We have temporal workflow running backed by mysql. We are in the process of moving our systems from mysql to postgres!
There is no official db migration path currently and it’s something that will be improved on in the future.
Currently you would have to build a new cluster and configure its namespace to replicate the new one, then fail over to the new cluster followed by updating the namespace to remove the old cluster from it and finally decommission the old cluster. It’s not an easy task atm.