select
fun select(configured: String, providers: Map<String, StoreProvider>, resources: StoreResources, memoryOptIn: String? = null): String
The store type configured, auto resolved by what is available: the one durable provider of providers that resources are enough for (StoreProvider.available: PostgreSQL with a DataSource bean, MongoDB with a MongoClient bean). Several available is ambiguous, and a type configured but unavailable fails.
None available fails too: a node in memory loses every committed fact when it stops, and two of them would each own every partition. Auto falls back to memory only with a memoryOptIn, the reason a development node may keep its data there (see memoryOptIn below); a node meant to run in memory names it, wow.backend=memory.