Use buffer.Pool for sql.Row allocations

sql/aggregates.go

@@ -109,7 +109,7 @@ type WindowFrame interface {
 	StartCurrentRow() bool
 	// EndCurrentRow returns whether a frame end is CURRENT ROW
 	EndCurrentRow() bool
-	// StartNFollowing returns a frame's start preceding Expression or nil
+	// StartNPreceding returns a frame's start preceding Expression or nil
 	StartNPreceding() Expression
 	// StartNFollowing returns a frame's start following Expression or nil
 	StartNFollowing() Expression

sql/rowexec/agg.go

@@ -238,8 +238,9 @@ func (i *groupByGroupingIter) Dispose() {
 }
 
 func groupingKey(ctx *sql.Context, exprs []sql.Expression, row sql.Row) (uint64, error) {
-	var keyRow = make(sql.Row, len(exprs))
 	var keySch = make(sql.Schema, len(exprs))
+	keyRow := sql.GetRow(len(exprs))
+	defer sql.PutRow(keyRow)
 	for i, expr := range exprs {
 		v, err := expr.Eval(ctx, row)
 		if err != nil {

sql/rowexec/merge_join.go

@@ -47,7 +47,6 @@ func newMergeJoinIter(ctx *sql.Context, b sql.NodeExecBuilder, j *plan.JoinNode,
 	}
 
 	fullRow := make(sql.Row, len(row)+len(j.Left().Schema())+len(j.Right().Schema()))
-	fullRow[0] = row
 	if len(row) > 0 {
 		copy(fullRow[0:], row[:])
 	}
@@ -376,7 +375,7 @@ func (i *mergeJoinIter) incMatch(ctx *sql.Context) error {
 
 	if !i.leftDone {
 		// rightBuf has already been validated, we don't need compare
-		copySubslice(i.fullRow, i.rightBuf[i.bufI], i.scopeLen+i.parentLen+i.leftRowLen)
+		copy(i.fullRow[i.scopeLen+i.parentLen+i.leftRowLen:], i.rightBuf[i.bufI])
 		i.bufI++
 		return nil
 	}
@@ -394,16 +393,16 @@ func (i *mergeJoinIter) incMatch(ctx *sql.Context) error {
 		if i.lojFinalize() {
 			// left joins expect the left row in |i.fullRow| as long
 			// as the left iter is not exhausted.
-			copySubslice(i.fullRow, i.leftPeek, i.scopeLen+i.parentLen)
+			copy(i.fullRow[i.scopeLen+i.parentLen:], i.leftPeek)
 		}
 		return nil
 	}
 
 	// both lookaheads fail the join condition. Drain
 	// lookahead rows / increment both iterators.
 	i.matchIncLeft = true
-	copySubslice(i.fullRow, i.leftPeek, i.scopeLen+i.parentLen)
-	copySubslice(i.fullRow, i.rightPeek, i.scopeLen+i.parentLen+i.leftRowLen)
+	copy(i.fullRow[i.scopeLen+i.parentLen:], i.leftPeek)
+	copy(i.fullRow[i.scopeLen+i.parentLen+i.leftRowLen:], i.rightPeek)
 
 	return nil
 }
@@ -454,7 +453,7 @@ func (i *mergeJoinIter) resetMatchState() {
 // no match, no lookahead row, and no error.
 func (i *mergeJoinIter) peekMatch(ctx *sql.Context, iter sql.RowIter) (bool, sql.Row, error) {
 	var off int
-	var restore sql.Row
+	var restore sql.Row // TODO: rowBuffer?
 	switch iter {
 	case i.left:
 		off = i.scopeLen + i.parentLen
@@ -477,17 +476,17 @@ func (i *mergeJoinIter) peekMatch(ctx *sql.Context, iter sql.RowIter) (bool, sql
 	}
 
 	// check if lookahead valid
-	copySubslice(i.fullRow, peek, off)
+	copy(i.fullRow[off:], peek)
 	res, err := i.cmp.Compare(ctx, i.fullRow)
 	if expression.ErrNilOperand.Is(err) {
 		// revert change to output row if no match
-		copySubslice(i.fullRow, restore, off)
+		copy(i.fullRow[off:], restore)
 	} else if err != nil {
 		return false, nil, err
 	}
 	if res != 0 {
 		// revert change to output row if no match
-		copySubslice(i.fullRow, restore, off)
+		copy(i.fullRow[off:], restore)
 	}
 	return res == 0, peek, nil
 }

sql/rows.go

@@ -18,6 +18,7 @@ import (
 	"fmt"
 	"io"
 	"strings"
+	"sync"
 
 	"github.com/dolthub/vitess/go/vt/proto/query"
 
@@ -69,6 +70,22 @@ func (r Row) Equals(ctx *Context, row Row, schema Schema) (bool, error) {
 	return true, nil
 }
 
+// TODO: find a proper place for this
+var rowBuffers = sync.Pool{
+	New: func() interface{} {
+		return make(Row, 0, 4096) // max number of columns for a table
+	},
+}
+
+func GetRow(length int) Row {
+	row := rowBuffers.Get().(Row)
+	return row[:length]
+}
+
+func PutRow(row Row) {
+	rowBuffers.Put(row[:0])
+}
+
 // FormatRow returns a formatted string representing this row's values
 func FormatRow(row Row) string {
 	var sb strings.Builder