Major Description
1) For each zk dump, currently hbase will create a zk client instance every time.
This is quite slow when any machines in the quorum is dead. Because it will connect to each machine in the zk quorum again.
<code>
HMaster master = (HMaster)getServletContext().getAttribute(HMaster.MASTER);
Configuration conf = master.getConfiguration();
HBaseAdmin hbadmin = new HBaseAdmin(conf);
HConnection connection = hbadmin.getConnection();
ZooKeeperWatcher watcher = connection.getZooKeeperWatcher();
</code>
So we can simplify this:
<code>
HMaster master = (HMaster)getServletContext().getAttribute(HMaster.MASTER);
ZooKeeperWatcher watcher = master.getZooKeeperWatcher();
</code>
2) Also when hbase call getServerStats() for each machine in the zk quorum, it hard coded the default time out as 1 min.
It would be nice to make this configurable and set it to a low time out.
When hbase tries to connect to each machine in the zk quorum, it will create the socket, and then set the socket time out, and read it with this time out.
It means hbase will create a socket and connect to the zk server with 0 time out at first, which will take a long time.
Because a timeout of zero is interpreted as an infinite timeout. The connection will then block until established or an error occurs.
3) The recoverable zookeeper should be real exponentially backoff when there is connection loss exception, which will give hbase much longer time window to recover from zk machine failures.