Fix a bug due to which we were unable to retrieve xids.

query/query.go

@@ -403,7 +403,6 @@ func sortedUniqueUids(r *task.Result) (sorted []uint64, rerr error) {
 func ProcessGraph(sg *SubGraph, rch chan error) {
 	var err error
 	if len(sg.query) > 0 && sg.Attr != "_root_" {
-		// This task execution would go over the wire in later versions.
 		sg.result, err = worker.ProcessTaskOverNetwork(sg.query)
 		if err != nil {
 			x.Err(glog, err).Error("While processing task.")
@@ -416,6 +415,14 @@ func ProcessGraph(sg *SubGraph, rch chan error) {
 	r := new(task.Result)
 	r.Init(sg.result, uo)
 
+	if r.ValuesLength() > 0 {
+		var v task.Value
+		if r.Values(&v, 0) {
+			glog.WithField("attr", sg.Attr).WithField("val", string(v.ValBytes())).
+				Info("Sample value")
+		}
+	}
+
 	sorted, err := sortedUniqueUids(r)
 	if err != nil {
 		x.Err(glog, err).Error("While processing task.")

tools/dlist/main.go

@@ -101,5 +101,8 @@ func main() {
 	if err != nil {
 		glog.WithError(err).Fatal("Unable to get key")
 	}
+	if len(val) == 0 {
+		glog.Fatal("Unable to find posting list")
+	}
 	output(val)
 }

worker/task.go

@@ -51,7 +51,12 @@ func processTask(query []byte) (result []byte, rerr error) {
 	uo := flatbuffers.GetUOffsetT(query)
 	q := new(task.Query)
 	q.Init(query, uo)
+
 	attr := string(q.Attr())
+	store := dataStore
+	if attr == "_xid_" {
+		store = uidStore
+	}
 
 	b := flatbuffers.NewBuilder(0)
 	voffsets := make([]flatbuffers.UOffsetT, q.UidsLength())
@@ -60,7 +65,7 @@ func processTask(query []byte) (result []byte, rerr error) {
 	for i := 0; i < q.UidsLength(); i++ {
 		uid := q.Uids(i)
 		key := posting.Key(uid, attr)
-		pl := posting.GetOrCreate(key, dataStore)
+		pl := posting.GetOrCreate(key, store)
 
 		var valoffset flatbuffers.UOffsetT
 		if val, err := pl.Value(); err != nil {

worker/worker.go

@@ -126,9 +126,10 @@ func (w *Worker) ServeTask(query *conn.Query, reply *conn.Reply) (rerr error) {
 	q := new(task.Query)
 	q.Init(query.Data, uo)
 	attr := string(q.Attr())
-	glog.WithField("attr", attr).WithField("instanceIdx", instanceIdx).Info("ServeTask")
+	glog.WithField("attr", attr).WithField("num_uids", q.UidsLength()).
+		WithField("instanceIdx", instanceIdx).Info("ServeTask")
 
-	if attr == "_xid_" ||
+	if (instanceIdx == 0 && attr == "_xid_") ||
 		farm.Fingerprint64([]byte(attr))%numInstances == instanceIdx {
 
 		reply.Data, rerr = processTask(query.Data)