datastore: query cache

swift.go

@@ -20,11 +20,13 @@ type SwiftContainer struct {
 }
 
 type QueryCache struct {
-	index int
-	name  string
+	prefix string
+	index  int
+	name   string
 }
 
 func (c *QueryCache) Invalidate() {
+	c.prefix = ""
 	c.name = ""
 }
 
@@ -124,12 +126,12 @@ func (s *SwiftContainer) Query(q dsq.Query) (dsq.Results, error) {
 
 	offset := q.Offset
 
-	if s.cache.name != "" && s.cache.index <= offset {
+	if s.cache.prefix == opts.Prefix && s.cache.name != "" && s.cache.index <= offset {
 		opts.Marker = s.cache.name
 		offset = s.cache.index - offset
 	}
 
-	end := q.Offset + q.Limit
+	end := offset + q.Limit
 	if end != 0 && end < opts.Limit {
 		opts.Limit = end
 	}
@@ -149,10 +151,6 @@ func (s *SwiftContainer) Query(q dsq.Query) (dsq.Results, error) {
 			}
 
 			if len(names) == 0 {
-				if q.Limit > count && (q.Limit-count) < opts.Limit {
-					opts.Limit = q.Limit - count
-				}
-
 				for len(names) == 0 || offset > 0 {
 					if doneFetching {
 						return dsq.Result{}, false
@@ -192,9 +190,17 @@ func (s *SwiftContainer) Query(q dsq.Query) (dsq.Results, error) {
 			name := names[0]
 			names = names[1:]
 
+			if len(names) == 0 && q.Limit > count && (q.Limit-count) < opts.Limit {
+				opts.Limit = q.Limit - count
+			}
+
+			// Cache the last item
 			if q.Limit != 0 && count == q.Limit {
-				s.cache.index = q.Offset + count
-				s.cache.name = name
+				s.cache = QueryCache{
+					prefix: opts.Prefix,
+					index:  q.Offset + count,
+					name:   name,
+				}
 			}
 
 			key := "/" + name

swift_test.go

@@ -125,6 +125,27 @@ func TestQuery(t *testing.T) {
 		"/a/b/d",
 		"/a/c",
 	}, rs)
+
+	rs, err = d.Query(dsq.Query{Prefix: "/a/", Offset: 4, Limit: 1})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	expectMatches(t, []string{
+		"/a/d",
+	}, rs)
+
+	rs, err = d.Query(dsq.Query{Prefix: "/a/", Offset: 1})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	expectMatches(t, []string{
+		"/a/b/c",
+		"/a/b/d",
+		"/a/c",
+		"/a/d",
+	}, rs)
 }
 
 func TestHas(t *testing.T) {