Use a different stream writer id for split keys.

dgraph/cmd/bulk/reduce.go

@@ -77,9 +77,7 @@ func (r *reducer) run() error {
 			}
 
 			writer := db.NewStreamWriter()
-			if err := writer.Prepare(); err != nil {
-				x.Check(err)
-			}
+			x.Check(writer.Prepare())
 
 			ci := &countIndexer{reducer: r, writer: writer}
 			sort.Slice(partitionKeys, func(i, j int) bool {
@@ -93,9 +91,7 @@ func (r *reducer) run() error {
 			r.reduce(partitionKeys, mapItrs, ci)
 			ci.wait()
 
-			if err := writer.Flush(); err != nil {
-				x.Check(err)
-			}
+			x.Check(writer.Flush())
 			for _, itr := range mapItrs {
 				if err := itr.Close(); err != nil {
 					fmt.Printf("Error while closing iterator: %v", err)
@@ -316,6 +312,9 @@ func (r *reducer) encode(entryCh chan *encodeRequest, closer *y.Closer) {
 			x.Check(err)
 			x.AssertTrue(len(pk.Attr) > 0)
 			kv.StreamId = r.streamIdFor(pk.Attr)
+			if pk.HasStartUid {
+				kv.StreamId |= 0x80000000
+			}
 		}
 		req.countKeys = countKeys
 		req.wg.Done()
@@ -475,15 +474,23 @@ func (r *reducer) toList(bufEntries [][]byte, list *bpb.KVList) []*countIndexEnt
 		}
 
 		pl.Pack = codec.Encode(uids, 256)
-		val, err := pl.Marshal()
-		x.Check(err)
-		kv := &bpb.KV{
-			Key:      y.Copy(currentKey),
-			Value:    val,
-			UserMeta: userMeta,
-			Version:  writeVersionTs,
+		shouldSplit := pl.Size() > (1<<20)/2 && len(pl.Pack.Blocks) > 1
+		if shouldSplit {
+			l := posting.NewList(y.Copy(currentKey), pl, writeVersionTs)
+			kvs, err := l.Rollup()
+			x.Check(err)
+			list.Kv = append(list.Kv, kvs...)
+		} else {
+			val, err := pl.Marshal()
+			x.Check(err)
+			kv := &bpb.KV{
+				Key:      y.Copy(currentKey),
+				Value:    val,
+				UserMeta: userMeta,
+				Version:  writeVersionTs,
+			}
+			list.Kv = append(list.Kv, kv)
 		}
-		list.Kv = append(list.Kv, kv)
 
 		uids = uids[:0]
 		pl.Reset()

posting/list.go

@@ -798,6 +798,12 @@ func (l *List) Rollup() ([]*bpb.KV, error) {
 		kvs = append(kvs, kv)
 	}
 
+	// Sort the KVs by their key so that the main part of the list is at the
+	// start of the list and all other parts appear in the order of their start UID.
+	sort.Slice(kvs, func(i, j int) bool {
+		return bytes.Compare(kvs[i].Key, kvs[j].Key) <= 0
+	})
+
 	return kvs, nil
 }