Ideas are needed to use the three databases in parallel. Assume that all three of them will be consistent after 'x' units of time. Some of them are:
Use other two as backups. Each of them can have backups of their own.
Distribute data among them. E.g. write for 1 database, read for another, etc.
Use them all via load balancing and distribute them geographically.
Having three variations of database and possibly more in future is a nice thing to have. This way we are not dependent on any merchant and our code is as generic as it can be.
Ideas are needed to use the three databases in parallel. Assume that all three of them will be consistent after 'x' units of time. Some of them are:
Having three variations of database and possibly more in future is a nice thing to have. This way we are not dependent on any merchant and our code is as generic as it can be.