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Choice of Consistency Model
Are we free to choose to use any consistency model covered in the lectures for our ECS design in M2 as long as we can justify the reason?
the students' answer,
where students collectively construct a single answerthe instructors' answer,
where instructors collectively construct a single answerI dont understand why consistency model is involved in ecs? the update of metadata is only managed by a single server, which is the ecs.
followup discussionsfor lingering questions and comments
Anonymous Scale
Wait so the ECS will just update the meta for each single server? why a consistency model is not involved?
Gengrui Zhang
why a CM needs to be involved at ECS? can you give me an example?
Anonymous Scale
When the ECS receives a request from a new server to join, the ECS will update the metadata and send it back to the new server and the data transfer process starts. A CM is needed to keep the metadata between different servers to be consistent?
Gengrui Zhang
All kv servers must have the same metadata. I wouldnt call this a CM. This should be a consensus. Since we assume ECS never fails, then the update should be able to be completed in a two-phase commit pattern.
Anonymous Scale
ohh i see. could you elaborate on what a two-phase commit pattern?
Gengrui Zhang
like a consensus instance in paxos; the ecs is a proposer, and the update has two phases: first phase: ask kv servers to apply the update; second phase: confirm the update with all kv servers.