refactor(engine): prevent instant rescheduling #9237
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saig0
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Apr 29, 2022
engine/src/main/java/io/camunda/zeebe/engine/processing/scheduled/DueDateChecker.java
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Before this change, the delay calculated to reschedule a task could be negative or close to 0. This lead to the checker being immediately rescheduled. This is bad, because it does not leave room for other tasks to run. With this change, a lower floor is applied when the task is rescheduled.
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9249: Yield control if too many timers due r=pihme a=pihme ## Description Adds a mechanism for the `DueDateTimeChecker` to yield control after some time. This is to stop it from iterating over an unknown number of due timer events and blocking execution while doing so. Overall, this change should work well in cases where there is a huge backlog of timers. This backlog would then be reduced bit by bit. The change is potentially bad for cases in which there is a constant and high load with many timers being created all the time. In this case, the change of this PR can lead to due timers continuously growing and the timers triggered will fall more and more behind real time. Overall, this tradeoff was deemed advantageous. At least it removes that dangers that the iteration blocks the execution for so long that the node is marked as unhealthy. When this situation is reached there is currently no practical recovery possible. Even before this point is reached, execution will be blocked for long stretches of time, and no progress can be made on that partition. So one faulty process can block all others from executing. Both issues are addressed by this PR. With this PR it should be always possible to make some progress, albeit small. This would allow users to cancel or change any faulty process, or to reduce the load if needed. Further work will be needed to figure out a way how to trigger timers without potentially falling further and further behind real time. ## Review Hints This PR has duplicate commits from #9237 ## Related issues <!-- Which issues are closed by this PR or are related --> closes #9238 Co-authored-by: pihme <pihme@users.noreply.github.com>
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Description
Before this change, the delay calculated to reschedule a task could be negative or close to 0.
This lead to the checker being immediately rescheduled. This is bad, because it does not leave room
for other tasks to run.
With this change, a lower floor is applied when the task is rescheduled.
Related issues
closes #9236
preparation for #9238
Definition of Done
Code changes:
backport stable/1.3) to the PR, in case that fails you need to create backports manually.Testing:
Documentation:
Please refer to our review guidelines.