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planner: short-circuit cross join with limit via pushdown #67568

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planner: short-circuit cross join with limit via pushdown #67568

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35 changes: 35 additions & 0 deletions pkg/planner/core/operator/logicalop/logical_join.go
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Original file line number Diff line number Diff line change
Expand Up @@ -510,6 +510,27 @@ func (p *LogicalJoin) PushDownTopN(topNLogicalPlan base.LogicalPlan) base.Logica
case base.RightOuterJoin:
p.Children()[1], topnEliminated = p.pushDownTopNToChild(topN, 1)
p.Children()[0] = p.Children()[0].PushDownTopN(nil)
case base.InnerJoin:
if p.canPushLimitDownToCartesianChildren(topN) {
limitCount, carry := bits.Add64(topN.Count, topN.Offset, 0)
if carry > 0 {
limitCount = math.MaxUint64
}
leftLimit := LogicalTopN{
Count: limitCount,
Offset: 0,
PreferLimitToCop: topN.PreferLimitToCop,
}.Init(topN.SCtx(), topN.QueryBlockOffset())
rightLimit := LogicalTopN{
Count: limitCount,
Offset: 0,
PreferLimitToCop: topN.PreferLimitToCop,
}.Init(topN.SCtx(), topN.QueryBlockOffset())
p.Children()[0] = p.Children()[0].PushDownTopN(leftLimit)
p.Children()[1] = p.Children()[1].PushDownTopN(rightLimit)
return topN.AttachChild(p.Self())
}
return p.BaseLogicalPlan.PushDownTopN(topN)
default:
return p.BaseLogicalPlan.PushDownTopN(topN)
}
Expand All @@ -531,6 +552,20 @@ func (p *LogicalJoin) PushDownTopN(topNLogicalPlan base.LogicalPlan) base.Logica
return p.Self()
}

func (p *LogicalJoin) canPushLimitDownToCartesianChildren(topN *LogicalTopN) bool {
if topN == nil || !topN.IsLimit() {
return false
}
if _, isApply := p.Self().(*LogicalApply); isApply {
return false
}
return len(p.EqualConditions) == 0 &&
len(p.NAEQConditions) == 0 &&
len(p.LeftConditions) == 0 &&
len(p.RightConditions) == 0 &&
len(p.OtherConditions) == 0
}

// DeriveTopN inherits the BaseLogicalPlan.LogicalPlan.<6th> implementation.

// PredicateSimplification inherits the BaseLogicalPlan.LogicalPlan.<7th> implementation.
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2 changes: 1 addition & 1 deletion pkg/planner/core/testdata/plan_suite_unexported_out.json
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Original file line number Diff line number Diff line change
Expand Up @@ -148,7 +148,7 @@
"DataScan(t)->Aggr(count(test.t.b),firstrow(test.t.a))->Limit->Projection",
"DataScan(t)->Aggr(count(test.t.b),firstrow(test.t.a),firstrow(test.t.c))->TopN([test.t.c],0,5)->Projection",
"Join{DataScan(t)->DataScan(s)}->TopN([test.t.a],0,5)->Projection",
"Join{DataScan(t)->DataScan(s)}->Limit->Projection",
"Join{DataScan(t)->Limit->DataScan(s)->Limit}->Limit->Projection",
"DataScan(t)->Projection->TopN([Column#14 true],0,1)->Projection",
"Join{DataScan(t)->TopN([test.t.a],0,5)->DataScan(s)}(test.t.a,test.t.a)->Sort->Projection",
"Join{DataScan(t)->TopN([test.t.a],5,5)->DataScan(s)}(test.t.a,test.t.a)->Sort->Projection",
Expand Down