Currently we are using ElasticSearch 1.7.1, we have planned to upgrade to 2.3.1 and we have done all of the steps as mentioned in the ES 2.3.1 upgrading help documentations.
After we initiated the upgrade, 2.3.1 cluster started and nodes are connected properly, but pending_tasks are increasing consistently. It took more than 4 hours, but still pending_tasks are increasing and those tasks are refresh-mapping [index] fyi.
If anyone done the upgrade to 2.3.1or 2.x versions then can anyone please share your experience about this? Its an usual behaviour?
P.S : We dont have any special configurations in our config file, except basic changes like clustername, nodename, path to logs & data, network.host, unicast nodes.