[FLINK-24005] Resource requirements declaration may be incorrect if JobMaster disconnects with a TaskManager with available slots in the SlotPool

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 1.14.0, 1.13.2
• Fix Version/s: 1.14.0, 1.13.3
• Component/s: Runtime / Coordination
• Labels: pull-request-available
• Assignee: Chesnay Schepler
• Reporter: Zhu Zhu
• Created: 26/Aug/21 12:47
• Updated: 02/Sep/21 15:25
• Resolved: 02/Sep/21 15:25

Description

When a TaskManager disconnects with JobMaster, it will trigger the `DeclarativeSlotPoolService#decreaseResourceRequirementsBy()` for all the slots that are registered to the JobMaster from the TaskManager. If the slots are still available, i.e. not assigned to any task, the `decreaseResourceRequirementsBy` may lead to incorrect resource requirements declaration.

For example, there is one job with 3 source tasks only. It requires 3 slots and declares for 3 slots. Initially all the tasks are running. Suddenly one task failed and waits for some delay before restarting. The previous slot is returned to the SlotPool. Now the job requires 2 slots and declares for 2 slots. At this moment, the TaskManager of that returned slot get lost. After the triggered `decreaseResourceRequirementsBy`, the job only declares for 1 slot. Finally, when the failed task starts to re-schedule, the job will declare for 2 slots while it actually needs 3 slots.

The attached log of a real job and logs of the added test in https://github.com/zhuzhurk/flink/commit/59ca0ac5fa9c77b97c6e8a43dcc53ca8a0ad6c37 can demonstrate this case.
Note that the real job is configured with a large "restart-strategy.fixed-delay.delay" and and large "slot.idle.timeout". So possibly in production it is a rare case.

Issue Links

• links to: GitHub Pull Request #17059