prepare_snap: establish connection to all stores before pausing admin

[YuJuncen]

What problem does this PR solve?

Issue Number: close #51448

Problem Summary:
Now if we cannot connect to a TiKV, it will block at creating connection.
But, in this scenario, some of TiKVs' admin commands are paused. That will impact the TP workload more.

What changed and how does it work?

After this PR, we won't pause the admin commands before connections to all TiKV nodes established.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[tiprow]

Hi @YuJuncen. Thanks for your PR.

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[codecov]

Codecov Report

Merging #51449 (5129f10) into master (8e7658d) will increase coverage by 1.7011%.
Report is 126 commits behind head on master.
The diff coverage is 62.2222%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #51449        +/-   ##
================================================
+ Coverage   70.6487%   72.3499%   +1.7011%     
================================================
  Files          1462       1475        +13     
  Lines        435031     454834     +19803     
================================================
+ Hits         307344     329072     +21728     
+ Misses       108388     105728      -2660     
- Partials      19299      20034       +735     

Flag	Coverage Δ
integration	47.1167% <0.0000%> (?)
unit	70.4848% <62.2222%> (+0.0456%)	⬆️

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

Components	Coverage Δ
dumpling	53.9957% <ø> (ø)
parser	∅ <ø> (∅)
br	46.6229% <62.2222%> (+0.7779%)	⬆️

[3pointer]

why use two loops? seems it can be done without clients map

[YuJuncen]

The first createAndCacheStream must happens after ALL connections established. I think we cannot remove this. Or would you give a code snippet?

[3pointer]

for _, store := range stores {
	cli, err := p.env.ConnectToStore(ctx, store.Id)
	if err != nil {
		return errors.Annotatef(err, "failed to dial the store %d", store.Id)
	}
    if err := p.createAndCacheStream(ctx, cli, store.Id); err != nil {
		return errors.Annotatef(err, "failed to create and cache stream for store %d", id)
	}	
}

[YuJuncen]

THis will make createAndCacheStream concurrency with ConnectToStore, recall that:

The first createAndCacheStream must happens after ALL connections established.

[3pointer]

...then what's problem with that?

[YuJuncen]

/unit-test

[YuJuncen]

/test unit-test

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[BornChanger]

/retest

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-03-07 05:37:43.507296883 +0000 UTC m=+318290.529543271: ☑️ agreed by 3pointer.
• 2024-03-11 15:23:28.04959112 +0000 UTC m=+699035.071837507: ☑️ agreed by BornChanger.

[BornChanger]

/retest

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[BornChanger]

/retest

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[BornChanger]

/retest

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[BornChanger]

/ok-to-test

[YuJuncen]

/retest-required

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: 3pointer, BornChanger

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[tiprow]

@YuJuncen: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
tidb_parser_test	45358ed	link	true	/test tidb_parser_test

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[BornChanger]

/label needs-cherry-pick-release-6.5

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #51730.

[YuJuncen]

/retest-required

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #52566.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #52567.