Read repair for cassandra with quorum

Question

I need to understand on read-repair for Cassandra 3.0. For example, I have three nodes A, B & C. My replication factor is 3. Now, I wrote with Quorum, and it successfully wrote on Node A & B, so client will receive success but somehow data was not written on Node C (it was down, and hints throttle time elapsed).

I have not run manual repair and my read repair change is 0.1.

After, few days, my node A is down, leaving me with Node B & Node C. So if I issue a read query with quorum, will read repair always write data to node C and return to client successfully or there may be a scenario, where client can receive an error of "unable to achieve consistency level".

Answer 1

If 2 out of 3 replicas are up, then, the Quorum consistency will be achieved therefore the client will be able to read data. As one of the nodes doesn't have any data therefore, read repair will happen.

As per my understanding(I'm new in Cassandra), whenever a query is executed in Cassandra, the coordinator node checks if the desired number of replicas(requested consistency) are able to respond to the query. If it happens, then the client receives the most recent version of the data(timestamps of the data returned by each node is compared) and then that recent version is written over all the remaining replicas via read repair in case of mismatch.