sql: incorporate lookupExpr cpu cost into cost model

Release note (sql): improve cost model to include cpu cost of lookupExprs used by lookup joins.
cockroachdb · Jun 25, 2021 · da760c3 · da760c3
1 parent 63ac8bd
commit da760c3
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Showing 2 changed files with 18 additions and 6 deletions.
diff --git a/pkg/sql/opt/xform/coster.go b/pkg/sql/opt/xform/coster.go
@@ -760,7 +760,7 @@ func (c *coster) computeMergeJoinCost(join *memo.MergeJoinExpr) memo.Cost {
 func (c *coster) computeIndexJoinCost(
 	join *memo.IndexJoinExpr, required *physical.Required,
 ) memo.Cost {
-	return c.computeIndexLookupJoinCost(
+	cost, _ := c.computeIndexLookupJoinCost(
 		join,
 		required,
 		true, /* lookupColsAreTableKey */
@@ -771,6 +771,7 @@ func (c *coster) computeIndexJoinCost(
 		memo.JoinFlags(0),
 		false, /* localityOptimized */
 	)
+	return cost
 }
 
 func (c *coster) computeLookupJoinCost(
@@ -779,7 +780,8 @@ func (c *coster) computeLookupJoinCost(
 	if join.LookupJoinPrivate.Flags.Has(memo.DisallowLookupJoinIntoRight) {
 		return hugeCost
 	}
-	return c.computeIndexLookupJoinCost(
+
+	cost, lookupCount := c.computeIndexLookupJoinCost(
 		join,
 		required,
 		join.LookupColsAreTableKey,
@@ -790,6 +792,16 @@ func (c *coster) computeLookupJoinCost(
 		join.Flags,
 		join.LocalityOptimized,
 	)
+
+	// If we have extra lookupExprs beyond whats in the on conditions add those
+	// as an extra cpu cost since the joinreader machinery isn't free.
+	extraLookupJoinConditions := join.LookupExpr.Difference(join.On)
+	if len(extraLookupJoinConditions) > 0 {
+		extraCost := memo.Cost(lookupCount) * cpuCostFactor * memo.Cost(extraLookupJoinConditions.ChildCount())
+		cost += extraCost
+	}
+
+	return cost
 }
 
 func (c *coster) computeIndexLookupJoinCost(
@@ -802,7 +814,7 @@ func (c *coster) computeIndexLookupJoinCost(
 	index cat.IndexOrdinal,
 	flags memo.JoinFlags,
 	localityOptimized bool,
-) memo.Cost {
+) (memo.Cost, float64) {
 	input := join.Child(0).(memo.RelExpr)
 	lookupCount := input.Relational().Stats.RowCount
 
@@ -880,7 +892,7 @@ func (c *coster) computeIndexLookupJoinCost(
 	if localityOptimized {
 		cost /= 2.5
 	}
-	return cost
+	return cost, lookupCount
 }
 
 func (c *coster) computeInvertedJoinCost(

diff --git a/pkg/sql/opt/xform/testdata/coster/zone b/pkg/sql/opt/xform/testdata/coster/zone
@@ -752,7 +752,7 @@ anti-join (lookup abc_part@bc_idx [as=a2])
  │         └── a2.r:7 = 'west' [outer=(7), constraints=(/7: [/'west' - /'west']; tight), fd=()-->(7)]
  ├── cardinality: [0 - 1]
  ├── stats: [rows=1e-10]
- ├── cost: 18.0617898
+ ├── cost: 18.0980078
  ├── key: ()
  ├── fd: ()-->(1-4)
  ├── anti-join (lookup abc_part@bc_idx [as=a2])
@@ -763,7 +763,7 @@ anti-join (lookup abc_part@bc_idx [as=a2])
  │    │         └── a2.r:7 = 'east' [outer=(7), constraints=(/7: [/'east' - /'east']; tight), fd=()-->(7)]
  │    ├── cardinality: [0 - 1]
  │    ├── stats: [rows=0.900900001, distinct(1)=0.89738934, null(1)=0, distinct(2)=0.900900001, null(2)=0, distinct(3)=0.900900001, null(3)=0, distinct(4)=0.900900001, null(4)=0]
- │    ├── cost: 10.7686007
+ │    ├── cost: 10.7868007
  │    ├── key: ()
  │    ├── fd: ()-->(1-4)
  │    ├── locality-optimized-search