Merge #138246

138246: opt/exec: reduce allocations for counting join algorithms and types r=mgartner a=mgartner

Arrays embedded in `execbuilder.Builder` are now used instead of maps to
keep track of the count of join algorithms and types used in a query
plan. This reduces allocations and overhead of using a hash map.

We now only track up to 255 of each algorithm and type. This seems like
a suitable limitation because it should be extremely rare for a query to
have so many joins and these metrics don't need to be completely
accurate - they are meant to provide a rough picture of how common
each join algorithm and type is in practice.

Epic: None

Release note: None


Co-authored-by: Marcus Gartner <[email protected]>

pkg/sql/instrumentation.go

@@ -19,7 +19,6 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/settings"
 	"github.com/cockroachdb/cockroach/pkg/sql/appstatspb"
 	"github.com/cockroachdb/cockroach/pkg/sql/catalog/colinfo"
-	"github.com/cockroachdb/cockroach/pkg/sql/catalog/descpb"
 	"github.com/cockroachdb/cockroach/pkg/sql/execinfra"
 	"github.com/cockroachdb/cockroach/pkg/sql/execinfrapb"
 	"github.com/cockroachdb/cockroach/pkg/sql/execstats"
@@ -215,12 +214,12 @@ type instrumentationHelper struct {
 	nanosSinceStatsForecasted time.Duration
 
 	// joinTypeCounts records the number of times each type of logical join was
-	// used in the query.
-	joinTypeCounts map[descpb.JoinType]int
+	// used in the query, up to 255.
+	joinTypeCounts [execbuilder.NumRecordedJoinTypes]uint8
 
-	// joinAlgorithmCounts records the number of times each type of join algorithm
-	// was used in the query.
-	joinAlgorithmCounts map[exec.JoinAlgorithm]int
+	// joinAlgorithmCounts records the number of times each type of join
+	// algorithm was used in the query, up to 255.
+	joinAlgorithmCounts [exec.NumJoinAlgorithms]uint8
 
 	// scanCounts records the number of times scans were used in the query.
 	scanCounts [exec.NumScanCountTypes]int

pkg/sql/opt/exec/execbuilder/builder.go

@@ -11,7 +11,6 @@ import (
 	"strconv"
 	"time"
 
-	"github.com/cockroachdb/cockroach/pkg/sql/catalog/descpb"
 	"github.com/cockroachdb/cockroach/pkg/sql/opt"
 	"github.com/cockroachdb/cockroach/pkg/sql/opt/cat"
 	"github.com/cockroachdb/cockroach/pkg/sql/opt/exec"
@@ -38,7 +37,13 @@ var parallelScanResultThreshold = uint64(metamorphic.ConstantWithTestRange(
 	parallelScanResultThresholdProductionValue, /* max */
 ))
 
-const parallelScanResultThresholdProductionValue = 10000
+const (
+	parallelScanResultThresholdProductionValue = 10000
+
+	// numJoinTypes includes all join types except for descpb.RightSemiJoin and
+	// descpb.RightAntiJoin, which are recorded as left joins.
+	NumRecordedJoinTypes = 8
+)
 
 func getParallelScanResultThreshold(forceProductionValue bool) uint64 {
 	if forceProductionValue {
@@ -154,12 +159,12 @@ type Builder struct {
 	NanosSinceStatsForecasted time.Duration
 
 	// JoinTypeCounts records the number of times each type of logical join was
-	// used in the query.
-	JoinTypeCounts map[descpb.JoinType]int
+	// used in the query, up to 255.
+	JoinTypeCounts [NumRecordedJoinTypes]uint8
 
-	// JoinAlgorithmCounts records the number of times each type of join algorithm
-	// was used in the query.
-	JoinAlgorithmCounts map[exec.JoinAlgorithm]int
+	// JoinAlgorithmCounts records the number of times each type of join
+	// algorithm was used in the query, up to 255.
+	JoinAlgorithmCounts [exec.NumJoinAlgorithms]uint8
 
 	// ScanCounts records the number of times scans were used in the query.
 	ScanCounts [exec.NumScanCountTypes]int

pkg/sql/opt/exec/execbuilder/relational.go

@@ -3948,10 +3948,6 @@ func (b *Builder) statementTag(expr memo.RelExpr) string {
 // recordJoinType increments the counter for the given join type for telemetry
 // reporting.
 func (b *Builder) recordJoinType(joinType descpb.JoinType) {
-	if b.JoinTypeCounts == nil {
-		const numJoinTypes = 7
-		b.JoinTypeCounts = make(map[descpb.JoinType]int, numJoinTypes)
-	}
 	// Don't bother distinguishing between left and right.
 	switch joinType {
 	case descpb.RightOuterJoin:
@@ -3961,16 +3957,17 @@ func (b *Builder) recordJoinType(joinType descpb.JoinType) {
 	case descpb.RightAntiJoin:
 		joinType = descpb.LeftAntiJoin
 	}
-	b.JoinTypeCounts[joinType]++
+	if b.JoinTypeCounts[joinType]+1 > b.JoinTypeCounts[joinType] {
+		b.JoinTypeCounts[joinType]++
+	}
 }
 
 // recordJoinAlgorithm increments the counter for the given join algorithm for
 // telemetry reporting.
 func (b *Builder) recordJoinAlgorithm(joinAlgorithm exec.JoinAlgorithm) {
-	if b.JoinAlgorithmCounts == nil {
-		b.JoinAlgorithmCounts = make(map[exec.JoinAlgorithm]int, exec.NumJoinAlgorithms)
+	if b.JoinAlgorithmCounts[joinAlgorithm]+1 > b.JoinAlgorithmCounts[joinAlgorithm] {
+		b.JoinAlgorithmCounts[joinAlgorithm]++
 	}
-	b.JoinAlgorithmCounts[joinAlgorithm]++
 }
 
 // boundedStalenessAllowList contains the operators that may be used with