handle: use separete ctx for initStats

[Yisaer]

What problem does this PR solve?

Issue Number: close #40548

Problem Summary:

What is changed and how it works?

use separete ctx for initStats in order to avoid initStats blocking server starting process

Check List

Tests

• Manual test (add detailed scripts or steps below)

we manually insert Sleep in initStats and start client session to tidb-server. Before this pr, the client session would be blocked, after this pr, the client session can be prcessed successfully.

// InitStats will init the stats cache using full load strategy.
func (h *Handle) InitStats(is infoschema.InfoSchema) (err error) {
	loadFMSketch := config.GetGlobalConfig().Performance.EnableLoadFMSketch
	ctx := kv.WithInternalSourceType(context.Background(), kv.InternalTxnStats)
	defer func() {
		_, err1 := h.initStatsCtx.(sqlexec.SQLExecutor).ExecuteInternal(ctx, "commit")
		if err == nil && err1 != nil {
			err = err1
		}
	}()
	time.Sleep(2 * time.Minute)
	_, err = h.initStatsCtx.(sqlexec.SQLExecutor).ExecuteInternal(ctx, "begin")
	if err != nil {
		return err
	}
        ......
}

Release note

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None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• hawkingrei
• xuyifangreeneyes

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[xuyifangreeneyes]

I think that rateMap can have its own mutex, too. Maybe we can do that in the PR or in another PR, either is ok for me.

[Yisaer]

we will change it later

[Yisaer]

/retest-required

[Yisaer]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: b9859c7

[Yisaer]

/retest-required

[hawkingrei]

/run-mysql-test

[hawkingrei]

/run-mysql-test

[Yisaer]

/retest-required

[ti-chi-bot]

@Yisaer: Your PR was out of date, I have automatically updated it for you.

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #40623.