In a 2 DC deployment, When we use the consistency serial for Light Weight Transactions, does Cassandra pick a DC as a master DC to serialize the transactions?
Does LWT pick a master DC when we have multi DC deployment?
@papishetty.praneeth_19978 There is no concept of master/slave in Cassandra. Cassandra also doesn't "serialize" LWTs.
The SERIAL consistency is used in the read part of the read-before-write to satisfy the condition for the lightweight transaction. It lets C* read the current version of the data and if it encounters a write for the data which is still in progress, it commits the data as part of the read before returning a result.
At SERIAL consistency, it does not enlist nodes from a "master" DC. Instead it reads from a QUORUM of nodes (regardless of the DC they belong to) in order to satisfy the request. Cheers!
That was my understanding too. I was confused when I saw high ClientRequestLatencies only in one region. If a write comes in to DC "A" with serial as a consistency instead of local_serial, it might hit the cross DC "B" and the same happens when a write comes to DC "B" . Ok let me pull some more metrics from the service side .
Thanks you very much for the reply .
5 People are following this question.
