Notes

Notes Background Already existing scheme used db query for replication Replication scheme was in such a way that any follower could query any other follower Due to this when they tried to implement RAFT there was a mismatch between the architecture and algorithm. So they decided to change the algorithm to implement in existing architecture. Problem Querying will not give you the term number meaning you don’t know if you’re pulling from the leader or not and if the log entries are correct or not....

Notes Runs in 2 phases - Phase 1 - get a promise from majority of servers Phase 2 - get a majority of servers to commit Two important rules Two numbers should be used to track the system Highest seen Highest accepted Majority will only happen if the values getting selected are happening at the same number It can’t be that one value got accepted at 1,v1 and another got accepted at 3,v1....

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....

Notes

Notes While reading a paper, also pay attention to the authors and why they encountered this problem. While replicating, there are 2 options for replication: Sending the input to the replicas Sending the changes to the replicas More often than not, sending the input is more performant and easier to do. VMware hypervisor is a binary translation hypervisor(Another hypervisor type is TRAP) Incase of this paper, not every single state(of the VM) is replicated, but only some key states are recorded and replayed(as the performance tradeoff is too much)....