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the pcf mysql product is based on the oss cf mysql . for each bosh deployment of mysql you get a mysql compatible cluster. the cluster uses mariadb and galera for the database nodes. the default configurations for tunable parameters are listed in the spec file:
what those values should be for your deployment and application workloads are going to be highly dependent on what tradeoffs you want to make. the service plan you use should indicate the number of connections available with your plan, and how you configure max connections in your application typically depends on the database access framework you use.