planner: fix get wrong cost with cost tracer

[hawkingrei]

What problem does this PR solve?

Issue Number: close #61155

Problem Summary:

When we use the cost trace's explain, it will calculate the cost twice. Unfortunately, when calculating secondly, the row count has been polluted by the first.

the first calculation:

1500000000*math.log2(46.17)*11.6+10000*math.log2(46.17)*11.6 = 96203219945.10272

1500000000 will become the 5.645217633333338e+07, because postOptimize‘s
tryEnableLateMaterialization can change the row count in the first plan generate.

tidb/pkg/planner/core/tiflash_selection_late_materialization.go

Lines 283 to 290 in 7419112

	func PushedDown(sel *PhysicalSelection, ts *PhysicalTableScan, selectedConds []expression.Expression, selectedSelectivity float64) {
	// remove the pushed down conditions from selection
	removeSpecificExprsFromSelection(sel, selectedConds)
	// add the pushed down conditions to table scan
	ts.LateMaterializationFilterCondition = selectedConds
	// Update the row count of table scan after pushing down the conditions.
	ts.StatsInfo().RowCount *= selectedSelectivity
	}

the second calculation:

5.645217633333338e+07*math.log2(46.17)*11.6+10000*math.log2(46.17)*11.6 = 3621204637.5523133

So two formats have different costs.

What changed and how does it work?

Generate the cost trace in the first calculation. Remove the second calculation.

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.

planner: fix get wrong cost with cost tracer

修复使用 cost tracer 得到不正确的 cost 值

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.4846%. Comparing base (9cc4672) to head (a64b07d).
Report is 175 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #61196        +/-   ##
================================================
+ Coverage   73.1823%   73.4846%   +0.3022%     
================================================
  Files          1724       1725         +1     
  Lines        477675     479888      +2213     
================================================
+ Hits         349574     352644      +3070     
+ Misses       106688     105835       -853     
+ Partials      21413      21409         -4     

Flag	Coverage Δ
integration	42.6373% <100.0000%> (?)
unit	72.4701% <100.0000%> (+0.1011%)	⬆️

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Components	Coverage Δ
dumpling	52.7804% <ø> (ø)
parser	∅ <ø> (∅)
br	46.0916% <ø> (-1.6633%)	⬇️

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[Copilot]

Pull Request Overview

This PR fixes an issue where EXPLAIN FORMAT='cost_trace' would calculate plan cost twice (with a polluted row count on the second pass). It enables the optimize-tracing flag only during the initial build and removes the redundant recalculation, then adds a test helper to verify cost consistency.

• Enable StmtCtx.EnableOptimizeTrace only when Format=cost_trace in buildExplain
• Remove the second getPlanCost invocation in RenderResult
• Add checkCost in TestQ1 to compare cost_trace vs verbose outputs and update test dependencies

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
pkg/planner/core/planbuilder.go	Wrap EnableOptimizeTrace in a conditional and defer restore for cost_trace
pkg/planner/core/common_plans.go	Remove the extra getPlanCost call for cost_trace
pkg/planner/core/casetest/tpch/tpch_test.go	Introduce checkCost helper, update TestQ1 to assert cost consistency
pkg/planner/core/casetest/tpch/BUILD.bazel	Add @com_github_stretchr_testify//require to test dependencies

Comments suppressed due to low confidence (3)

pkg/planner/core/planbuilder.go:5553

• [nitpick] The variable name origin is ambiguous; consider renaming it to oldEnableOptimizeTrace or similar to clarify its purpose.

origin := sctx.GetSessionVars().StmtCtx.EnableOptimizeTrace

pkg/planner/core/common_plans.go:1024

• After removing the redundant cost-recalculation block, review and clean up any now-unused imports (e.g., optimizetrace, costusage) to keep the file tidy.

switch strings.ToLower(e.Format) {

pkg/planner/core/casetest/tpch/tpch_test.go:223

• Consider adding a checkCost(t, tk, q4) call after this MPP-mode query to ensure cost_trace and verbose outputs remain consistent when tidb_enforce_mpp is enabled.

tk.MustQuery(briefFormat + q4).Check(testkit.Rows("Sort 1.00 root  olap.orders.o_orderpriority",

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: AilinKid, qw4990

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• pkg/planner/OWNERS [AilinKid,qw4990]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-05-20 03:20:58.661051043 +0000 UTC m=+59095.762218264: ☑️ agreed by qw4990.
• 2025-05-20 05:27:01.533876501 +0000 UTC m=+66658.635043708: ☑️ agreed by AilinKid.

[hawkingrei]

/cherrypick release-8.5
/cherrypick release-8.1
/cherrypick release-7.5

[ti-chi-bot]

@hawkingrei: new pull request created to branch release-7.5: #61214.
But this PR has conflicts, please resolve them!

In response to this:

/cherrypick release-8.5
/cherrypick release-8.1
/cherrypick release-7.5

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[ti-chi-bot]

@hawkingrei: new pull request created to branch release-8.1: #61216.
But this PR has conflicts, please resolve them!

In response to this:

/cherrypick release-8.5
/cherrypick release-8.1
/cherrypick release-7.5

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[ti-chi-bot]

@hawkingrei: new pull request created to branch release-8.5: #61218.
But this PR has conflicts, please resolve them!

In response to this:

/cherrypick release-8.5
/cherrypick release-8.1
/cherrypick release-7.5

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[hawkingrei]

/cherrypick release-8.1
/cherrypick release-7.5

[ti-chi-bot]

@hawkingrei: new pull request could not be created: failed to create pull request against pingcap/tidb#release-7.5 from head ti-chi-bot:cherry-pick-61196-to-release-7.5: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for ti-chi-bot:cherry-pick-61196-to-release-7.5."}],"documentation_url":"https://docs.github.com/rest/pulls/pulls#create-a-pull-request","status":"422"}

In response to this:

/cherrypick release-8.1
/cherrypick release-7.5

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.

[ti-chi-bot]

@hawkingrei: new pull request could not be created: failed to create pull request against pingcap/tidb#release-8.1 from head ti-chi-bot:cherry-pick-61196-to-release-8.1: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for ti-chi-bot:cherry-pick-61196-to-release-8.1."}],"documentation_url":"https://docs.github.com/rest/pulls/pulls#create-a-pull-request","status":"422"}

In response to this:

/cherrypick release-8.1
/cherrypick release-7.5

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.

[hawkingrei]

/cherrypick release-7.5

[ti-chi-bot]

In response to a cherrypick label: new pull request could not be created: failed to create pull request against pingcap/tidb#release-8.1 from head ti-chi-bot:cherry-pick-61196-to-release-8.1: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for ti-chi-bot:cherry-pick-61196-to-release-8.1."}],"documentation_url":"https://docs.github.com/rest/pulls/pulls#create-a-pull-request","status":"422"}

[ti-chi-bot]

In response to a cherrypick label: new pull request could not be created: failed to create pull request against pingcap/tidb#release-7.5 from head ti-chi-bot:cherry-pick-61196-to-release-7.5: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for ti-chi-bot:cherry-pick-61196-to-release-7.5."}],"documentation_url":"https://docs.github.com/rest/pulls/pulls#create-a-pull-request","status":"422"}

[ti-chi-bot]

@hawkingrei: new pull request could not be created: failed to create pull request against pingcap/tidb#release-7.5 from head ti-chi-bot:cherry-pick-61196-to-release-7.5: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for ti-chi-bot:cherry-pick-61196-to-release-7.5."}],"documentation_url":"https://docs.github.com/rest/pulls/pulls#create-a-pull-request","status":"422"}

In response to this:

/cherrypick release-7.5

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.