The too many connections error is caused when flex.bi is trying to make too many connections to the database. The reason for this is that you have either specified too many allowed connections in the flex.bi connection pool or you have set your max_connections database parameter too low.
The pool parameter is specified within the dlexbi_private/config/database.toml with the following parameter:
pool = "200"
What is important to remember is that the "pool" parameter specifies the amount of connections for both flex.bi and Mondrian, so if you set the "pool" parameter to 200 then you will have to allow at least 400 connections to the database.
To specify the amount of allowed database connections adjust the following parameters in your database:
max_connections = 450 #MySQL and PostgreSQL
Then restart your database and these errors should be resolved.