master: ensure only one exclusive vacuum process

fix https://github.com/chrislusf/seaweedfs/issues/1011

weed/topology/topology.go

@@ -16,6 +16,7 @@ import (
 )
 
 type Topology struct {
+	vacuumLockCounter int64
 	NodeImpl
 
 	collectionMap  *util.ConcurrentReadMap
@@ -33,6 +34,7 @@ type Topology struct {
 	Configuration *Configuration
 
 	RaftServer raft.Server
+
 }
 
 func NewTopology(id string, seq sequence.Sequencer, volumeSizeLimit uint64, pulse int) *Topology {

weed/topology/topology_vacuum.go

@@ -2,6 +2,7 @@ package topology
 
 import (
 	"context"
+	"sync/atomic"
 	"time"
 
 	"github.com/chrislusf/seaweedfs/weed/storage/needle"
@@ -121,6 +122,16 @@ func batchVacuumVolumeCleanup(grpcDialOption grpc.DialOption, vl *VolumeLayout,
 }
 
 func (t *Topology) Vacuum(grpcDialOption grpc.DialOption, garbageThreshold float64, preallocate int64) int {
+
+	// if there is vacuum going on, return immediately
+	swapped := atomic.CompareAndSwapInt64(&t.vacuumLockCounter, 0, 1)
+	if !swapped {
+		return 0
+	}
+	defer atomic.StoreInt64(&t.vacuumLockCounter, 0)
+
+	// now only one vacuum process going on
+
 	glog.V(1).Infof("Start vacuum on demand with threshold: %f", garbageThreshold)
 	for _, col := range t.collectionMap.Items() {
 		c := col.(*Collection)