Add AdaptiveRangeLimit constant for adaptive range limits

pager.go

@@ -32,7 +32,7 @@ type pager struct {
 }
 
 func addLimitTokenString(w io.Writer, limit int, token string) {
-	if limit > 0 {
+	if limit == AdaptiveRangeLimit || limit > 0 {
 		fmt.Fprintf(w, " limit %d", limit)
 	}
 	if token != "" {

range.go

@@ -30,6 +30,14 @@ import (
 	"github.com/pkg/errors"
 )
 
+const (
+	// AdaptiveRangeLimit is a sentinel value that is used to indicate an intent
+	// to range over data in a partition as fast as possible. The server will
+	// determine an appropriate limit to use to range over the partition as fast
+	// as possible while ensuring the server remains healthy.
+	AdaptiveRangeLimit = -1
+)
+
 // RangeOp is used to specify constraints to Range calls
 type RangeOp struct {
 	pager

range_test.go

@@ -69,6 +69,12 @@ var rangeTestCases = []struct {
 		stringer:  "<empty> limit 10",
 		converted: "<empty> limit 10",
 	},
+	{
+		descript:  "empty with adaptive limit",
+		rop:       NewRangeOp(&AllTypes{}).Limit(AdaptiveRangeLimit),
+		stringer:  "<empty> limit -1",
+		converted: "<empty> limit -1",
+	},
 	{
 		descript:  "empty with token",
 		rop:       NewRangeOp(&AllTypes{}).Offset("toketoketoke"),