worker: delete taskState when task is stopped/finished (#1606)

[ti-srebot]

cherry-pick #1606 to release-2.0
You can switch your code base to this Pull Request by using git-extras:

# In dm repo:
git pr https://github.com/pingcap/dm/pull/1614

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/dm.git pr/1614:release-2.0-a557c8b78047

---

What problem does this PR solve?

fix #1594

What is changed and how it works?

delete taskState when task is stopped/finished

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

When task is running:

dm_worker_cpu_usage 3.528409857613362
# HELP dm_worker_task_state state of task, 0 - invalidStage, 1 - New, 2 - Running, 3 - Paused, 4 - Stopped, 5 - Finished
# TYPE dm_worker_task_state gauge
dm_worker_task_state{source_id="mysql-replica-01",task="testdm"} 2
# HELP go_gc_duration_seconds A summary of the pause duration of garbage collection cycles.
# TYPE go_gc_duration_seconds summary

After task is stopped:

# HELP dm_worker_cpu_usage the cpu usage of worker
# TYPE dm_worker_cpu_usage gauge
dm_worker_cpu_usage 3.521312888533776
# HELP go_gc_duration_seconds A summary of the pause duration of garbage collection cycles.
# TYPE go_gc_duration_seconds summary
go_gc_duration_seconds{quantile="0"} 2.6124e-05
go_gc_duration_seconds{quantile="0.25"} 3.0232e-05

Related changes

• Need to cherry-pick to the release branch

[lance6716]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• lance6716

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[lance6716]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 8368a7b