I have a single server cluster installation of MemSQL on Ubuntu 14 LTS. I am unable to connect to memsql on port 3306 but the cluster is running on port 9000. Looks like a leaf is down. When i tried to upgrade memsql to version 4.0.1 I got this error:-
Starting MemSQL Upgrade
Currently on state OfflineClusterUpgrade.Init
Currently on state OfflineClusterUpgrade.SnapshottingDatabases
Currently on state OfflineClusterUpgrade.OfflineClusterUpgradeFail
MemSQL node 8D84F89D6716F03A44EACB9E3AF6565FA76B9DE9 failed to upgrade: Could not connect to MemSQL node 8D84F89D6716F03A44EACB9E3AF6565FA76B9DE9. Is the MemSQL node online?
What can I do to bring MemSql up again?
The cluster manager provided the help on port 9000. Firstly it clearly showed the status of all nodes.
There was an alert icon clicking it showed the solution.
I ran the command
memsql-ops cluster-start
It caused the node to recover and start again. This is really good.
来源：https://stackoverflow.com/questions/31423480/memsql-leaf-down-on-single-server-cluster