Database for Camunda

Hello,

Please provide below information or a thread if it was already discussed in this forum.

What is the recommended back-end database by Camunda between mySQL and SQL server ?
What are the challenges with Camunda -mysql and Camunda -SQL if any?
Is two database approach with Camunda recommended ? Like Camunda on SQL server or mySQL and application database on MongoDB /Oracle DB.

Please advice.

Regards,
SG