RAFT Notes
What kind of system is RAFT? Exactly once/At least once/ At most once?
Two ways to approach this:
- Application layer is responsible for de-duplication and the command is just appended (albeit with the same ID).
- Consensus layer(RAFT) is responsible for checking duplicates.
Let the client handle ID generation instead of servers.
PAXOS Notes
Majority concept is for making sure that two different groups of systems cannot reach different consensus as two majorities will always overlap.
How is a value chosen(committed): Majority need to accept the value->Each server accepts the first value it sees->Obvious problem that each server accepts its own value->Each server can accept multiple values->Obvious problem that multiple majorities->Strict rule that ensures that if there are multiple majorities then there values must be the same->If one value is chosen and other value is accepted then it means that they are same values->If one value is chosen and other value is proposed(proposal accepted) then that means they are same values->If one value is possibly chosen and other is proposed then make sure either the first one is never chosen or it is again proposed.