[rystsov]

> Thus far, causal consistency has generally been limited to research projects ... MongoDB is one of the first commercial databases we know of which provides an implementation.

Cosmos DB provides session consistency (looks like an another name for causal consistency) at least since 2014 [1].

Cosmos DB's session guarantees [2]: consistent prefix, monotonic reads, monotonic writes, read-your-writes, write-follows-reads.

Mongo DB's causal consistency guarantees [3]: monotonic reads, monotonic writes, read-your-writes, write-follows-reads.

Doubt that four years later still qualities as one of the first.

[1] https://www.infoq.com/news/2014/08/microsoft-azure-documentd...

[2] https://docs.microsoft.com/en-us/azure/cosmos-db/consistency...

[3] https://docs.mongodb.com/manual/core/read-isolation-consiste...

[aphyr]

Causal and session are definitely similar, but I'm not entirely sure if causal implies consistent prefix, and conversely, I think causal miiight have stronger implications than just the intersection of MR, MW, RYW, and WFR. Because we weren't entirely certain whether we could make that claim regarding Cosmos, we opted to be conservative.

[rystsov]

I agree it's hard for me too to be precise about naming in academic sense. But this published paper "Writes: the dirty secret of causal consistency" says that both Cosmos DB and MongoDB have causal consistency so I don't know.. At least Cosmos DB and MongoDB provide the same guarantees for session/causal.

[Strongerpass]

.. but the post didn't say it was first. Not even the part you quoted.

[Boxxed]

Well, the quote you reference says, "one of the first," doesn't it?

[Volt]

"we know of"

[polskibus]

Was Cosmos DB tested by Jepsen?

[rystsov]

It's off-topic. But yes, Cosmos DB has rigorous tests[1] including Jepsen (a tool).

[1] https://twitter.com/dharmashukla/status/869104163510034432