planner: fix no access path when TiKV read is disabled under RC isolation

[hawkingrei]

What problem does this PR solve?

Issue Number: close #65059

Problem Summary:

What changed and how does it work?

Because we use RC isolation, so isForUpdateRead is true.

tidb/pkg/planner/core/planbuilder.go

Lines 467 to 469 in 6540abd

	b.hintProcessor = processor
	b.isForUpdateRead = sctx.GetSessionVars().IsPessimisticReadConsistency()
	b.noDecorrelate = sctx.GetSessionVars().EnableNoDecorrelateInSelect

Here will not remove the tikv path.

tidb/pkg/planner/core/logical_plan_builder.go

Lines 4491 to 4501 in 6540abd

	// remain tikv access path to generate point get acceess path if existed
	// see detail in issue: https://github.com/pingcap/tidb/issues/39543
	if !(b.isForUpdateRead && b.ctx.GetSessionVars().TxnCtx.IsExplicit) {
	// Skip storage engine check for CreateView.
	if b.capFlag&canExpandAST == 0 {
	possiblePaths, err = util.FilterPathByIsolationRead(b.ctx, possiblePaths, tblName, dbName)
	if err != nil {
	return nil, err
	}
	}
	}

findBestTask4LogicalDataSource will remove the tiflash path when isForUpdateRead is true

tidb/pkg/planner/core/find_best_task.go

Lines 1644 to 1667 in 6540abd

	if ds.IsForUpdateRead && ds.SCtx().GetSessionVars().TxnCtx.IsExplicit {
	hasPointGetPath := false
	for _, path := range ds.PossibleAccessPaths {
	if isPointGetPath(ds, path) {
	hasPointGetPath = true
	break
	}
	}
	tblName := ds.TableInfo.Name
	ds.PossibleAccessPaths, err = util.FilterPathByIsolationRead(ds.SCtx(), ds.PossibleAccessPaths, tblName, ds.DBName)
	if err != nil {
	return nil, err
	}
	if hasPointGetPath {
	newPaths := make([]*util.AccessPath, 0)
	for _, path := range ds.PossibleAccessPaths {
	// if the path is the point get range path with for update lock, we should forbid tiflash as it's store path (#39543)
	if path.StoreType != kv.TiFlash {
	newPaths = append(newPaths, path)
	}
	}
	ds.PossibleAccessPaths = newPaths
	}
	}

If this expression is not of the type "select for update" and there are no tikv replicas, even if it is set to RC, it will not cut off tiflash. However, if it is of the type "select for update," then tiflash will be cut off and it will be forced to use tikv.

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.

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

[codecov]

Codecov Report

❌ Patch coverage is 44.44444% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.5957%. Comparing base (8227b49) to head (31c7b06).
⚠️ Report is 13 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #65127        +/-   ##
================================================
- Coverage   70.7556%   68.5957%   -2.1599%     
================================================
  Files          1895       1873        -22     
  Lines        517902     510371      -7531     
================================================
- Hits         366445     350093     -16352     
- Misses       126934     137898     +10964     
+ Partials      24523      22380      -2143     

Flag	Coverage Δ
integration	41.5517% <44.4444%> (-6.6188%)	⬇️

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

Components	Coverage Δ
dumpling	52.8700% <ø> (ø)
parser	∅ <ø> (∅)
br	38.4708% <ø> (-19.7658%)	⬇️

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[hawkingrei]

/retest

[hawkingrei]

/retest

[hawkingrei]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: you06
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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-12-19 10:31:38.262126942 +0000 UTC m=+1814643.075904504: ☑️ agreed by you06.

[tiprow]

@hawkingrei: 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
fast_test_tiprow	31c7b06	link	true	/test fast_test_tiprow

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[ti-chi-bot]

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

Test name	Commit	Details	Required	Rerun command
pull-unit-test-next-gen	31c7b06	link	true	/test pull-unit-test-next-gen
idc-jenkins-ci-tidb/unit-test	31c7b06	link	true	/test unit-test

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