range: wrongly skip the candidate in the extractBestCNFItemRanges (#62585)

[ti-chi-bot]

This is an automated cherry-pick of #62585

What problem does this PR solve?

Issue Number: close #62547

Problem Summary:

What changed and how does it work?

tidb/pkg/util/ranger/detacher.go

Lines 313 to 353 in cbab9b2

	func extractBestCNFItemRanges(sctx *rangerctx.RangerContext, conds []expression.Expression, cols []*expression.Column,
	lengths []int, rangeMaxSize int64, convertToSortKey bool) (*cnfItemRangeResult, []*valueInfo, error) {
	if len(conds) < 2 {
	return nil, nil, nil
	}
	var bestRes *cnfItemRangeResult
	columnValues := make([]*valueInfo, len(cols))
	for i, cond := range conds {
	tmpConds := []expression.Expression{cond}
	colSets := expression.ExtractColumnSet(cond)
	if colSets.Len() == 0 {
	continue
	}
	// When we build ranges for the CNF item, we choose not to merge consecutive ranges because we hope to get point
	// ranges here. See https://github.com/pingcap/tidb/issues/41572 for more details.
	//
	// Here is an example. Assume that the index is `idx(a,b,c)` and the condition is `((a,b) in ((1,1),(1,2)) and c = 1`.
	// We build ranges for `(a,b) in ((1,1),(1,2))` and get `[1 1, 1 1] [1 2, 1 2]`, which are point ranges and we can
	// append `c = 1` to the point ranges. However, if we choose to merge consecutive ranges here, we get `[1 1, 1 2]`,
	// which are not point ranges, and we cannot append `c = 1` anymore.
	res, err := detachCondAndBuildRange(sctx, tmpConds, cols, lengths, rangeMaxSize, convertToSortKey, false)
	if err != nil {
	return nil, nil, err
	}
	if len(res.Ranges) == 0 {
	return &cnfItemRangeResult{rangeResult: res, offset: i}, nil, nil
	}
	// take the union of the two columnValues
	columnValues = unionColumnValues(columnValues, res.ColumnValues)
	if len(res.AccessConds) == 0 || len(res.RemainedConds) > 0 {
	continue
	}
	curRes := getCNFItemRangeResult(sctx, res, i)
	bestRes = mergeTwoCNFRanges(sctx, cond, bestRes, curRes)
	}
	if bestRes != nil && bestRes.rangeResult != nil {
	bestRes.rangeResult.IsDNFCond = false
	}
	return bestRes, columnValues, nil
	}

The implementation here has an issue. If a remaining condition is found in extractBestCNFItemRanges, it will not be considered in the final range, which is incorrect.

for example

create table t2 (a varchar(10), b varchar(10), c varchar(10), d varchar(10), index idx(a(2), b(2), c(2)));

select * from t2 where (a, b) in (('aaa', 'bbb'), ('ccc', 'ddd')) and c = 'eee';

Because his index is a very restrictive condition, selection filtering is needed to make good use of this index. At this time, this range must be retained instead of being excluded just because it also contains remaining conditions.

before this PR

+---------------------------+---------+-----------+------------------------------+----------------------------------------------------------------------------------------------------------------------------+
| id                        | estRows | task      | access object                | operator info                                                                                                              |
+---------------------------+---------+-----------+------------------------------+----------------------------------------------------------------------------------------------------------------------------+
| IndexLookUp_12            | 1.00    | root      |                              |                                                                                                                            |
| ├─IndexRangeScan_9(Build) | 20.00   | cop[tikv] | table:t2, index:idx(a, b, c) | range:["aa","aa"], ["cc","cc"], keep order:false, stats:pseudo                                                             |
| └─Selection_11(Probe)     | 1.00    | cop[tikv] |                              | eq(test.t2.c, "eee"), or(and(eq(test.t2.a, "aaa"), eq(test.t2.b, "bbb")), and(eq(test.t2.a, "ccc"), eq(test.t2.b, "ddd"))) |
|   └─TableRowIDScan_10     | 20.00   | cop[tikv] | table:t2                     | keep order:false, stats:pseudo                                                                                             |
+---------------------------+---------+-----------+------------------------------+----------------------------------------------------------------------------------------------------------------------------+

after this pr

+---------------------------+---------+-----------+------------------------------+----------------------------------------------------------------------------------------------------------------------------+
| id                        | estRows | task      | access object                | operator info                                                                                                              |
+---------------------------+---------+-----------+------------------------------+----------------------------------------------------------------------------------------------------------------------------+
| IndexLookUp_12            | 1.00    | root      |                              |                                                                                                                            |
| ├─IndexRangeScan_9(Build) | 1.25    | cop[tikv] | table:t2, index:idx(a, b, c) | range:["aa" "bb" "ee","aa" "bb" "ee"], ["cc" "dd" "ee","cc" "dd" "ee"], keep order:false, stats:pseudo                     |
| └─Selection_11(Probe)     | 1.00    | cop[tikv] |                              | eq(test.t2.c, "eee"), or(and(eq(test.t2.a, "aaa"), eq(test.t2.b, "bbb")), and(eq(test.t2.a, "ccc"), eq(test.t2.b, "ddd"))) |
|   └─TableRowIDScan_10     | 1.25    | cop[tikv] | table:t2                     | keep order:false, stats:pseudo                                                                                             |
+---------------------------+---------+-----------+------------------------------+----------------------------------------------------------------------------------------------------------------------------+

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

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[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.

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
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