8000 TTL scan task will leak when down scaling the scan workers if it failed to cancel the task. · Issue #57708 · pingcap/tidb · GitHub
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TTL scan task will leak when down scaling the scan workers if it failed to cancel the task. #57708

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YangKeao opened this issue Nov 26, 2024 · 0 comments · Fixed by #57718
Closed

TTL scan task will leak when down scaling the scan workers if it failed to cancel the task. #57708

YangKeao opened this issue Nov 26, 2024 · 0 comments · Fixed by #57718
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affects-7.1 This bug affects the 7.1.x(LTS) versions. affects-7.5 This bug affects the 7.5.x(LTS) versions. affects-8.1 This bug affects the 8.1.x(LTS) versions. affects-8.5 This bug affects the 8.5.x(LTS) versions. impact/leak severity/moderate sig/sql-infra SIG: SQL Infra type/bug The issue is confirmed as a bug.

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@YangKeao
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Please answer these questions before submitting your issue. Thanks!

If the scan worker failed to cancel the task, the task.result will always be nil, and it'll never be regarded as finished. See the following function:

func (m *taskManager) resizeScanWorkers(count int) error {
	var err error
	var canceledWorkers []worker
	m.scanWorkers, canceledWorkers, err = m.resizeWorkers(m.scanWorkers, count, func() worker {
		return newScanWorker(m.delCh, m.notifyStateCh, m.sessPool)
	})
	for _, w := range canceledWorkers {
		...

		result := s.PollTaskResult()
		if result != nil {
			jobID = result.task.JobID
			scanID = result.task.ScanID

			scanErr = result.err
		} else {
			// if the scan worker failed to poll the task, it's possible that the `WaitStopped` has timeout
			// we still consider the scan task as finished
			curTask := s.CurrentTask()
			if curTask == nil {
				continue
			}
			jobID = curTask.JobID
			scanID = curTask.ScanID
			scanErr = errors.New("timeout to cancel scan task")
		}

...

		task.result = result
	}
	return err
}

It's easy to fix. We need to assign a result to the scan task.
@YangKeao YangKeao added type/bug The issue is confirmed as a bug. sig/sql-infra SIG: SQL Infra severity/moderate affects-7.1 This bug affects the 7.1.x(LTS) versions. affects-7.5 This bug affects the 7.5.x(LTS) versions. affects-8.1 This bug affects the 8.1.x(LTS) versions. affects-8.5 This bug affects the 8.5.x(LTS) versions. labels Nov 26, 2024
This was referenced Nov 26, 2024
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@ti-chi-bot ti-chi-bot bot closed this as completed in 0215550 Nov 28, 2024
@ti-chi-bot ti-chi-bot mentioned this issue Nov 29, 2024
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ti-chi-bot bot pushed a commit that referenced this issue Jan 7, 2025
@ti-chi-bot
ttl: set a result for timeout scan task during shrinking scan worker (#…
b454755 
…57718) (#57828)

close #57708
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affects-7.1 This bug affects the 7.1.x(LTS) versions. affects-7.5 This bug affects the 7.5.x(LTS) versions. affects-8.1 This bug affects the 8.1.x(LTS) versions. affects-8.5 This bug affects the 8.5.x(LTS) versions. impact/leak severity/moderate sig/sql-infra SIG: SQL Infra type/bug The issue is confirmed as a bug.
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ttl: set a result for timeout scan task during shrinking scan worker YangKeao/tidb
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