Which cluster DB(mysql or postgres) for nextcloud and proxy for speed

I planned two server srvA and srvB cluster database for nextcloud13. On srvA also planned proxy(read from both server, srvA and srvB).

A few questions:

  1. which database will be quicker(and how many % will be diff), mysql or postgres for that scenario?
  2. will proxy help in performance. Idea is, that proxy read querrys from both servers simultanious.
    3.if add 3rd srvC,in cluster and proxy, is this add performance and how many?

Database cluster work with 3 servers or +. With two servers erevy time you have a crash/reboot your cluster is break and need a manual recovery :wink: #BrainSplit

You win (scalability, no gain for a single user) only with read request. For write request you loose perf (each request need be reparted on full cluster node).
When the client sends a write request, the transaction must be done on all nodes before being reported as OK to the client.