How-to: resolve hbase "org.apache.hadoop.hbase.TableExistsException: hbase:namespace"

启动hbase时，在日志里发现如下错误：

Error:
2015-06-24 13:34:05,251 FATAL [master:60000.activeMasterManager] master.HMaster: Failed to become active master
org.apache.hadoop.hbase.TableExistsException: hbase:namespace
at org.apache.hadoop.hbase.master.handler.CreateTableHandler.checkAndSetEnablingTable(CreateTableHandler.java:152)
at org.apache.hadoop.hbase.master.handler.CreateTableHandler.prepare(CreateTableHandler.java:125)
at org.apache.hadoop.hbase.master.TableNamespaceManager.createNamespaceTable(TableNamespaceManager.java:233)
at org.apache.hadoop.hbase.master.TableNamespaceManager.start(TableNamespaceManager.java:86)
at org.apache.hadoop.hbase.master.HMaster.initNamespace(HMaster.java:897)
at org.apache.hadoop.hbase.master.HMaster.finishActiveMasterInitialization(HMaster.java:739)
at org.apache.hadoop.hbase.master.HMaster.access$500(HMaster.java:169)
at org.apache.hadoop.hbase.master.HMaster$1.run(HMaster.java:1479)
at java.lang.Thread.run(Thread.java:745)
2015-06-24 13:34:05,255 FATAL [master:60000.activeMasterManager] master.HMaster: Master server abort: loaded coprocessors are: []
2015-06-24 13:34:05,256 FATAL [master:60000.activeMasterManager] master.HMaster: Unhandled exception. Starting shutdown.
org.apache.hadoop.hbase.TableExistsException: hbase:namespace
at org.apache.hadoop.hbase.master.handler.CreateTableHandler.checkAndSetEnablingTable(CreateTableHandler.java:152)
at org.apache.hadoop.hbase.master.handler.CreateTableHandler.prepare(CreateTableHandler.java:125)
at org.apache.hadoop.hbase.master.TableNamespaceManager.createNamespaceTable(TableNamespaceManager.java:233)
at org.apache.hadoop.hbase.master.TableNamespaceManager.start(TableNamespaceManager.java:86)
at org.apache.hadoop.hbase.master.HMaster.initNamespace(HMaster.java:897)
at org.apache.hadoop.hbase.master.HMaster.finishActiveMasterInitialization(HMaster.java:739)
at org.apache.hadoop.hbase.master.HMaster.access$500(HMaster.java:169)
at org.apache.hadoop.hbase.master.HMaster$1.run(HMaster.java:1479)
at java.lang.Thread.run(Thread.java:745)
2015-06-24 13:34:05,256 INFO [master:60000.activeMasterManager] regionserver.HRegionServer: STOPPED: Unhandled exception. Starting shutdown.

原因：由于hbase非正常启动，在zookeeper上没有把相应的/hbase节点注销，所以再次启动会报上面的错。解决方案：
登录zookeeper，删除/hbase节点。

[root@centOS1 conf]# zkCli.sh
[zk: localhost:2181(CONNECTED) 9] ls /
[hadoop-ha, hbase, zookeeper]
[zk: localhost:2181(CONNECTED) 11] delete /hbase
Node not empty: /hbase
[zk: localhost:2181(CONNECTED) 12] rmr /hbase
[zk: localhost:2181(CONNECTED) 13] ls /
[hadoop-ha, zookeeper]