planner: adjust estimated rows to account for modified rows (#50970)

close #47523

Author: terry1purcell

pkg/planner/cardinality/row_count_column.go

@@ -282,15 +282,17 @@ func GetColumnRowCount(sctx context.PlanContext, c *statistics.Column, ranges []
 		cnt = mathutil.Clamp(cnt, 0, c.TotalRowCount())
 
 		// If the current table row count has changed, we should scale the row count accordingly.
-		cnt *= c.GetIncreaseFactor(realtimeRowCount)
+		increaseFactor := c.GetIncreaseFactor(realtimeRowCount)
+		cnt *= increaseFactor
 
-		histNDV := c.NDV
-		if c.StatsVer == statistics.Version2 {
-			histNDV = histNDV - int64(c.TopN.Num())
-		}
 		// handling the out-of-range part
 		if (c.OutOfRange(lowVal) && !lowVal.IsNull()) || c.OutOfRange(highVal) {
-			cnt += c.Histogram.OutOfRangeRowCount(sctx, &lowVal, &highVal, modifyCount, histNDV)
+			histNDV := c.NDV
+			// Exclude the TopN
+			if c.StatsVer == statistics.Version2 {
+				histNDV -= int64(c.TopN.Num())
+			}
+			cnt += c.Histogram.OutOfRangeRowCount(sctx, &lowVal, &highVal, modifyCount, histNDV, increaseFactor)
 		}
 
 		if debugTrace {

pkg/planner/cardinality/row_count_index.go

@@ -222,7 +222,7 @@ func getIndexRowCountForStatsV2(sctx context.PlanContext, idx *statistics.Index,
 		defer debugtrace.LeaveContextCommon(sctx)
 	}
 	totalCount := float64(0)
-	isSingleCol := len(idx.Info.Columns) == 1
+	isSingleColIdx := len(idx.Info.Columns) == 1
 	for _, indexRange := range indexRanges {
 		var count float64
 		lb, err := codec.EncodeKey(sc.TimeZone(), nil, indexRange.LowVal...)
@@ -278,7 +278,7 @@ func getIndexRowCountForStatsV2(sctx context.PlanContext, idx *statistics.Index,
 		l := types.NewBytesDatum(lb)
 		r := types.NewBytesDatum(rb)
 		lowIsNull := bytes.Equal(lb, nullKeyBytes)
-		if isSingleCol && lowIsNull {
+		if isSingleColIdx && lowIsNull {
 			count += float64(idx.Histogram.NullCount)
 		}
 		expBackoffSuccess := false
@@ -325,15 +325,24 @@ func getIndexRowCountForStatsV2(sctx context.PlanContext, idx *statistics.Index,
 		}
 
 		// If the current table row count has changed, we should scale the row count accordingly.
-		count *= idx.GetIncreaseFactor(realtimeRowCount)
+		increaseFactor := idx.GetIncreaseFactor(realtimeRowCount)
+		count *= increaseFactor
 
-		histNDV := idx.NDV
-		if idx.StatsVer == statistics.Version2 {
-			histNDV = histNDV - int64(idx.TopN.Num())
-		}
 		// handling the out-of-range part
-		if (outOfRangeOnIndex(idx, l) && !(isSingleCol && lowIsNull)) || outOfRangeOnIndex(idx, r) {
-			count += idx.Histogram.OutOfRangeRowCount(sctx, &l, &r, modifyCount, histNDV)
+		if (outOfRangeOnIndex(idx, l) && !(isSingleColIdx && lowIsNull)) || outOfRangeOnIndex(idx, r) {
+			histNDV := idx.NDV
+			// Exclude the TopN in Stats Version 2
+			if idx.StatsVer == statistics.Version2 {
+				c, ok := coll.Columns[idx.Histogram.ID]
+				// If this is single column of a multi-column index - use the column's NDV rather than index NDV
+				isSingleColRange := len(indexRange.LowVal) == len(indexRange.HighVal) && len(indexRange.LowVal) == 1
+				if isSingleColRange && !isSingleColIdx && ok && c != nil && c.Histogram.NDV > 0 {
+					histNDV = c.Histogram.NDV - int64(c.TopN.Num())
+				} else {
+					histNDV -= int64(idx.TopN.Num())
+				}
+			}
+			count += idx.Histogram.OutOfRangeRowCount(sctx, &l, &r, modifyCount, histNDV, increaseFactor)
 		}
 
 		if debugTrace {

pkg/planner/cardinality/testdata/cardinality_suite_out.json

@@ -24,7 +24,7 @@
       {
         "Start": 800,
         "End": 900,
-        "Count": 723.504166655054
+        "Count": 735.504166655054
       },
       {
         "Start": 900,
@@ -79,7 +79,7 @@
       {
         "Start": 800,
         "End": 1000,
-        "Count": 1181.696869573942
+        "Count": 1193.696869573942
       },
       {
         "Start": 900,
@@ -104,7 +104,7 @@
       {
         "Start": 200,
         "End": 400,
-        "Count": 1190.2788209899081
+        "Count": 1237.5288209899081
       },
       {
         "Start": 200,

pkg/statistics/histogram.go

@@ -937,7 +937,7 @@ func (hg *Histogram) OutOfRange(val types.Datum) bool {
 func (hg *Histogram) OutOfRangeRowCount(
 	sctx context.PlanContext,
 	lDatum, rDatum *types.Datum,
-	modifyCount, histNDV int64,
+	modifyCount, histNDV int64, increaseFactor float64,
 ) (result float64) {
 	debugTrace := sctx.GetSessionVars().StmtCtx.EnableOptimizerDebugTrace
 	if debugTrace {
@@ -1052,38 +1052,35 @@ func (hg *Histogram) OutOfRangeRowCount(
 		rightPercent = (math.Pow(boundR-actualL, 2) - math.Pow(boundR-actualR, 2)) / math.Pow(histWidth, 2)
 	}
 
-	totalPercent := leftPercent*0.5 + rightPercent*0.5
-	if totalPercent > 1 {
-		totalPercent = 1
-	}
+	totalPercent := min(leftPercent*0.5+rightPercent*0.5, 1.0)
 	rowCount = totalPercent * hg.NotNullCount()
 
-	// Upper bound logic
+	// Upper & lower bound logic.
+	upperBound := rowCount
+	if histNDV > 0 {
+		upperBound = hg.NotNullCount() / float64(histNDV)
+	}
 
 	allowUseModifyCount := sctx.GetSessionVars().GetOptObjective() != variable.OptObjectiveDeterminate
-	// Use the modifyCount as the upper bound. Note that modifyCount contains insert, delete and update. So this is
-	// a rather loose upper bound.
-	// There are some scenarios where we need to handle out-of-range estimation after both insert and delete happen.
-	// But we don't know how many increases are in the modifyCount. So we have to use this loose bound to ensure it
-	// can produce a reasonable results in this scenario.
-	if rowCount > float64(modifyCount) && allowUseModifyCount {
-		return float64(modifyCount)
-	}
-
-	// In OptObjectiveDeterminate mode, we can't rely on the modify count anymore.
-	// An upper bound is necessary to make the estimation make sense for predicates with bound on only one end, like a > 1.
-	// But it's impossible to have a reliable upper bound in all cases.
-	// We use 1/NDV here (only the Histogram part is considered) and it seems reasonable and good enough for now.
+
 	if !allowUseModifyCount {
-		var upperBound float64
-		if histNDV > 0 {
-			upperBound = hg.NotNullCount() / float64(histNDV)
-		}
-		if rowCount > upperBound {
-			return upperBound
-		}
+		// In OptObjectiveDeterminate mode, we can't rely on the modify count anymore.
+		// An upper bound is necessary to make the estimation make sense for predicates with bound on only one end, like a > 1.
+		// We use 1/NDV here (only the Histogram part is considered) and it seems reasonable and good enough for now.
+		return min(rowCount, upperBound)
+	}
+
+	// If the modifyCount is large (compared to original table rows), then any out of range estimate is unreliable.
+	// Assume at least 1/NDV is returned
+	if float64(modifyCount) > hg.NotNullCount() && rowCount < upperBound {
+		rowCount = upperBound
+	} else if rowCount < upperBound {
+		// Adjust by increaseFactor if our estimate is low
+		rowCount *= increaseFactor
 	}
-	return rowCount
+
+	// Use modifyCount as a final bound
+	return min(rowCount, float64(modifyCount))
 }
 
 // Copy deep copies the histogram.