Github user liyichao commented on the issue:
https://github.com/apache/spark/pull/18084
Hi, I've thought more thoroughly about this.
The main state involved here is Master.workers, Master.idToWorker, and
WorkerInfo.drivers. Say `driverId1` runs on Worker A. Assume A is network
partitioned, master calls removeWorker which set the worker's state to DEAD,
and remove the worker from persistenceEngine, but does not remove it from
Master.workers. Then launch the driver on Worker B.
When A reconnects, it will reregister to master, then master will remove
the old WorkerInfo (whose `drivers` field is not empty), and add a new
WorkerInfo (say `wf_A`), whose drivers are empty. After registered, the worker
then re-sync state with master by sending `WorkerLatestState` with a
`driverId1`, the master does not find it in `wf_A.drivers`, so it asks worker A
to kill it. After killed the driver, worker A sends
`DriverStateChanged(driverId1, DriverState.KILLED)`, the master then mistakenly
removes `driverId1`, which now runs on worker B.
How to recognize the `DriverStateChanged` come from worker A, not worker B?
Maybe we can add a field `workerId` to `DriverStateChanged`, but is it possible
the second run of `driverId1` is on worker A? consider the following scenario:
1. worker A network partitioned
2. master put `driverId1` to waitingDrivers
3. worker A reconnects and register
4. master launch `driverId1` on worker A
5. worker A's `WorkerLatestState(_,_,Seq(driverId1))` arrives at master
Now, how does worker A handle the `LaunchDriver(driverId1)` when it has
already running a driver with `driverId1`? how does the master process
`WorkerLatestState`? With the above message order, master will send
`KillDriver` to worker A, then worker will kill `driverId1`, which is the
relaunched one, then send `DriverStateChanged` to master, master will relaunch
it...
After all this, I think it better to relaunch the driver with a new id to
make it simple. As to the cost, `removeDriver` will be called anyway, if not
here, it will be called when `DriverStateChanged` come. `persistenceEngine`
have to be called because the persistent state `driver.id` changed. So the cost
is justified. And `relaunchDriver` is called when worker down or master down,
it seems rarely because framework code is more stable than application code, so
software bugs are less likely.
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