Github user aarondav commented on the pull request:
https://github.com/apache/spark/pull/771#issuecomment-57513660
I talked with @JoshRosen for a second opinion, and we came to the
realization that fundamentally, the PersistenceEngine is just a persisted
KV-store, which maps String names to serialized Array[Byte]. The current API
that uses Application/Driver/WorkerInfos is nice for the Master's type safety
purposes, but not good for extensibility. Note, for instance, that
ApplicationInfo contains an ActorRef to the driver!
The proposal we came up with is to simplify PersistenceEngine to this API:
```scala
@DevelperApi
trait PersistenceEngine {
def persist(name: String, bytes: Array[Byte])
def unpersist(name: String)
def readPersistedData(): (Seq[(String, Array[Byte])]
def close() {}
}
```
And then
```
private[spark]
class MasterFailoverAgent(persistenceEngine: PersistenceEngine,
leaderElectionAgent: LeaderElectionAgent) {
def addApplication(app: ApplicationInfo) {
persist(name, serialize(app))
}
...
def readPersistedData(): (Seq[ApplicationInfo], Seq[DriverInfo],
Seq[WorkerInfo])
def stop() {}
}
```
Then the Master would invoke the StandaloneRecoveryModeFactory to get the
PersistenceEngine and LeaderElectionAgent, and then create a
MasterFailoverAgent to wrap them (or the StandaloneRecoveryModeFactory could
have a `final def` that does this).
This is very close to what you suggested earlier with the FailoverAgent --
the only difference is that it keeps this API as a construct of the Master,
built out of the much simpler APIs that the user has to implement in
StandaloneRecoveryModeFactory.
What are your thoughts?
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