Big/small number of master nodes - downsides/advantages


(Michal Wegorek) #1

There is a config option allowing to set the number of master nodes in
ES installation:

  • discovery.zen.minimum_master_nodes

Q1) Lets say I have N nodes in total in the system. What are the
advantages/disadvantages of having the number of master nodes set to
1, N/2, N

  • I suspect master node is keeping the copy of all indices (contrary
    to slave node) in the cluster, so is it just a matter of space being
    used?

Q2) If minimum_master_nodes is set to M, and there are N (N < M) nodes
alive case some of them went down, will ES refuse to serve index/
search requests?

Q3) Does master node need more memory than slave node, if simplified,
can we say the number of memory needed is proportional to size of
indices stored in local space? Example:
Lets say there is 1 index in 5 shards in the system:

  • one of slaves is keeping shard1 and shard2 and needs 1G mem
  • one of masters is keeping shard[1-5], will it need aprox. 2.5G?

Thanks,
Michal.


(system) #2