One of the slides in Chapter 19. Caching video "Caching Exam Tips" says "If you see "in-memory database", that should make you think of 2 solutions: Redis and DynamoDB. If the scenario offers DynamoDB, pick that".
I don’t think DynamoDB offers an "in-memory database", so probably it should say "If you see "NoSQL database", that should make you think of 2 solutions: Redis and DynamoDB. If the scenario offers DynamoDB, pick that". Or do I miss something here?
If you check the official page for DynamoDB you see this under how it works "DynamoDB offers built-in security, continuous backups, automated multi-region replication, in-memory caching, and data export tools."
In the command line options you have the option -inMemory – DynamoDB runs in memory instead of using a database file (See https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DynamoDBLocal.UsageNotes.html"
You can also check "In-Memory Acceleration with DynamoDB Accelerator (DAX)"