planner: avoid exceeding the configured concurrency limit (#61786)

[ti-chi-bot]

This is an automated cherry-pick of #61786

What problem does this PR solve?

Issue Number: close #61785

Problem Summary:

The issue is that customers have observed higher I/O consumption when the analyze operation reaches the index, compared to when it analyzes regular tables. (The analyze status contains sensitive information, so it will not be included here.)

The root cause of the issue lies in improper coding practices. When we perform the analyze operation, we create multiple concurrent tasks to execute it. However, within these concurrently spawned goroutines, we further create additional concurrency. This nested concurrency results in an actual level of parallelism that is significantly higher than we anticipated.

CREATE TABLE `test` (
  `c1` binary(16) NOT NULL,
  `c2` tinyint(1) NOT NULL DEFAULT '0',
  `c3` int NOT NULL,
  `c4` varchar(48) COLLATE utf8mb4_general_ci NOT NULL,
  `c5` varchar(512) COLLATE utf8mb4_general_ci DEFAULT NULL,
  `c6` enum('A','B','C') COLLATE utf8mb4_general_ci DEFAULT NULL,
  `c7` int unsigned NOT NULL DEFAULT '0',
  `c8` int unsigned NOT NULL DEFAULT '0',
  `c9` tinyint(1) GENERATED ALWAYS AS (`c7` > 0) VIRTUAL NOT NULL,
  `c10` int DEFAULT NULL,
  `c11` datetime(3) NOT NULL DEFAULT CURRENT_TIMESTAMP(3),
  `c12` datetime(3) NOT NULL DEFAULT CURRENT_TIMESTAMP(3),
  PRIMARY KEY (`c1`) /*T![clustered_index] CLUSTERED */,
  KEY `idx_c4_c2_c9_c3_c12_c5_c6` (`c4`,`c2`,`c9`,`c3`,`c12`,`c5`,`c6`),
  KEY `idx_c4_c2_c9_c12_c5_c6` (`c4`,`c2`,`c9`,`c12`,`c5`,`c6`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;

analyze table chat_session all columns ;

show analyze status

+--------------+------------+----------------+-----------------------------------------------------------------------------------------------------------------+----------------+---------------------+---------------------+----------+-------------+----------------+------------+-------------------+----------+----------------------+
| Table_schema | Table_name | Partition_name | Job_info                                                                                                        | Processed_rows | Start_time          | End_time            | State    | Fail_reason | Instance       | Process_ID | Remaining_seconds | Progress | Estimated_total_rows |
+--------------+------------+----------------+-----------------------------------------------------------------------------------------------------------------+----------------+---------------------+---------------------+----------+-------------+----------------+------------+-------------------+----------+----------------------+
| test         | test       |                | analyze ndv for index idx_c4_c2_c9_c12_c5_c6                                                                    | 0              | 2025-06-18 14:48:05 | 2025-06-18 14:48:05 | finished | <null>      | 127.0.0.1:4000 | <null>     | <null>            | <null>   | <null>               |
| test         | test       |                | analyze ndv for index idx_c4_c2_c9_c3_c12_c5_c6                                                                 | 0              | 2025-06-18 14:48:05 | 2025-06-18 14:48:05 | finished | <null>      | 127.0.0.1:4000 | <null>     | <null>            | <null>   | <null>               |
| test         | test       |                | analyze table all indexes, columns c1, c2, c3, c4, c5, c6, c7, c9, c12 with 256 buckets, 100 topn, 1 samplerate | 0              | 2025-06-18 14:48:05 | 2025-06-18 14:48:05 | finished | <null>      | 127.0.0.1:4000 | <null>     | <null>            | <null>   | <null>               |
+--------------+------------+----------------+-----------------------------------------------------------------------------------------------------------------+----------------+---------------------+---------------------+----------+-------------+----------------+------------+-------------------+----------+----------------------+

You will see that it will create two task about analyze ndv for index.

the problem is here.

The first creation of concurrency

tidb/pkg/executor/analyze.go

Lines 121 to 126 in 8fc1430

	// Start workers with channel to collect results.
	taskCh := make(chan *analyzeTask, buildStatsConcurrency)
	resultsCh := make(chan *statistics.AnalyzeResults, 1)
	for range buildStatsConcurrency {
	e.wg.Run(func() { e.analyzeWorker(taskCh, resultsCh) })
	}

The second creation of concurrency

AnalyzeExec.analyzeWorker -> analyzeColumnsPushDownEntry -> analyzeColumnsPushDownV2

https://github.com/pingcap/tidb/blob/master/pkg/executor/analyze_col_v2.go#L105-L107

The third creation of concurrency

tidb/pkg/executor/analyze_col_v2.go

Lines 461 to 466 in 8fc1430

	var subIndexWorkerWg = NewAnalyzeResultsNotifyWaitGroupWrapper(resultsCh)
	subIndexWorkerWg.Add(statsConcurrncy)
	for range statsConcurrncy {
	subIndexWorkerWg.Run(func() { e.subIndexWorkerForNDV(taskCh, resultsCh) })
	}
	for _, task := range tasks {

This part is actually the most dangerous. It allows the concurrency of handleNDVForSpecialIndexes and the concurrency of column collection to coexist, which increases the business risk.

What changed and how does it work?

1、Wait untilhandleNDVForSpecialIndexesis completed before proceeding with the statistics collection for columns.

2、To prevent modifying the build stats concurrency, which could result in an exponential relationship in the actual number of concurrent tasks, we set the concurrency here to be the same as the build sampling concurrency.

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

[ti-chi-bot]

@hawkingrei This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[fixdb]

fix the conflict

[hawkingrei]

/unhold

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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 [AilinKid,hawkingrei]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-07-04 23:33:38.094147216 +0000 UTC m=+1697070.817326196: ☑️ agreed by hawkingrei.
• 2025-07-08 09:34:30.982899874 +0000 UTC m=+1992323.706078856: ☑️ agreed by AilinKid.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release-7.5@469af9d). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.5     #61813   +/-   ##
================================================
  Coverage               ?   72.2023%           
================================================
  Files                  ?       1417           
  Lines                  ?     414294           
  Branches               ?          0           
================================================
  Hits                   ?     299130           
  Misses                 ?      95172           
  Partials               ?      19992           

Flag	Coverage Δ
unit	72.2023% <100.0000%> (?)

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Components	Coverage Δ
dumpling	52.9400% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	53.5323% <0.0000%> (?)

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[fixdb]

/retest