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Review request for Aurora, Stephan Erb and Zameer Manji. Bugs: AURORA-1779 https://issues.apache.org/jira/browse/AURORA-1779 Repository: aurora Description ------- ######Problem The current `BatchWorker` error handling assumes graceful recovery if any of the individual batch items fail. This may not hold true if the storage is modified _before_ the error is thrown and the `LogStorage` transaction is not rolled back. Consider the following fragment from the `StateManagerImpl`: ``` storeProvider.getUnsafeTaskStore().saveTasks(scheduledTasks); for (IScheduledTask scheduledTask : scheduledTasks) { updateTaskAndExternalState( storeProvider.getUnsafeTaskStore(), Tasks.id(scheduledTask), Optional.of(scheduledTask), Optional.of(PENDING), Optional.absent()); } ``` If a task is saved but the subsequent `updateTaskAndExternalState()` throws AND `BatchWorker` catches and logs that exception, the native store transaction will be committed and as a result the storage will be left in a logically inconsistent state. ######Solution I can see at least 3 ways to solve this problem: 1. Fail hard and shutdown scheduler when any of the batch items throw; 2. Fail only the last batch (drop all its items) and let storage transaction roll back; 3. Implement `BatchWorker` transaction where items _before_ and _after_ the failed item would be retried when the storage transaction rolls back; The #3 is the most involved and would be very hard to get right (assuming batch items are idempotent, which may not be the case). The #2 may result in a very hard to troubleshoot scenario where _some_ items would be dropped on the floor and never completed. I suggest we go with #1 as the most straightforward and transparent approach. It's also the only one that ensures storage state consistency, which is the most vital invariant to preserve (as AURORA-1779 proves). The only downside of this approach is that scheduler will go down hard any time an unhandled error is thrown but arguably this is the easiest way to improve our codebase and certainly better than leaving the scheduler in a crippled state. Diffs ----- src/main/java/org/apache/aurora/scheduler/BatchWorker.java e05d4b48749b0691902a505bea1b4490fdd08f29 src/main/java/org/apache/aurora/scheduler/SchedulerModule.java 2ec3967ddb1d470cf681de062a6400f647978185 src/main/java/org/apache/aurora/scheduler/cron/quartz/AuroraCronJob.java 7c8047a7235a937c29fe96517242923ff84a080c src/main/java/org/apache/aurora/scheduler/scheduling/TaskGroups.java d390c07522d22e43d79ce4370985f3643ef021ca src/test/java/org/apache/aurora/scheduler/BatchWorkerTest.java a86dc82cafa7f5436d2b8d00c6db575ff8311eea src/test/java/org/apache/aurora/scheduler/cron/quartz/CronIT.java 8556253fc11f6027316871eb9dc66d8627a77fe6 Diff: https://reviews.apache.org/r/52141/diff/ Testing ------- unit and e2e tests Thanks, Maxim Khutornenko