HBase NoServerForRegionException？

Question

I am getting this exception when for a while i didn't communicated with HBase:

org.apache.hadoop.hbase.client.NoServerForRegionException: Timed out trying to locate root region because: Connection refused

is this something related with session expiry, if so, how can i extend session lifetime?

Answer 1

Query bin/hbase hbck and find in which machine root Regionserver is running..

You should get -ROOT- is okay on hbck. Make sure that all your Regionserver is up and running.

use start regionserver for starting regionserver

Answer 2

This error shows that the client is not able to talk to Region server. Check the region server associated with the region its trying to connect and check its up.

To identify the region server associated with the region please go through http://hbase.apache.org/0.94/book/regions.arch.html#regions.arch.assignment

Answer 3

Some factors have played a role here.

Please note the below steps which occur when you try to connect to Hbase from a client,

1. Hbase connects to Zookeeper to get the Ip of the regionservers which host the ROOT table.
2. The client caches this information about the IP's so that it doesnt have to contact the zookeeper again.

Your problem is that, your client is trying to connect to the zookeeper to get the IP. one of the below things may be going wrong,

1. Your client is not able to connect to the zookeeper.
2. The information about the ROOT contained inside the Znode in ZooKeeper is wrong.

Possible fixes.

1. Check if your zookeeper is working fine.

2. Delete the Znode for Hbase in your Zookeeper and restart the cluster. Don't worry, this wont delete your data.

Once this is achieved? the client can get the ROOT information and then query for the META table without any issue.

Answer 4

I don't think this has anything to do with session lifetime.

Check your cluster to make sure that it is up and working correctly and all region servers are alive. Then check the logs to make sure that they are not reporting some error state.

HBase is complex software -- without more detailed information it is very difficult to diagnose what is going on. And often you can discover the problem by collecting the more detailed information.