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planner: backport partial order TopN optimization #68995

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12 changes: 6 additions & 6 deletions DEPS.bzl
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -5971,13 +5971,13 @@ def go_deps():
name = "com_github_pingcap_tipb",
build_file_proto_mode = "disable_global",
importpath = "github.com/pingcap/tipb",
sha256 = "af0d5b3d3d28d8c7e43b446873541c0f53a1c552e78fd2eda33931302c9f62e3",
strip_prefix = "github.com/pingcap/tipb@v0.0.0-20260507102040-d3d6e146648f",
sha256 = "8fc936a7308e69dd6a95e5594576ccf3f6229bcb9ef90804c52fb065bb09b403",
strip_prefix = "github.com/pingcap/tipb@v0.0.0-20260605083900-f9f651ef5fbc",
urls = [
"http://bazel-cache.pingcap.net:8080/gomod/github.com/pingcap/tipb/com_github_pingcap_tipb-v0.0.0-20260507102040-d3d6e146648f.zip",
"http://ats.apps.svc/gomod/github.com/pingcap/tipb/com_github_pingcap_tipb-v0.0.0-20260507102040-d3d6e146648f.zip",
"https://cache.hawkingrei.com/gomod/github.com/pingcap/tipb/com_github_pingcap_tipb-v0.0.0-20260507102040-d3d6e146648f.zip",
"https://storage.googleapis.com/pingcapmirror/gomod/github.com/pingcap/tipb/com_github_pingcap_tipb-v0.0.0-20260507102040-d3d6e146648f.zip",
"http://bazel-cache.pingcap.net:8080/gomod/github.com/pingcap/tipb/com_github_pingcap_tipb-v0.0.0-20260605083900-f9f651ef5fbc.zip",
"http://ats.apps.svc/gomod/github.com/pingcap/tipb/com_github_pingcap_tipb-v0.0.0-20260605083900-f9f651ef5fbc.zip",
"https://cache.hawkingrei.com/gomod/github.com/pingcap/tipb/com_github_pingcap_tipb-v0.0.0-20260605083900-f9f651ef5fbc.zip",
"https://storage.googleapis.com/pingcapmirror/gomod/github.com/pingcap/tipb/com_github_pingcap_tipb-v0.0.0-20260605083900-f9f651ef5fbc.zip",
],
)
go_repository(
Expand Down
2 changes: 1 addition & 1 deletion go.mod
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Original file line number Diff line number Diff line change
Expand Up @@ -100,7 +100,7 @@ require (
github.com/pingcap/log v1.1.1-0.20250917021125-19901e015dc9
github.com/pingcap/sysutil v1.0.1-0.20240311050922-ae81ee01f3a5
github.com/pingcap/tidb/pkg/parser v0.0.0-20211011031125-9b13dc409c5e
github.com/pingcap/tipb v0.0.0-20260507102040-d3d6e146648f
github.com/pingcap/tipb v0.0.0-20260605083900-f9f651ef5fbc
github.com/prometheus/client_golang v1.23.0
github.com/prometheus/client_model v0.6.2
github.com/prometheus/common v0.65.0
Expand Down
4 changes: 2 additions & 2 deletions go.sum
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -663,8 +663,8 @@ github.com/pingcap/log v1.1.1-0.20250917021125-19901e015dc9 h1:qG9BSvlWFEE5otQGa
github.com/pingcap/log v1.1.1-0.20250917021125-19901e015dc9/go.mod h1:ORfBOFp1eteu2odzsyaxI+b8TzJwgjwyQcGhI+9SfEA=
github.com/pingcap/sysutil v1.0.1-0.20240311050922-ae81ee01f3a5 h1:T4pXRhBflzDeAhmOQHNPRRogMYxP13V7BkYw3ZsoSfE=
github.com/pingcap/sysutil v1.0.1-0.20240311050922-ae81ee01f3a5/go.mod h1:rlimy0GcTvjiJqvD5mXTRr8O2eNZPBrcUgiWVYp9530=
github.com/pingcap/tipb v0.0.0-20260507102040-d3d6e146648f h1:ld8bQ5d0zh1B0HRbJHiaf2seZvcVV5Ug2rih70uNJMM=
github.com/pingcap/tipb v0.0.0-20260507102040-d3d6e146648f/go.mod h1:A7mrd7WHBl1o63LE2bIBGEJMTNWXqhgmYiOvMLxozfs=
github.com/pingcap/tipb v0.0.0-20260605083900-f9f651ef5fbc h1:wxolKysltFSu8gxWJBdUdWuTBoSuY3MjNIIZI5S9JLY=
github.com/pingcap/tipb v0.0.0-20260605083900-f9f651ef5fbc/go.mod h1:A7mrd7WHBl1o63LE2bIBGEJMTNWXqhgmYiOvMLxozfs=
github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c h1:+mdjkGKdHQG3305AYmdv1U2eRNDiU2ErMBj1gwrq8eQ=
github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c/go.mod h1:7rwL4CYBLnjLxUqIJNnCWiEdr3bn6IUYi15bNlnbCCU=
github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e/go.mod h1:pJLUxLENpZxwdsKMEsNbx1VGcRFpLqf3715MtcvvzbA=
Expand Down
2 changes: 1 addition & 1 deletion pkg/planner/core/casetest/rule/BUILD.bazel
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@ go_test(
],
data = glob(["testdata/**"]),
flaky = True,
shard_count = 12,
shard_count = 13,
deps = [
"//pkg/config",
"//pkg/domain",
Expand Down
55 changes: 54 additions & 1 deletion pkg/planner/core/exhaust_physical_plans.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2266,7 +2266,10 @@ func getPhysTopN(lt *logicalop.LogicalTopN, prop *property.PhysicalProperty) []b
if mppAllowed {
allTaskTypes = append(allTaskTypes, property.MppTaskType)
}
ret := make([]base.PhysicalPlan, 0, len(allTaskTypes))
ret := make([]base.PhysicalPlan, 0, len(allTaskTypes)+1)
if canUsePartialOrder4TopN(lt) {
ret = append(ret, getPhysTopNWithPartialOrderProperty(lt, prop)...)
}
for _, tp := range allTaskTypes {
resultProp := &property.PhysicalProperty{TaskTp: tp, ExpectedCnt: math.MaxFloat64, CTEProducerStatus: prop.CTEProducerStatus}
topN := PhysicalTopN{
Expand Down Expand Up @@ -2318,6 +2321,56 @@ func getPhysTopN(lt *logicalop.LogicalTopN, prop *property.PhysicalProperty) []b
return ret
}

// canUsePartialOrder4TopN checks if the TopN's child tree satisfies the supported partial-order pattern.
func canUsePartialOrder4TopN(lt *logicalop.LogicalTopN) bool {
if !lt.SCtx().GetSessionVars().IsPartialOrderedIndexForTopNEnabled() {
return false
}
if len(lt.ByItems) == 0 {
return false
}
return checkPartialOrderPattern(lt.Children()[0])
}

func checkPartialOrderPattern(plan base.LogicalPlan) bool {
switch p := plan.(type) {
case *logicalop.DataSource:
return true
case *logicalop.LogicalSelection:
return len(p.Children()) == 1 && checkPartialOrderPattern(p.Children()[0])
case *logicalop.LogicalProjection:
return len(p.Children()) == 1 && checkPartialOrderPattern(p.Children()[0])
default:
return false
}
}

func getPhysTopNWithPartialOrderProperty(lt *logicalop.LogicalTopN, prop *property.PhysicalProperty) []base.PhysicalPlan {
sortItems := make([]*property.SortItem, 0, len(lt.ByItems))
for _, byItem := range lt.ByItems {
col, ok := byItem.Expr.(*expression.Column)
if !ok {
return nil
}
sortItems = append(sortItems, &property.SortItem{Col: col, Desc: byItem.Desc})
}
partialOrderProp := &property.PhysicalProperty{
TaskTp: property.CopMultiReadTaskType,
ExpectedCnt: math.MaxFloat64,
PartialOrderInfo: &property.PartialOrderInfo{
SortItems: sortItems,
},
CTEProducerStatus: prop.CTEProducerStatus,
}
topN := PhysicalTopN{
ByItems: lt.ByItems,
PartitionBy: lt.PartitionBy,
Count: lt.Count,
Offset: lt.Offset,
}.Init(lt.SCtx(), lt.StatsInfo(), lt.QueryBlockOffset(), partialOrderProp)
return []base.PhysicalPlan{topN}
}

func getPhysLimits(lt *logicalop.LogicalTopN, prop *property.PhysicalProperty) []base.PhysicalPlan {
p, canPass := GetPropByOrderByItems(lt.ByItems)
if !canPass {
Expand Down
22 changes: 22 additions & 0 deletions pkg/planner/core/explain.go
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Original file line number Diff line number Diff line change
Expand Up @@ -483,10 +483,21 @@ func (p *PhysicalLimit) ExplainInfo() string {
}
if redact == perrors.RedactLogDisable {
fmt.Fprintf(buffer, "offset:%v, count:%v", p.Offset, p.Count)
if p.PrefixCol != nil {
fmt.Fprintf(buffer, ", prefix_col:%v, prefix_len:%v",
p.PrefixCol.ColumnExplainInfo(ectx, false), p.PrefixLen)
}
} else if redact == perrors.RedactLogMarker {
fmt.Fprintf(buffer, "offset:‹%v›, count:‹%v›", p.Offset, p.Count)
if p.PrefixCol != nil {
fmt.Fprintf(buffer, ", prefix_col:‹%v›, prefix_len:‹%v›",
p.PrefixCol.ColumnExplainInfo(ectx, false), p.PrefixLen)
}
} else if redact == perrors.RedactLogEnable {
fmt.Fprintf(buffer, "offset:?, count:?")
if p.PrefixCol != nil {
fmt.Fprintf(buffer, ", prefix_col:?, prefix_len:?")
}
}
return buffer.String()
}
Expand Down Expand Up @@ -790,10 +801,21 @@ func (p *PhysicalTopN) ExplainInfo() string {
switch p.SCtx().GetSessionVars().EnableRedactLog {
case perrors.RedactLogDisable:
fmt.Fprintf(buffer, ", offset:%v, count:%v", p.Offset, p.Count)
if p.PrefixCol != nil {
fmt.Fprintf(buffer, ", prefix_col:%v, prefix_len:%v",
p.PrefixCol.ColumnExplainInfo(ectx, false), p.PrefixLen)
}
case perrors.RedactLogMarker:
fmt.Fprintf(buffer, ", offset:‹%v›, count:‹%v›", p.Offset, p.Count)
if p.PrefixCol != nil {
fmt.Fprintf(buffer, ", prefix_col:‹%v›, prefix_len:‹%v›",
p.PrefixCol.ColumnExplainInfo(ectx, false), p.PrefixLen)
}
case perrors.RedactLogEnable:
fmt.Fprintf(buffer, ", offset:?, count:?")
if p.PrefixCol != nil {
fmt.Fprintf(buffer, ", prefix_col:?, prefix_len:?")
}
}
return buffer.String()
}
Expand Down
107 changes: 96 additions & 11 deletions pkg/planner/core/find_best_task.go
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Original file line number Diff line number Diff line change
Expand Up @@ -683,9 +683,11 @@ type candidatePath struct {
accessCondsColMap util.Col2Len // accessCondsColMap maps Column.UniqueID to column length for the columns in AccessConds.
indexCondsColMap util.Col2Len // indexCondsColMap maps Column.UniqueID to column length for the columns in AccessConds and indexFilters.
matchPropResult property.PhysicalPropMatchResult
indexJoinCols int // how many index columns are used in access conditions in this IndexJoin.
isFullRange bool // cached result of whether this path covers the full scan range.
eqOrInCount int // cached result of equalPredicateCount().
// partialOrderMatchResult records whether this path can provide partial order using prefix index.
partialOrderMatchResult property.PartialOrderMatchResult
indexJoinCols int // how many index columns are used in access conditions in this IndexJoin.
isFullRange bool // cached result of whether this path covers the full scan range.
eqOrInCount int // cached result of equalPredicateCount().
}

func compareBool(l, r bool) int {
Expand Down Expand Up @@ -1014,6 +1016,62 @@ func matchProperty(ds *logicalop.DataSource, path *util.AccessPath, prop *proper
return matchResult
}

// matchPartialOrderProperty checks if the index can provide partial order for TopN optimization.
// Unlike matchProperty, this function allows a prefix index to match ORDER BY columns.
func matchPartialOrderProperty(path *util.AccessPath, partialOrderInfo *property.PartialOrderInfo) property.PartialOrderMatchResult {
emptyResult := property.PartialOrderMatchResult{Matched: false}
if partialOrderInfo == nil || path.Index == nil || len(path.IdxCols) == 0 {
return emptyResult
}

sortItems := partialOrderInfo.SortItems
if len(sortItems) == 0 {
return emptyResult
}

allSameOrder, _ := partialOrderInfo.AllSameOrder()
if !allSameOrder {
return emptyResult
}

indexColCount := len(path.Index.Columns)
if len(path.FullIdxCols) < indexColCount || len(path.FullIdxColLens) < indexColCount {
return emptyResult
}
if indexColCount > len(sortItems) {
return emptyResult
}
if path.Index.Columns[indexColCount-1].Length == types.UnspecifiedLength {
return emptyResult
}

orderByCols := make([]*expression.Column, 0, len(sortItems))
for _, item := range sortItems {
orderByCols = append(orderByCols, item.Col)
}

for i := range indexColCount {
idxCol := path.FullIdxCols[i]
if idxCol == nil {
return emptyResult
}
if !orderByCols[i].EqualColumn(idxCol) {
return emptyResult
}
if path.FullIdxColLens[i] != types.UnspecifiedLength {
if i != indexColCount-1 {
return emptyResult
}
return property.PartialOrderMatchResult{
Matched: true,
PrefixCol: idxCol,
PrefixLen: path.FullIdxColLens[i],
}
}
}
return emptyResult
}

// GroupRangesByCols groups the ranges by the values of the columns specified by groupByColIdxs.
func GroupRangesByCols(ranges []*ranger.Range, groupByColIdxs []int) ([][]*ranger.Range, error) {
groups := make(map[string][]*ranger.Range)
Expand Down Expand Up @@ -1262,6 +1320,9 @@ func getTableCandidate(ds *logicalop.DataSource, path *util.AccessPath, prop *pr
func getIndexCandidate(ds *logicalop.DataSource, path *util.AccessPath, prop *property.PhysicalProperty) *candidatePath {
candidate := &candidatePath{path: path}
candidate.matchPropResult = matchProperty(ds, path, prop)
if ds.SCtx().GetSessionVars().IsPartialOrderedIndexForTopNEnabled() && prop.PartialOrderInfo != nil {
candidate.partialOrderMatchResult = matchPartialOrderProperty(path, prop.PartialOrderInfo)
}
candidate.accessCondsColMap = util.ExtractCol2Len(ds.SCtx().GetExprCtx().GetEvalCtx(), path.AccessConds, path.IdxCols, path.IdxColLens)
candidate.indexCondsColMap = util.ExtractCol2Len(ds.SCtx().GetExprCtx().GetEvalCtx(), append(path.AccessConds, path.IndexFilters...), path.FullIdxCols, path.FullIdxColLens)
candidate.isFullRange = path.IsFullScanRange(ds.TableInfo)
Expand Down Expand Up @@ -1337,16 +1398,32 @@ func skylinePruning(ds *logicalop.DataSource, prop *property.PhysicalProperty) [
}
var currentCandidate *candidatePath
if path.IsTablePath() {
if prop.PartialOrderInfo != nil {
continue
}
currentCandidate = getTableCandidate(ds, path, prop)
} else {
if !(len(path.AccessConds) > 0 || !prop.IsSortItemEmpty() || path.Forced || path.IsSingleScan) {
var matchPartialOrderIndex bool
if ds.SCtx().GetSessionVars().IsPartialOrderedIndexForTopNEnabled() &&
prop.PartialOrderInfo != nil {
if !matchPartialOrderProperty(path, prop.PartialOrderInfo).Matched {
continue
}
matchPartialOrderIndex = true
if path.Forced && !path.ForceNoKeepOrder {
path.ForcePartialOrder = true
}
Comment on lines +1401 to +1415
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@coderabbitai coderabbitai Bot Jun 5, 2026

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The reason will be displayed to describe this comment to others. Learn more.

⚠️ Potential issue | 🟠 Major | ⚡ Quick win

Don't persist ForcePartialOrder on the shared AccessPath.

skylinePruning() sets path.ForcePartialOrder = true in-place, but ds.PossibleAccessPaths are reused across later property explorations. After one partial-order pass marks a forced path here, a later normal pass can hit the prop.PartialOrderInfo == nil rejection in convertToIndexScan() and incorrectly discard that hinted path. Keep this flag candidate-local, or at least clear it before each pruning pass.

Minimal safe reset 
for _, path := range ds.PossibleAccessPaths {
+	path.ForcePartialOrder = false
 	// We should check whether the possible access path is valid first.
 	if path.StoreType != kv.TiFlash && prop.IsFlashProp() {
 		continue
 	}

Also applies to: 2401-2404

🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@pkg/planner/core/find_best_task.go` around lines 1401 - 1415, The review
points out that skylinePruning()/the loop is mutating the shared AccessPath by
setting path.ForcePartialOrder = true which later causes convertToIndexScan() to
reject paths when prop.PartialOrderInfo == nil; to fix, avoid persisting
ForcePartialOrder on the shared ds.PossibleAccessPaths: either operate on a
shallow copy of the AccessPath or use a candidate-local boolean (e.g.,
localForcePartialOrder) when evaluating/constructing currentCandidate in
getTableCandidate/skylinePruning rather than writing to path.ForcePartialOrder,
and if you must modify path, ensure you clear/reset path.ForcePartialOrder
before finishing each pruning pass so convertToIndexScan() sees the original
state.

}
keepIndex := len(path.AccessConds) > 0 || !prop.IsSortItemEmpty() || path.Forced || path.IsSingleScan || matchPartialOrderIndex
if !keepIndex {
continue
}
// We will use index to generate physical plan if any of the following conditions is satisfied:
// 1. This path's access cond is not nil.
// 2. We have a non-empty prop to match.
// 3. This index is forced to choose.
// 4. The needed columns are all covered by index columns(and handleCol).
// 5. It matches PartialOrderInfo physical property for partial order optimization.
currentCandidate = getIndexCandidate(ds, path, prop)
}
pruned := false
Expand Down Expand Up @@ -2314,11 +2391,15 @@ func convertToIndexScan(ds *logicalop.DataSource, prop *property.PhysicalPropert
return base.InvalidTask, nil
}
// If we need to keep order for the index scan, we should forbid the non-keep-order index scan when we try to generate the path.
if prop.IsSortItemEmpty() && candidate.path.ForceKeepOrder {
if !prop.NeedKeepOrder() && candidate.path.ForceKeepOrder {
return base.InvalidTask, nil
}
// If we don't need to keep order for the index scan, we should forbid the non-keep-order index scan when we try to generate the path.
if !prop.IsSortItemEmpty() && candidate.path.ForceNoKeepOrder {
if prop.NeedKeepOrder() && candidate.path.ForceNoKeepOrder {
return base.InvalidTask, nil
}
// If partial order is forced, reject normal full-order or no-order candidates.
if candidate.path.ForcePartialOrder && prop.PartialOrderInfo == nil {
return base.InvalidTask, nil
}
path := candidate.path
Expand All @@ -2329,6 +2410,9 @@ func convertToIndexScan(ds *logicalop.DataSource, prop *property.PhysicalPropert
tblCols: ds.TblCols,
expectCnt: uint64(prop.ExpectedCnt),
}
if candidate.partialOrderMatchResult.Matched {
cop.partialOrderMatchResult = &candidate.partialOrderMatchResult
}
cop.physPlanPartInfo = &PhysPlanPartInfo{
PruningConds: pushDownNot(ds.SCtx().GetExprCtx(), ds.AllConds),
PartitionNames: ds.PartitionNames,
Expand Down Expand Up @@ -2372,7 +2456,7 @@ func convertToIndexScan(ds *logicalop.DataSource, prop *property.PhysicalPropert
}
}
}
if candidate.matchPropResult.Matched() {
if prop.NeedKeepOrder() {
cop.keepOrder = true
if cop.tablePlan != nil && !ds.TableInfo.IsCommonHandle {
col, isNew := cop.tablePlan.(*PhysicalTableScan).appendExtraHandleCol(ds)
Expand All @@ -2387,8 +2471,9 @@ func convertToIndexScan(ds *logicalop.DataSource, prop *property.PhysicalPropert
// Case 3: both
if (ds.TableInfo.GetPartitionInfo() != nil && !is.Index.Global) ||
candidate.matchPropResult == property.PropMatchedNeedMergeSort {
byItems := make([]*util.ByItems, 0, len(prop.SortItems))
for _, si := range prop.SortItems {
sortItems := prop.GetSortItemsForKeepOrder()
byItems := make([]*util.ByItems, 0, len(sortItems))
for _, si := range sortItems {
byItems = append(byItems, &util.ByItems{
Expr: si.Col,
Desc: si.Desc,
Expand Down Expand Up @@ -3265,8 +3350,8 @@ func getOriginalPhysicalIndexScan(ds *logicalop.DataSource, prop *property.Physi
if usedStats != nil && usedStats.GetUsedInfo(is.physicalTableID) != nil {
is.usedStatsInfo = usedStats.GetUsedInfo(is.physicalTableID)
}
if isMatchProp {
is.Desc = prop.SortItems[0].Desc
if prop.NeedKeepOrder() {
is.Desc = prop.GetSortDescForKeepOrder()
is.KeepOrder = true
}
return is
Expand Down
31 changes: 13 additions & 18 deletions pkg/planner/core/hint_test.go
View file
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Original file line number Diff line number Diff line change
Expand Up @@ -90,35 +90,30 @@ func TestSetVarPartialOrderedIndexForTopN(t *testing.T) {
testKit.MustExec(`use test`)

// Test default value
testKit.MustQuery(`select @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("0"))
testKit.MustQuery(`select @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("DISABLE"))

// Test set_var hint changes the value during query execution
testKit.MustExec(`set @@tidb_opt_partial_ordered_index_for_topn = 0`)
testKit.MustQuery(`select /*+ set_var(tidb_opt_partial_ordered_index_for_topn=ON) */ @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("1"))
testKit.MustExec(`set @@tidb_opt_partial_ordered_index_for_topn = DISABLE`)
testKit.MustQuery(`select /*+ set_var(tidb_opt_partial_ordered_index_for_topn=COST) */ @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("COST"))
// Value should be restored after query
testKit.MustQuery(`select @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("0"))
testKit.MustQuery(`select @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("DISABLE"))

// Test set_var hint with OFF
testKit.MustExec(`set @@tidb_opt_partial_ordered_index_for_topn = 1`)
testKit.MustQuery(`select /*+ set_var(tidb_opt_partial_ordered_index_for_topn=OFF) */ @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("0"))
testKit.MustExec(`set @@tidb_opt_partial_ordered_index_for_topn = COST`)
testKit.MustQuery(`select /*+ set_var(tidb_opt_partial_ordered_index_for_topn=DISABLE) */ @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("DISABLE"))
// Value should be restored after query
testKit.MustQuery(`select @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("1"))

// Test set_var hint with numeric values
testKit.MustExec(`set @@tidb_opt_partial_ordered_index_for_topn = 0`)
testKit.MustQuery(`select /*+ set_var(tidb_opt_partial_ordered_index_for_topn=1) */ @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("1"))
testKit.MustQuery(`select @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("0"))
testKit.MustQuery(`select @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("COST"))

// Test set_var hint with multiple queries
testKit.MustExec(`create table t(a int, b varchar(10), index idx_b(b(5)));`)
testKit.MustExec(`set @@tidb_opt_partial_ordered_index_for_topn = 0`)
testKit.MustExec(`select /*+ set_var(tidb_opt_partial_ordered_index_for_topn=ON) */ * from t order by b limit 10;`)
testKit.MustQuery(`select @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("0"))
testKit.MustExec(`set @@tidb_opt_partial_ordered_index_for_topn = DISABLE`)
testKit.MustExec(`select /*+ set_var(tidb_opt_partial_ordered_index_for_topn=COST) */ * from t order by b limit 10;`)
testKit.MustQuery(`select @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("DISABLE"))

// Test with EXPLAIN (should not change the value)
testKit.MustExec(`set @@tidb_opt_partial_ordered_index_for_topn = 0`)
testKit.MustExec(`explain select /*+ set_var(tidb_opt_partial_ordered_index_for_topn=ON) */ * from t order by b limit 10;`)
testKit.MustQuery(`select @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("0"))
testKit.MustExec(`set @@tidb_opt_partial_ordered_index_for_topn = DISABLE`)
testKit.MustExec(`explain select /*+ set_var(tidb_opt_partial_ordered_index_for_topn=COST) */ * from t order by b limit 10;`)
testKit.MustQuery(`select @@tidb_opt_partial_ordered_index_for_topn`).Check(testkit.Rows("DISABLE"))
})
}

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