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0 pointsthrow935y ago0 comments

>> Let's say that their consistency model is achieved via quorum, that is writes write to a quorum of nodes while reads read from a quorum of nodes (of their metadata database) then this guarantees read after write consistency.

If reads are reading only from a quorum of nodes how do you guarantee they have latest data? In theory, while a node is servicing a read request wouldn’t you need to query “all” other nodes to verify that the data in current node is latest? What if the quorum of nodes don’t have the latest data yet?

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YZF5y ago

You write to a quorum of nodes and you read from a quorum of nodes. Latest is determined by a clock. Let's say you wrote to 2 out of 3 nodes, and read from 2 out of 3 nodes, one of those 2 you read from is going to have the latest data. This is how consistency works in Cassandra e.g.

There are other models, for example by using a consensus protocol.

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