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

[HunDunDM]

This is a 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:

• disksing
• lhy1024

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[HunDunDM]

/rebuild

[codecov]

Codecov Report

Merging #4178 (fe5b3ec) into release-5.1-20210926 (897734a) will increase coverage by 0.04%.
The diff coverage is n/a.

@@                   Coverage Diff                    @@
##           release-5.1-20210926    #4178      +/-   ##
========================================================
+ Coverage                 75.26%   75.30%   +0.04%     
========================================================
  Files                       245      245              
  Lines                     24863    24859       -4     
========================================================
+ Hits                      18713    18720       +7     
+ Misses                     4523     4518       -5     
+ Partials                   1627     1621       -6     

Flag	Coverage Δ
unittests	75.30% <ø> (+0.04%)	⬆️

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	81.00% <ø> (+0.89%)	⬆️
server/region_syncer/server.go	83.33% <0.00%> (-6.07%)	⬇️
server/tso/allocator_manager.go	78.63% <0.00%> (-1.17%)	⬇️
server/cluster/cluster.go	83.25% <0.00%> (-0.81%)	⬇️
server/core/storage.go	67.68% <0.00%> (-0.77%)	⬇️
server/cluster/coordinator.go	73.34% <0.00%> (-0.71%)	⬇️
client/client.go	71.96% <0.00%> (+0.13%)	⬆️
server/grpc_service.go	48.34% <0.00%> (+0.22%)	⬆️
server/member/member.go	68.81% <0.00%> (+0.53%)	⬆️
... and 9 more

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[HunDunDM]

/merge

[ti-chi-bot]

@HunDunDM: 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: fe5b3ec