feat(query): Parallelize field iterator planning

query/select.go

@@ -6,11 +6,13 @@ import (
 	"io"
 	"sort"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/influxdata/influxdb/pkg/tracing"
 	"github.com/influxdata/influxdb/query/internal/gota"
 	"github.com/influxdata/influxql"
+	"golang.org/x/sync/errgroup"
 )
 
 var DefaultTypeMapper = influxql.MultiTypeMapper(
@@ -726,28 +728,44 @@ func buildCursor(ctx context.Context, stmt *influxql.SelectStatement, ic Iterato
 
 	// Produce an iterator for every single call and create an iterator scanner
 	// associated with it.
+	var g errgroup.Group
+	var mu sync.Mutex
 	scanners := make([]IteratorScanner, 0, len(valueMapper.calls))
 	for call := range valueMapper.calls {
+		call := call
+
 		driver := valueMapper.table[call]
 		if driver.Type == influxql.Unknown {
 			// The primary driver of this call is of unknown type, so skip this.
 			continue
 		}
 
-		itr, err := buildFieldIterator(ctx, call, ic, stmt.Sources, opt, selector, stmt.Target != nil)
-		if err != nil {
-			for _, s := range scanners {
-				s.Close()
+		g.Go(func() error {
+			itr, err := buildFieldIterator(ctx, call, ic, stmt.Sources, opt, selector, stmt.Target != nil)
+			if err != nil {
+				return err
 			}
-			return nil, err
+
+			keys := make([]influxql.VarRef, 0, len(auxKeys)+1)
+			keys = append(keys, driver)
+			keys = append(keys, auxKeys...)
+
+			scanner := NewIteratorScanner(itr, keys, opt.FillValue)
+
+			mu.Lock()
+			scanners = append(scanners, scanner)
+			mu.Unlock()
+
+			return nil
+		})
+	}
+
+	// Close all scanners if any iterator fails.
+	if err := g.Wait(); err != nil {
+		for _, s := range scanners {
+			s.Close()
 		}
-
-		keys := make([]influxql.VarRef, 0, len(auxKeys)+1)
-		keys = append(keys, driver)
-		keys = append(keys, auxKeys...)
-
-		scanner := NewIteratorScanner(itr, keys, opt.FillValue)
-		scanners = append(scanners, scanner)
+		return nil, err
 	}
 
 	if len(scanners) == 0 {