domain,infoschema: avoid v1/v2 switch when loading snapshot infoschema

[tiancaiamao]

What problem does this PR solve?

Issue Number: close #55114

Problem Summary:

What changed and how does it work?

Compatibility between infoschema snapshot and v1&v2 switch is difficult.
snapshot needs the history, while v1&v2 swtich reset the infoschema history,
this conflict is the root cause of bugs like #55114 #54926

So what I do in this commit is to avoid such case happen together:
If it's a loading of snapshot infoschema, then avoid v1&v2 switch.

Now whether the infoschema builder should build v2 is not decided soly by variable.SchemaCacheSize > 0, it's also affect by whether this loading isSnapshot. Provide a shouldUseV2() function for that.

Check List

Tests

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

I try to add a unit test like this:

func TestIssue55114(t *testing.T) {
	store, dom := testkit.CreateMockStoreAndDomain(t)
	tk := testkit.NewTestKit(t, store)
	tk2 := testkit.NewTestKit(t, store)
	tk.MustExec("use test")
	// For mocktikv, safe point is not initialized, we manually insert it for snapshot to use.
	safePointName := "tikv_gc_safe_point"
	safePointValue := "20160102-15:04:05 -0700"
	safePointComment := "All versions after safe point can be accessed. (DO NOT EDIT)"
	updateSafePoint := fmt.Sprintf(`INSERT INTO mysql.tidb VALUES ('%[1]s', '%[2]s', '%[3]s')
	ON DUPLICATE KEY
	UPDATE variable_value = '%[2]s', comment = '%[3]s'`, safePointName, safePointValue, safePointComment)
	tk.MustExec(updateSafePoint)

	time1 := time.Now()
	// time1TS := oracle.GoTimeToTS(time1)
	schemaVer1 := tk.Session().GetInfoSchema().SchemaMetaVersion()
	time.Sleep(50*time.Millisecond)
	tk.MustExec("create table t (id int)")
	fmt.Println("before .. version ==", schemaVer1)

	go func() {
		for {
			tk.MustExec("set @@global.tidb_schema_cache_size = 0")
			dom.Reload()
			tk.MustExec("set @@global.tidb_schema_cache_size = 512 * 1024 * 1024")
			dom.Reload()
		}
	}()

	go func() {
		for {
			tk2.MustExec(fmt.Sprintf(`set @@tidb_snapshot="%s"`, time1.Format("2006-1-2 15:04:05.000")))
			time.Sleep(10*time.Millisecond)
		}
	}()

	for i:=0; i<1000; i++ {
		time.Sleep(100 * time.Millisecond)
		v := dom.InfoSchema().SchemaMetaVersion()
		fmt.Println("v ===", v)
		require.NotEqual(t, v, schemaVer1)
	}
}

The test works well and prove the correctness of this change.
But it's not feasible to be added to unit test, because how long it runs is undetermined.

• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

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

None

[tiprow]

Hi @tiancaiamao. Thanks for your PR.

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[codecov]

Codecov Report

Attention: Patch coverage is 73.33333% with 8 lines in your changes missing coverage. Please review.

Project coverage is 74.3777%. Comparing base (52303d4) to head (b255561).
Report is 1 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #55129        +/-   ##
================================================
+ Coverage   72.9177%   74.3777%   +1.4599%     
================================================
  Files          1568       1568                
  Lines        439181     439192        +11     
================================================
+ Hits         320241     326661      +6420     
+ Misses        99308      92133      -7175     
- Partials      19632      20398       +766     

Flag	Coverage Δ
integration	20.6282% <73.3333%> (?)

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

Components	Coverage Δ
dumpling	52.9567% <ø> (ø)
parser	∅ <ø> (∅)
br	61.0830% <ø> (+15.1897%)	⬆️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lance6716, wjhuang2016

The full list of commands accepted by this bot can be found here.

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Needs approval from an approver in each of these files:

• OWNERS [lance6716,wjhuang2016]
• pkg/ddl/OWNERS [wjhuang2016]
• pkg/domain/OWNERS [lance6716,wjhuang2016]
• pkg/infoschema/OWNERS [wjhuang2016]

Approvers can indicate their approval by writing /approve in a comment
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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-08-01 08:58:04.474545499 +0000 UTC m=+432600.754593568: ☑️ agreed by wjhuang2016.
• 2024-08-01 09:07:43.729541389 +0000 UTC m=+433180.009589458: ☑️ agreed by lance6716.

[tiancaiamao]

/retest

[tiprow]

@tiancaiamao: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/retest

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 kubernetes-sigs/prow repository.

[tiancaiamao]

/ok-to-test

[lance6716]

/retest

[lance6716]

/check-issue-triage-complete

[hawkingrei]

/retest

[tiancaiamao]

/retest