cluster: avoid unexpected statistic modify in range cluster (#3599)

[ti-srebot]

cherry-pick #3599 to release-5.0
You can switch your code base to this Pull Request by using git-extras:

# In pd repo:
git pr https://github.com/tikv/pd/pull/3602

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

git push git@github.com:ti-srebot/pd.git pr/3602:release-5.0-9097e68c4db5

---

Signed-off-by: lhy1024 admin@liudos.us

What problem does this PR solve?

After add the scatter range scheduler, will cause the #3598, the disk used space drop to 0. this PR try to fix a part of that.

What is changed and how it works?

#3598 are caused with two problems, this pr fix one, another is #3597

Check List

Tests

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

Release note

• Avoid unexpected statistic modify after adding scatter region scheduler

[ti-srebot]

@lhy1024 you're already a collaborator in bot's repo.

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• disksing
• lhy1024

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[disksing]

/merge

[ti-chi-bot]

@disksing: 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: afd34de

[lhy1024]

/rebuild

[codecov]

Codecov Report

Merging #3602 (afd34de) into release-5.0 (be06738) will decrease coverage by 0.01%.
The diff coverage is 80.00%.

@@               Coverage Diff               @@
##           release-5.0    #3602      +/-   ##
===============================================
- Coverage        74.65%   74.63%   -0.02%     
===============================================
  Files              245      245              
  Lines            24085    24094       +9     
===============================================
+ Hits             17980    17982       +2     
- Misses            4497     4500       +3     
- Partials          1608     1612       +4     

Flag	Coverage Δ
unittests	74.63% <80.00%> (-0.02%)	⬇️

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

Impacted Files	Coverage Δ
server/core/store_stats.go	77.77% <66.66%> (-1.17%)	⬇️
server/core/store_option.go	100.00% <100.00%> (ø)
server/schedule/range_cluster.go	87.03% <100.00%> (ø)
server/schedule/operator/step.go	67.44% <0.00%> (-1.67%)	⬇️
server/election/leadership.go	85.88% <0.00%> (-1.18%)	⬇️
server/core/storage.go	67.68% <0.00%> (-0.77%)	⬇️
server/server.go	72.29% <0.00%> (-0.61%)	⬇️
server/cluster/cluster.go	83.29% <0.00%> (-0.49%)	⬇️
pkg/tempurl/tempurl.go	60.00% <0.00%> (ø)
server/grpc_service.go	47.62% <0.00%> (ø)
... and 4 more

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