add sorting for ints/mutex in batch importer

fixes pathological case where imports with randomly ordered IDs which
spanned multiple shards and included ints or mutex fields could be
incredibly slow due to making 1000s of requests.

client/batch.go

@@ -2,6 +2,7 @@
 package client
 
 import (
+	"sort"
 	"sync"
 	"time"
 
@@ -20,7 +21,9 @@ const (
 // order. Could be worth sorting everything after translation (as an
 // option?). Instead of sorting all simultaneously, it might be faster
 // (more cache friendly) to sort ids and save the swap ops to apply to
-// everything else that needs to be sorted.
+// everything else that needs to be sorted. Note: we're already doing
+// some sorting in importValueData and importMutexData, so if we
+// implement it at the top level, remember to remove it there.
 
 // TODO support clearing values? nil values in records are ignored,
 // but perhaps we could have a special type indicating that a bit or
@@ -1216,6 +1219,22 @@ func (b *Batch) makeFragments(frags, clearFrags fragments) (fragments, fragments
 	return frags, clearFrags, nil
 }
 
+type valsByIDsSortable struct {
+	ids  []uint64
+	vals []int64
+	// shard width so we can compare by shard instead of ID
+	width uint64
+}
+
+func (v *valsByIDsSortable) Len() int { return len(v.ids) }
+
+// comparing on shard rather than ID was twice as fast in informal tests
+func (v *valsByIDsSortable) Less(i, j int) bool { return v.ids[i]/v.width < v.ids[j]/v.width }
+func (v *valsByIDsSortable) Swap(i, j int) {
+	v.ids[i], v.ids[j] = v.ids[j], v.ids[i]
+	v.vals[i], v.vals[j] = v.vals[j], v.vals[i]
+}
+
 // importValueData imports data for int fields.
 func (b *Batch) importValueData() error {
 	shardWidth := b.index.ShardWidth()
@@ -1246,6 +1265,12 @@ func (b *Batch) importValueData() error {
 		if len(ids) == 0 {
 			continue // TODO test this "all nil" case
 		}
+
+		sc := &valsByIDsSortable{ids: ids, vals: bvalues, width: shardWidth}
+		if !sort.IsSorted(sc) {
+			sort.Sort(sc)
+		}
+
 		curShard := ids[0] / shardWidth
 		startIdx := 0
 		for i := 1; i <= len(ids); i++ {
@@ -1285,6 +1310,22 @@ func (b *Batch) importValueData() error {
 	return errors.Wrap(err, "importing value data")
 }
 
+type rowsByIDsSortable struct {
+	ids  []uint64
+	rows []uint64
+	// shard width so we can compare by shard instead of ID
+	width uint64
+}
+
+func (v *rowsByIDsSortable) Len() int { return len(v.ids) }
+
+// comparing on shard rather than ID was twice as fast in informal tests
+func (v *rowsByIDsSortable) Less(i, j int) bool { return v.ids[i]/v.width < v.ids[j]/v.width }
+func (v *rowsByIDsSortable) Swap(i, j int) {
+	v.ids[i], v.ids[j] = v.ids[j], v.ids[i]
+	v.rows[i], v.rows[j] = v.rows[j], v.rows[i]
+}
+
 // TODO this should work for bools as well - just need to support them
 // at batch creation time and when calling Add, I think.
 func (b *Batch) importMutexData() error {
@@ -1319,6 +1360,12 @@ func (b *Batch) importMutexData() error {
 		if len(ids) == 0 {
 			continue
 		}
+
+		sc := &rowsByIDsSortable{ids: ids, rows: rowIDs, width: shardWidth}
+		if !sort.IsSorted(sc) {
+			sort.Sort(sc)
+		}
+
 		curShard := ids[0] / shardWidth
 		startIdx := 0
 		for i := 1; i <= len(ids); i++ {