scheduler: allow empty region to be scheduled and use a sperate tolerance config in scatter range scheduler (#4106)

[ti-chi-bot]

This is an automated cherry-pick of #4106

What problem does this PR solve?

1. we expect the tolerance ratio in range cluster should be 2, but it doesn't take effect.
   

   pd/server/schedulers/scatter_range.go

   Line 220 in 3f53f1e

   c.SetTolerantSizeRatio(2)

   
   

   pd/server/schedulers/utils.go

   Line 154 in 3f53f1e

   tolerantSizeRatio := cluster.GetOpts().GetTolerantSizeRatio()

2. we expect it can schedule empty region, but it can not and test can not detect
   

   pd/server/core/region.go

   Line 96 in 3f53f1e

   EmptyRegionApproximateSize = 1

   
   

   pd/server/schedulers/balance_test.go

   Lines 1103 to 1111 in 3f53f1e

   	// empty case
   	regions[49].EndKey = []byte("")
   	for _, meta := range regions {
   	leader := rand.Intn(4) % 3
   	regionInfo := core.NewRegionInfo(
   	meta,
   	meta.Peers[leader],
   	core.SetApproximateKeys(96),
   	core.SetApproximateSize(96),

What is changed and how it works?

allow empty region to be scheduled and use a sperate tolerance config in scatter range scheduler

Check List

Tests

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

Add scatter range scheduler

Before this pr

After this pr

Related changes

• Need to cherry-pick to the release branch

Release note

allow empty region to be scheduled and use a sperate tolerance config in scatter range scheduler

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• lhy1024
• rleungx

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[nolouch]

@lhy1024 plz fix the conflict.

[rleungx]

CI failed

[codecov]

Codecov Report

Merging #4116 (f0b312d) into release-5.0 (7161fde) will decrease coverage by 0.16%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           release-5.0    #4116      +/-   ##
===============================================
- Coverage        75.05%   74.88%   -0.17%     
===============================================
  Files              245      245              
  Lines            24370    24382      +12     
===============================================
- Hits             18290    18258      -32     
- Misses            4475     4506      +31     
- Partials          1605     1618      +13     

Flag	Coverage Δ
unittests	74.88% <100.00%> (-0.17%)	⬇️

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

Impacted Files	Coverage Δ
server/schedulers/balance_region.go	87.40% <100.00%> (+0.62%)	⬆️
server/schedulers/utils.go	93.90% <100.00%> (+0.23%)	⬆️
pkg/tempurl/tempurl.go	45.00% <0.00%> (-15.00%)	⬇️
server/member/member.go	63.04% <0.00%> (-8.16%)	⬇️
server/tso/tso.go	68.71% <0.00%> (-6.75%)	⬇️
server/id/id.go	80.95% <0.00%> (-4.77%)	⬇️
server/tso/allocator_manager.go	75.74% <0.00%> (-3.66%)	⬇️
server/election/leadership.go	87.05% <0.00%> (-2.36%)	⬇️
client/base_client.go	82.47% <0.00%> (-2.07%)	⬇️
server/election/lease.go	94.91% <0.00%> (-1.70%)	⬇️
... and 7 more

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[lhy1024]

/merge

[ti-chi-bot]

@lhy1024: 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: a6cf0a2

[ti-chi-bot]

@ti-chi-bot: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

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[lhy1024]

/rebuild

[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

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.