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Comment by wll | Hacker News Reader

While that’s perfect to shield from orbital laser cannons, is active/active geo-independent replication possibile?

Well, if you want ACID then you are going to have to pay for at least one geographic round trip per committed transaction. (So why not go active/passive, and have at least one of your datacenters be fast?)

But what if you have different pieces of data and you want them to be fast in different datacenters? I think a great solution to this can be layered on top of multiple FoundationDB clusters, each using the satellite mode, but this is one thing that I at least haven't been able to think of a way to provide properly at the data model agnostic key/value store layer - the details about what to put where seem fundamentally dependent on your data model.

> So why not go active/passive, and have at least one of your datacenters be fast?

While local writes would stay fast, wouldn’t active/passive see higher-latency non-local writes than Spanner or Fauna’s (assuming a NAM-EUR-ASIA topology)?

I agree with and do appreciate the multiple FoundationDB clusters suggestion.

I'm speculating, but I think in this mode, from the "slow" datacenters you would see one round trip time to start a transaction, then reads will be fast (they can be done safely from your local datacenter because of MVCC), and then one round trip time to commit the transaction. I think that's as good as Spanner does with the same geography, but I'm not sure. I think you could get rid of the first round trip time even without any clock synchronization nonsense, by speculating on a read version for read/write transactions. And 1xRTT is obviously as fast as physically possible for ACID.

Update: Apparently Spanner is way slower than I thought in "slow" datacenters, doing a round trip for every transactional read. So this would absolutely stomp that. (Although spanner, as a higher level system, has the ability to move different data to be fast in different regions built in, which is nice, and as I said it will probably have to be a layer feature in the fdb world)

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