FIX: Send flush op to master node only.

src/main/java/net/spy/memcached/ArcusClient.java

@@ -1902,7 +1902,8 @@ public OperationFuture<Boolean> flush(final String prefix) {
 
   @Override
   public OperationFuture<Boolean> flush(final String prefix, final int delay) {
-    Collection<MemcachedNode> nodes = getAllNodes();
+    Collection<MemcachedNode> nodes = getFlushNodes();
+
     final BroadcastFuture<Boolean> rv
             = new BroadcastFuture<>(operationTimeout, Boolean.TRUE, nodes.size());
     final Map<MemcachedNode, Operation> opsMap = new HashMap<>();

src/main/java/net/spy/memcached/ArcusReplKetamaNodeLocator.java

@@ -32,6 +32,7 @@
 import java.util.SortedSet;
 import java.util.TreeMap;
 import java.util.TreeSet;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 
@@ -41,7 +42,7 @@
 public final class ArcusReplKetamaNodeLocator extends SpyObject implements NodeLocator {
 
   private final TreeMap<Long, SortedSet<MemcachedReplicaGroup>> ketamaGroups;
-  private final HashMap<String, MemcachedReplicaGroup> allGroups;
+  private final ConcurrentHashMap<String, MemcachedReplicaGroup> allGroups;
   private final Collection<MemcachedNode> allNodes;
 
   /* ENABLE_MIGRATION if */
@@ -67,7 +68,7 @@ public ArcusReplKetamaNodeLocator(List<MemcachedNode> nodes) {
     super();
     allNodes = nodes;
     ketamaGroups = new TreeMap<>();
-    allGroups = new HashMap<>();
+    allGroups = new ConcurrentHashMap<>();
 
     // create all memcached replica group
     for (MemcachedNode node : nodes) {
@@ -103,7 +104,7 @@ public ArcusReplKetamaNodeLocator(List<MemcachedNode> nodes) {
   }
 
   private ArcusReplKetamaNodeLocator(TreeMap<Long, SortedSet<MemcachedReplicaGroup>> kg,
-                                     HashMap<String, MemcachedReplicaGroup> ag,
+                                     ConcurrentHashMap<String, MemcachedReplicaGroup> ag,
                                      Collection<MemcachedNode> an) {
     super();
     ketamaGroups = kg;
@@ -208,7 +209,8 @@ public NodeLocator getReadonlyCopy() {
     lock.lock();
     try {
       TreeMap<Long, SortedSet<MemcachedReplicaGroup>> ketamaCopy = new TreeMap<>();
-      HashMap<String, MemcachedReplicaGroup> groupsCopy = new HashMap<>(allGroups.size());
+      ConcurrentHashMap<String, MemcachedReplicaGroup> groupsCopy
+              = new ConcurrentHashMap<>(allGroups.size());
       Collection<MemcachedNode> nodesCopy = new ArrayList<>(allNodes.size());
 
       // Rewrite the values a copy of the map

src/main/java/net/spy/memcached/MemcachedClient.java

@@ -39,6 +39,7 @@
 import java.util.concurrent.Future;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
+import java.util.stream.Collectors;
 
 import net.spy.memcached.auth.AuthDescriptor;
 import net.spy.memcached.auth.AuthThreadMonitor;
@@ -1880,7 +1881,8 @@ public void complete() {
    *                               is too full to accept any more requests
    */
   public Future<Boolean> flush(final int delay) {
-    Collection<MemcachedNode> nodes = getAllNodes();
+    Collection<MemcachedNode> nodes = getFlushNodes();
+
     final BroadcastFuture<Boolean> rv
             = new BroadcastFuture<>(operationTimeout, Boolean.TRUE, nodes.size());
     final Map<MemcachedNode, Operation> opsMap = new HashMap<>();
@@ -2148,6 +2150,18 @@ protected Collection<MemcachedNode> getAllNodes() {
     return conn.getLocator().getAll();
   }
 
+  protected Collection<MemcachedNode> getFlushNodes() {
+    /* ENABLE_REPLICATION if */
+    if (conn.getArcusReplEnabled()) {
+      return ((ArcusReplKetamaNodeLocator) getNodeLocator()).getAllGroups().values()
+              .stream()
+              .map(MemcachedReplicaGroup::getMasterNode)
+              .collect(Collectors.toList());
+    }
+    /* ENABLE_REPLICATION end */
+    return conn.getLocator().getAll();
+  }
+
   /**
    * Turn the list of keys into groups of keys.
    * All keys in a group belong to the same memcached server.