Adapters allow us to persist events (for the write model) and/or projections (for the read model).
If you can't find an adapter for your favorite database, you can build one by implementing the Adapter Interface.
The Adapter Interface has two sets of methods, depending if you are persisting events, projections, or both. Not every database is suitable for storing both. DynamoDB, for example, is very well suited for storing events, but lacks the search capabilities which are useful when storing projections. ElasticSearch, on the other hand, is great for storing, and searching, arbitrary JSON objects (projections) but is not very well suited for a stack of events.
When implementing the Adapter Interface, you can choose which set of methods to implement.