enhance documentation with package upgrade description

[tomatolog]

enhance documentation with package upgrade description

[sanikolaev]

I've prepared this PR #1729

Can you please elaborate more on the gmcast.segment=20 approach: how can it be done in Manticore Search? What commands on what nodes and in what order should be executed?

[tomatolog]

The idea of the point 5 is to make separation of the old and new nodes at the cluster. That could be done by assign another gmcast.segment value for the new nodes.
I was sure that command

SET CLUSTER a GLOBAL 'gmcast.segment' = 20;

does that. However after test I see it returns error that gmcast.segment can not be changed in runtime. That means the node needs to join with this option set. However as we do not have command that remove node from cluster now such scenario looks not very friendly due to many manual steps:

• user should stop the node
• remove cluster property from the manticore.json to prevent node rejoin the cluster on start
• upgrade daemon package
• start the node
• after node started issue cluster join with the Galera options

join cluster CLUSTER_NAME at 'ADDRESS:PORT' 'gmcast.segment=20' as options

this way the new nodes will form another segment at the cluster and will not be selected as donor for old nodes and will not push index with the new format into the old daemons.

After all nodes got upgraded it could be better to remove gmcast.segment option to reduce possible clutter in the cluster management. That also could be done now only after node got stopped and manually edit manticore.json deleting the options property.

Maybe we should not to mention point 5 and suggest to upgrade the cluster via full cluster restart described at our manual