diff --git a/cluster.go b/cluster.go
index 4565e91f3..5c5c0e7f1 100644
--- a/cluster.go
+++ b/cluster.go
@@ -184,6 +184,7 @@ type cluster struct { // nolint: maligned
 	ReplicaN int
 
 	// Threshold for logging long-running queries
+	// TODO(2.0) move this out of cluster. (why is it here??)
 	longQueryTime time.Duration
 
 	// Maximum number of Set() or Clear() commands per request.
diff --git a/fragment.go b/fragment.go
index 067814a0b..c09461470 100644
--- a/fragment.go
+++ b/fragment.go
@@ -1732,8 +1732,10 @@ func (f *fragment) importRoaring(data []byte, clear bool) error {
 	rowSet := make([]uint64, 0)
 	var lastRow uint64 = math.MaxUint64
 
+	incomingCnt := 0
 	for iter.Next() {
-		key, _ := iter.Value()
+		key, c := iter.Value()
+		incomingCnt += int(c.N())
 
 		// virtual row for the current container
 		vRow := key >> shardVsContainerExponent
@@ -1749,8 +1751,13 @@ func (f *fragment) importRoaring(data []byte, clear bool) error {
 	if clear {
 		bm = f.storage.Difference(bm)
 	} else {
-		if f.storage.Count() > 0 {
-			bm = f.storage.Union(bm)
+		if cnt := f.storage.Count(); cnt > 0 {
+			if incomingCnt > int(cnt) {
+				bm.UnionInPlace(f.storage)
+			} else {
+				f.storage.UnionInPlace(bm)
+				bm = f.storage
+			}
 		}
 	}
 
diff --git a/server/config.go b/server/config.go
index 6223f07da..9c787f92e 100644
--- a/server/config.go
+++ b/server/config.go
@@ -75,10 +75,11 @@ type Config struct {
 
 	Cluster struct {
 		// Disabled controls whether clustering functionality is enabled.
-		Disabled      bool          `toml:"disabled"`
-		Coordinator   bool          `toml:"coordinator"`
-		ReplicaN      int           `toml:"replicas"`
-		Hosts         []string      `toml:"hosts"`
+		Disabled    bool     `toml:"disabled"`
+		Coordinator bool     `toml:"coordinator"`
+		ReplicaN    int      `toml:"replicas"`
+		Hosts       []string `toml:"hosts"`
+		// TODO(2.0) move this out of cluster. (why is it here??)
 		LongQueryTime toml.Duration `toml:"long-query-time"`
 	} `toml:"cluster"`