Working end to end

gql/parser.go

@@ -152,7 +152,7 @@ func parseArguments(l *lex.Lexer) (result []pair, rerr error) {
 	for {
 		var p pair
 
-		// Get key.
+		// Get key
 		item := <-l.Items
 		if item.Typ == itemArgName {
 			p.Key = item.Val
@@ -164,7 +164,7 @@ func parseArguments(l *lex.Lexer) (result []pair, rerr error) {
 			return result, fmt.Errorf("Expecting argument name. Got: %v", item)
 		}
 
-		// Get value.
+		// Get value
 		item = <-l.Items
 		if item.Typ == itemArgVal {
 			p.Val = item.Val
@@ -238,7 +238,6 @@ func godeep(l *lex.Lexer, gq *GraphQuery) error {
 			return nil
 
 		} else if item.Typ == itemLeftRound {
-
 			args, err := parseArguments(l)
 			if err != nil {
 				return err

posting/list.go

@@ -720,15 +720,35 @@ func (l *List) LastCompactionTs() time.Time {
 	return l.lastCompact
 }
 
-func (l *List) GetUids() []uint64 {
+func (l *List) GetUids(offset, count int) []uint64 {
 	l.wg.Wait()
 	l.RLock()
 	defer l.RUnlock()
 
-	result := make([]uint64, l.length())
+	if offset < 0 {
+		glog.WithField("offset", offset).Fatal("Unexpected offset")
+		return make([]uint64, 0)
+	}
+
+	if count < 0 {
+		count = 0 - count
+		offset = l.length() - count
+	}
+
+	if count == 0 {
+		count = l.length() - offset
+
+	} else if count > l.length()-offset {
+		count = l.length() - offset
+	}
+	if count < 0 {
+		count = 0
+	}
+
+	result := make([]uint64, count)
 	result = result[:0]
 	var p types.Posting
-	for i := 0; i < l.length(); i++ {
+	for i := offset; i < count+offset && i < l.length(); i++ {
 		if ok := l.get(&p, i); !ok || p.Uid() == math.MaxUint64 {
 			break
 		}

posting/list_test.go

@@ -44,6 +44,32 @@ func checkUids(t *testing.T, l *List, uids ...uint64) error {
 			return fmt.Errorf("Expected: %v. Got: %v", uids[i], p.Uid())
 		}
 	}
+	if len(uids) >= 3 {
+		ruids := l.GetUids(1, 2)
+		if len(ruids) != 2 {
+			return fmt.Errorf("Expected result of length: 2. Got: %v", len(ruids))
+		}
+
+		for i := 0; i < len(ruids); i++ {
+			if ruids[i] != uids[1+i] {
+				return fmt.Errorf("GetUids expected: %v. Got: %v", uids[1+i], ruids[i])
+			}
+		}
+
+		ruids = l.GetUids(1, -2) // offset should be ignored.
+		ulen := len(uids)
+		if ulen > 2 && len(ruids) != 2 {
+			return fmt.Errorf("Expected result of length: 2. Got: %v", len(ruids))
+		}
+
+		for i := 0; i < len(ruids); i++ {
+			if ruids[i] != uids[ulen-2+i] {
+				return fmt.Errorf("GetUids neg count expected: %v. Got: %v",
+					uids[ulen-2+i], ruids[i])
+			}
+		}
+	}
+
 	return nil
 }
 

query/query.go

@@ -110,6 +110,8 @@ func (l *Latency) ToMap() map[string]string {
 // client convenient formats, like GraphQL / JSON.
 type SubGraph struct {
 	Attr     string
+	Count    int
+	Offset   int
 	Children []*SubGraph
 
 	query  []byte
@@ -325,9 +327,14 @@ func (g *SubGraph) PreTraverse() (gr *pb.GraphResponse, rerr error) {
 }
 
 func treeCopy(gq *gql.GraphQuery, sg *SubGraph) {
+	// Typically you act on the current node, and leave recursion to deal with
+	// children. But, in this case, we don't want to muck with the current
+	// node, because of the way we're dealing with the root node.
+	// So, we work on the children, and then recurse for grand children.
 	for _, gchild := range gq.Children {
 		dst := new(SubGraph)
 		dst.Attr = gchild.Attr
+		dst.Count = gchild.First
 		sg.Children = append(sg.Children, dst)
 		treeCopy(gchild, dst)
 	}
@@ -394,14 +401,14 @@ func newGraph(euid uint64, exid string) (*SubGraph, error) {
 	sg.Attr = "_root_"
 	sg.result = b.Bytes[b.Head():]
 	// Also add query for consistency and to allow for ToJson() later.
-	sg.query = createTaskQuery(sg.Attr, []uint64{euid})
+	sg.query = createTaskQuery(sg, []uint64{euid})
 	return sg, nil
 }
 
 // createTaskQuery generates the query buffer.
-func createTaskQuery(attr string, sorted []uint64) []byte {
+func createTaskQuery(sg *SubGraph, sorted []uint64) []byte {
 	b := flatbuffers.NewBuilder(0)
-	ao := b.CreateString(attr)
+	ao := b.CreateString(sg.Attr)
 
 	task.QueryStartUidsVector(b, len(sorted))
 	for i := len(sorted) - 1; i >= 0; i-- {
@@ -412,6 +419,8 @@ func createTaskQuery(attr string, sorted []uint64) []byte {
 	task.QueryStart(b)
 	task.QueryAddAttr(b, ao)
 	task.QueryAddUids(b, vend)
+	task.QueryAddCount(b, int32(sg.Count))
+
 	qend := task.QueryEnd(b)
 	b.Finish(qend)
 	return b.Bytes[b.Head():]
@@ -531,7 +540,7 @@ func ProcessGraph(sg *SubGraph, rch chan error, td time.Duration) {
 	childchan := make(chan error, len(sg.Children))
 	for i := 0; i < len(sg.Children); i++ {
 		child := sg.Children[i]
-		child.query = createTaskQuery(child.Attr, sorted)
+		child.query = createTaskQuery(child, sorted)
 		go ProcessGraph(child, childchan, timeleft)
 	}
 

task.fbs

@@ -3,6 +3,8 @@ namespace task;
 table Query {
 	attr:string;
 	uids:[ulong];
+	count:int;
+	offset:int;
 }
 
 table Value {

task/Query.go

@@ -39,9 +39,27 @@ func (rcv *Query) UidsLength() int {
 	return 0
 }
 
-func QueryStart(builder *flatbuffers.Builder) { builder.StartObject(2) }
+func (rcv *Query) Count() int32 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(8))
+	if o != 0 {
+		return rcv._tab.GetInt32(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func (rcv *Query) Offset() int32 {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(10))
+	if o != 0 {
+		return rcv._tab.GetInt32(o + rcv._tab.Pos)
+	}
+	return 0
+}
+
+func QueryStart(builder *flatbuffers.Builder) { builder.StartObject(4) }
 func QueryAddAttr(builder *flatbuffers.Builder, attr flatbuffers.UOffsetT) { builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(attr), 0) }
 func QueryAddUids(builder *flatbuffers.Builder, uids flatbuffers.UOffsetT) { builder.PrependUOffsetTSlot(1, flatbuffers.UOffsetT(uids), 0) }
 func QueryStartUidsVector(builder *flatbuffers.Builder, numElems int) flatbuffers.UOffsetT { return builder.StartVector(8, numElems, 8)
 }
+func QueryAddCount(builder *flatbuffers.Builder, count int32) { builder.PrependInt32Slot(2, count, 0) }
+func QueryAddOffset(builder *flatbuffers.Builder, offset int32) { builder.PrependInt32Slot(3, offset, 0) }
 func QueryEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT { return builder.EndObject() }

worker/task.go

@@ -94,7 +94,7 @@ func processTask(query []byte) (result []byte, rerr error) {
 		task.ValueAddVal(b, valoffset)
 		voffsets[i] = task.ValueEnd(b)
 
-		ulist := pl.GetUids()
+		ulist := pl.GetUids(int(q.Offset()), int(q.Count()))
 		uoffsets[i] = x.UidlistOffset(b, ulist)
 	}
 	task.ResultStartValuesVector(b, len(voffsets))