sql: avoid copying ColumnDescriptors in initColsForScan

pkg/sql/distsql_physical_planner.go

@@ -920,7 +920,7 @@ func tableOrdinal(
 // toTableOrdinals returns a mapping from column ordinals in cols to table
 // reader column ordinals.
 func toTableOrdinals(
-	cols []sqlbase.ColumnDescriptor,
+	cols []*sqlbase.ColumnDescriptor,
 	desc *sqlbase.ImmutableTableDescriptor,
 	visibility execinfrapb.ScanVisibility,
 ) []int {
@@ -934,17 +934,17 @@ func toTableOrdinals(
 // getOutputColumnsFromColsForScan returns the indices of the columns that are
 // returned by a scanNode or a tableReader.
 // If remap is not nil, the column ordinals are remapped accordingly.
-func getOutputColumnsFromColsForScan(cols []sqlbase.ColumnDescriptor, remap []int) []uint32 {
-	outputColumns := make([]uint32, 0, len(cols))
+func getOutputColumnsFromColsForScan(cols []*sqlbase.ColumnDescriptor, remap []int) []uint32 {
+	outputColumns := make([]uint32, len(cols))
 	// TODO(radu): if we have a scan with a filter, cols will include the
 	// columns needed for the filter, even if they aren't needed for the next
 	// stage.
-	for i := 0; i < len(cols); i++ {
+	for i := range outputColumns {
 		colIdx := i
 		if remap != nil {
 			colIdx = remap[i]
 		}
-		outputColumns = append(outputColumns, uint32(colIdx))
+		outputColumns[i] = uint32(colIdx)
 	}
 	return outputColumns
 }
@@ -1085,7 +1085,7 @@ type tableReaderPlanningInfo struct {
 	maxResults             uint64
 	estimatedRowCount      uint64
 	reqOrdering            ReqOrdering
-	cols                   []sqlbase.ColumnDescriptor
+	cols                   []*sqlbase.ColumnDescriptor
 	colsToTableOrdrinalMap []int
 }
 

pkg/sql/distsql_spec_exec_factory.go

@@ -123,7 +123,7 @@ func (e *distSQLSpecExecFactory) ConstructScan(
 	if err != nil {
 		return nil, err
 	}
-	p.ResultColumns = sqlbase.ResultColumnsFromColDescs(tabDesc.GetID(), cols)
+	p.ResultColumns = sqlbase.ResultColumnsFromColDescPtrs(tabDesc.GetID(), cols)
 
 	if indexConstraint != nil && indexConstraint.IsContradiction() {
 		// TODO(yuzefovich): once ConstructValues is implemented, consider

pkg/sql/scan.go

@@ -57,7 +57,7 @@ type scanNode struct {
 	// be gained (e.g. for tables with wide rows) by reading only certain
 	// columns from KV using point lookups instead of a single range lookup for
 	// the entire row.
-	cols []sqlbase.ColumnDescriptor
+	cols []*sqlbase.ColumnDescriptor
 	// There is a 1-1 correspondence between cols and resultColumns.
 	resultColumns sqlbase.ResultColumns
 
@@ -280,12 +280,12 @@ func (n *scanNode) lookupSpecifiedIndex(indexFlags *tree.IndexFlags) error {
 // initColsForScan initializes cols according to desc and colCfg.
 func initColsForScan(
 	desc *sqlbase.ImmutableTableDescriptor, colCfg scanColumnsConfig,
-) (cols []sqlbase.ColumnDescriptor, err error) {
+) (cols []*sqlbase.ColumnDescriptor, err error) {
 	if colCfg.wantedColumns == nil {
 		return nil, errors.AssertionFailedf("unexpectedly wantedColumns is nil")
 	}
 
-	cols = make([]sqlbase.ColumnDescriptor, 0, len(desc.ReadableColumns))
+	cols = make([]*sqlbase.ColumnDescriptor, 0, len(desc.ReadableColumns))
 	for _, wc := range colCfg.wantedColumns {
 		var c *sqlbase.ColumnDescriptor
 		var err error
@@ -298,7 +298,7 @@ func initColsForScan(
 			return cols, err
 		}
 
-		cols = append(cols, *c)
+		cols = append(cols, c)
 	}
 
 	if colCfg.addUnwantedAsHidden {
@@ -312,9 +312,12 @@ func initColsForScan(
 				}
 			}
 			if !found {
+				// NB: we could amortize this allocation using a second slice,
+				// but addUnwantedAsHidden is only used by scrub, so doing so
+				// doesn't seem worth it.
 				col := *c
 				col.Hidden = true
-				cols = append(cols, col)
+				cols = append(cols, &col)
 			}
 		}
 	}
@@ -334,7 +337,7 @@ func (n *scanNode) initDescDefaults(colCfg scanColumnsConfig) error {
 	}
 
 	// Set up the rest of the scanNode.
-	n.resultColumns = sqlbase.ResultColumnsFromColDescs(n.desc.GetID(), n.cols)
+	n.resultColumns = sqlbase.ResultColumnsFromColDescPtrs(n.desc.GetID(), n.cols)
 	n.colIdxMap = make(map[sqlbase.ColumnID]int, len(n.cols))
 	for i, c := range n.cols {
 		n.colIdxMap[c.ID] = i

pkg/sql/sqlbase/result_columns.go

@@ -36,28 +36,37 @@ type ResultColumn struct {
 // describe the column types of a table.
 type ResultColumns []ResultColumn
 
-// ResultColumnsFromColDescs converts ColumnDescriptors to ResultColumns.
+// ResultColumnsFromColDescs converts []ColumnDescriptor to []ResultColumn.
 func ResultColumnsFromColDescs(tableID ID, colDescs []ColumnDescriptor) ResultColumns {
-	cols := make(ResultColumns, 0, len(colDescs))
-	for i := range colDescs {
-		// Convert the ColumnDescriptor to ResultColumn.
-		colDesc := &colDescs[i]
+	return resultColumnsFromColDescs(tableID, len(colDescs), func(i int) *ColumnDescriptor {
+		return &colDescs[i]
+	})
+}
+
+// ResultColumnsFromColDescPtrs converts []*ColumnDescriptor to []ResultColumn.
+func ResultColumnsFromColDescPtrs(tableID ID, colDescs []*ColumnDescriptor) ResultColumns {
+	return resultColumnsFromColDescs(tableID, len(colDescs), func(i int) *ColumnDescriptor {
+		return colDescs[i]
+	})
+}
+
+func resultColumnsFromColDescs(
+	tableID ID, numCols int, getColDesc func(int) *ColumnDescriptor,
+) ResultColumns {
+	cols := make(ResultColumns, numCols)
+	for i := range cols {
+		colDesc := getColDesc(i)
 		typ := colDesc.Type
 		if typ == nil {
 			panic(fmt.Sprintf("unsupported column type: %s", colDesc.Type.Family()))
 		}
-
-		hidden := colDesc.Hidden
-		cols = append(
-			cols,
-			ResultColumn{
-				Name:           colDesc.Name,
-				Typ:            typ,
-				Hidden:         hidden,
-				TableID:        tableID,
-				PGAttributeNum: colDesc.GetLogicalColumnID(),
-			},
-		)
+		cols[i] = ResultColumn{
+			Name:           colDesc.Name,
+			Typ:            typ,
+			Hidden:         colDesc.Hidden,
+			TableID:        tableID,
+			PGAttributeNum: colDesc.GetLogicalColumnID(),
+		}
 	}
 	return cols
 }