The most interesting question is what this does to the architecture of the database software itself. A large part of the complexity in a database’s design involves providing fast persistence by carefully writing the information to a hard disk. The best databases have an elaborate caching structure for keeping the most requested data in RAM while writing all changes through to the hard disk.
Much of this elaborate caching forces database programmers to pay strict attention to the disk and double-check to ensure that the data is correct. The database first writes the data, then double-checks that it’s there. If the write was successful, the database commits the new information, otherwise it rolls back. This care, often called the ACID principles, state that a database’s operations must be Atomic, Consistent, Isolated, and Durable.
If all of the information is kept in RAM, the game changes. There’s no need to make sure that the RAM and the disk are consistent because there is no disk. The database designer’s job becomes easier and the database becomes faster still.
Wayner also teaches a course titled Storing Sensitive Information with MySQL — something anyone engineering web-based payment or identity systems should pay close attention too!