zookeeper的maxSessionTimeout默认值导致hbase regionserver超时
在hbase中经常会遇到regionserver挂掉的情况，查看日志会看到这样的错误信息
2016-02-16 11:51:24,882 WARN [master/hadoop02/192.168.100.5:6000] zookeeper.ZKUtil: master:6000-0x3525df55101a556, quorum=hadoop02:2181,hadoop03:2181,hadoop01:2181, baseZNode=/hbase Unable to get data of znode /hbase/xx
org.apache.zookeeper.KeeperException$SessionExpiredException: KeeperErrorCode = Session expired for /hbase/xx
at org.apache.zookeeper.KeeperException.create(KeeperException.java:127)
at org.apache.zookeeper.KeeperException.create(KeeperException.java:51)
at org.apache.zookeeper.ZooKeeper.getData(ZooKeeper.java:1155)
at org.apache.hadoop.hbase.zookeeper.RecoverableZooKeeper.getData(RecoverableZooKeeper.java:359)
at org.apache.hadoop.hbase.zookeeper.ZKUtil.getData(ZKUtil.java:745)
说明与zookeeper的连接的session超时了，可是在hbase-site.xml中设置了zookeeper的超时时间为2分钟，原来
zookeeper中自带两个参数设置了session的超时时间，在启动时日志中会显示
2016-02-16 11:39:49,164 - INFO [main:QuorumPeer@992] - tickTime set to 2000
2016-02-16 11:39:49,165 - INFO [main:QuorumPeer@1012] - minSessionTimeout set to -1
2016-02-16 11:39:49,165 - INFO [main:QuorumPeer@1023] - maxSessionTimeout set to -1
而minSessionTimeout 和maxSessionTimeout 是用下面的方式算出来的
public int getMinSessionTimeout()
{ return minSessionTimeout == -1 ? tickTime * 2 : minSessionTimeout; }
public int getMaxSessionTimeout()
{ return maxSessionTimeout == -1 ? tickTime * 20 : maxSessionTimeout; }
默认情况，tickTime=2sec，那么minSessionTimeout 和 maxSessionTimeout 分别是4sec和40sec
所以在hbase中设置超时时间是没用的，必须修改zookeeper自身的maxSessionTimeout为1200000，才能真正起到加长zookeeper的session超时时间的作用