Level expansion process
1, the expansion of primary shard and a replica shard will automatically load balancing
2, after expansion shard of each node is reduced, then assigned to each shard's cpu, memory, io will be more resources, improve performance
3, expansion of the limit, if there are six shard, expansion of the limit is six nodes, each node on a shard number if you want to go beyond the limits of expansion, such as the expansion to nine nodes, you can increase the replica shard of
4, 6 shard, 3 nodes, can withstand up to a few nodes where the server is down? (Fault tolerance) any server downtime will lose some data. In order to improve fault tolerance, increasing the number of shard: shard 9, (. 3 th primary shard, 6 th Replica shard), so that we can tolerate up to two servers is down
Summary: The expansion is to increase the throughput of the system, taking into account also fault tolerance, which is to get as many server downtime but also to ensure that data is not lost.