As NoSQL DBs always prefer BASE over ACID.
Everyone always says that you can't have ACID when you are working with a NoSQL DBs.
For example, we have MongoDB (a popular NoSQL DB), which is hosted within a single server. No replicas. If the client app updates a document, strong consistency should take place.
(Just curious, not expert)
Yes, a write to a single instance, distributed database will be immediately consistent. You likely still won't have ACID, as each NoSQL variant has its own ways of handling (or not) atomicity.
Although, I have to wonder what the goal would be here. The main feature of a NoSQL database is its ability to support partition tolerance...which is lost in a single instance configuration. I can't think of many scenarios like that where I wouldn't just run Postgres.
Yes that's correct, inherently you end up with strong consistency because the use case is a single node server as opposed to a cluster.
Conversely there are RDBMS that offer consistency across multi-node clusters or quasi-hybrids of the BASE and ACID principals nowadays too.
Everything is fair game, there's a lot of blurred lines, and using NoSQL in a single server is pretty normal and will automatically offer consistency since there's nothing to replicate to.
What "Everyone" says isn't true!
A related issue was discussed on this forum recently ("If NoSQL stands for "Not only SQL", is SQL a subset of NoSQL?"), and in my answer, I mention 2 KV systems, one of which (RocksDB) has a subset of ACID transaction characteristics and one of which has them ALL (FoundationDB).
BTW, MongoDB is NOT fully ACID compliant - see the report from the highly respected JESPEN site here. There is further reading to be done here and here - but there is nothing to stop a system which fully supports SQL from being BASE and vice-versa...
And remember, don't believe everything a vendor tells you - they (ahem...) may be biased.
Also, don't forget that BASE is a perfectly valid strategy - for the likes of Amazon and/or Facebook where the odd cancelled order and/or lost post isn't going to be the end of the world - however, banks cannot (afford) to think like that - their systems have to be ACID - at least the ones handling financial transactions - maybe they perform their customer loyalty programmmes on a BASE system - lower machine specs and no requirement to maintain consensus/correctness leads to lower costs!
