checker: judging that the peer is down is no longer based on DownSeconds (#4078)

[ti-chi-bot]

This is an automated cherry-pick of #4078

Signed-off-by: HunDunDM hundundm@gmail.com

What problem does this PR solve?

Fix #4077

After #3462, DownSeconds no longer update with the heartbeat. It will cause the down-peer to not be repaired in time.

What is changed and how it works?

Judging that the peer is down is no longer based on DownSeconds.

Check List

Tests

• Unit test

Code changes

Side effects

• Breaking backward compatibility
  • PD judge that the peer is down is no longer based on DownSeconds. In extreme cases, down-peers that would not have been processed will be fixed.

Related changes

• Need to cherry-pick to the release branch

Release note

Fix the bug that PD would not fix down-peer in time.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• HunDunDM
• disksing

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[nolouch]

/merge

[ti-chi-bot]

@nolouch: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

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

Commit hash: 918a5ce

[codecov]

Codecov Report

Merging #4084 (e2848fa) into release-5.2 (bb4b5c7) will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           release-5.2    #4084      +/-   ##
===============================================
+ Coverage        74.68%   74.79%   +0.10%     
===============================================
  Files              249      249              
  Lines            25537    25537              
===============================================
+ Hits             19073    19101      +28     
+ Misses            4778     4759      -19     
+ Partials          1686     1677       -9     

Flag	Coverage Δ
unittests	74.79% <100.00%> (+0.10%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
server/schedule/checker/replica_checker.go	71.11% <ø> (+1.03%)	⬆️
server/schedule/checker/rule_checker.go	81.11% <ø> (+0.89%)	⬆️
server/cluster/cluster.go	83.41% <100.00%> (+0.71%)	⬆️
server/cluster/coordinator.go	73.15% <100.00%> (+0.24%)	⬆️
server/tso/tso.go	61.32% <0.00%> (-3.87%)	⬇️
server/schedulers/random_merge.go	60.00% <0.00%> (-3.34%)	⬇️
server/schedule/operator/step.go	68.10% <0.00%> (-1.67%)	⬇️
server/tso/allocator_manager.go	67.11% <0.00%> (-0.51%)	⬇️
server/grpc_service.go	47.23% <0.00%> (-0.23%)	⬇️
server/schedule/placement/rule_manager.go	83.73% <0.00%> (+0.60%)	⬆️
... and 8 more

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