Re: Why does suddenly ha switching?

From the log, looks like the connections between NameNodes and ZK quorum are not stable. And the ZK session is time-out. You can check the log of the Zookeeper servers. You may find some errors about the connection failure.

On Fri, Aug 1, 2014 at 2:06 PM, cho ju il <tjstory@kgrid.co.kr> wrote:

Why does suddenly ha switching?

My hadoop cluster HA active namenode(host1) suddenly switch to standby namenode(host2).

I could not found any error in hadoop logs (in any server) to identify the root cause.

Tthe Namenodes following error appeared in hdfs logs frequently and non of the application could read the HDFS files.

*** namenode log

2014-08-01 04:20:39,133 INFO org.apache.hadoop.hdfs.server.blockmanagement.CacheReplicationMonitor: Rescanning after 30000 milliseconds

2014-08-01 04:20:39,151 INFO org.apache.hadoop.hdfs.server.blockmanagement.CacheReplicationMonitor: Scanned 0 directive(s) and 0 block(s) in 19 millisecond(s).

2014-08-01 04:21:03,608 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: Stopping services started for active state

2014-08-01 04:21:03,728 INFO org.apache.hadoop.hdfs.server.namenode.NameNode: SHUTDOWN_MSG:

*** zkfc log

2014-08-01 04:21:03,601 INFO org.apache.zookeeper.ClientCnxn: Client session timed out, have not heard from server in 46910ms for sessionid 0x147000ee1f70137, closing socket connection and attempting reconnect

2014-08-01 04:21:03,703 INFO org.apache.hadoop.ha.ActiveStandbyElector: Session disconnected. Entering neutral mode...


Gordon Wang