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planner: update the cost formula of IndexJoin+IndexLookup (#39617) #39652

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planner: update the cost formula of IndexJoin+IndexLookup (#39617) #39652

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5 changes: 5 additions & 0 deletions planner/core/plan_cost_ver2.go
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Original file line number Diff line number Diff line change
Expand Up @@ -593,6 +593,11 @@ func (p *PhysicalIndexJoin) getIndexJoinCostVer2(taskType property.TaskType, opt
// Use an empirical value batchRatio to handle this now.
// TODO: remove this empirical value.
batchRatio := 6.0
if _, isIndexLookUp := probe.(*PhysicalIndexLookUpReader); isIndexLookUp {
// IndexJoin + IndexLookUp has the risks to cause massive double-read requests,
// set the batchRatio to a lower value in this case for safety.
batchRatio = 1.5
}
probeCost := divCostVer2(mulCostVer2(probeChildCost, buildRows), batchRatio)

p.planCostVer2 = sumCostVer2(startCost, buildChildCost, buildFilterCost, buildTaskCost, divCostVer2(sumCostVer2(probeCost, probeFilterCost, hashTableCost), probeConcurrency))
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