Make gathering multimap stats not to break last access merge policy

Gathering multimap statistics calls
MultiMapPartitionContainer#getMultiMapContainer() that updates the
lastAccessTime of the returned container, which in the end breaks the
last access merge policy. This is fixed by making gathering statistics
not to count an access. Also, retrieving the container on backups
for the given partition made not to be considered an access.

Fixes hazelcast#16001

hazelcast/src/main/java/com/hazelcast/multimap/impl/MultiMapPartitionContainer.java

@@ -61,9 +61,20 @@ public MultiMapContainer getOrCreateMultiMapContainer(String name, boolean isAcc
         return container;
     }
 
-    public MultiMapContainer getMultiMapContainer(String name) {
+    /**
+     * Returns the {@link MultiMapContainer} with the given {@code name}
+     * if exists or {@code null otherwise}. Depending on the {@code isAccess}
+     * parameter this call updates the {@code lastAccessTime} field of the
+     * container.
+     *
+     * @param name     The name of the container to retrieve
+     * @param isAccess Indicates whether or not this call should be treated
+     *                 as an access
+     * @return the container or {@code null} if doesn't exist
+     */
+    public MultiMapContainer getMultiMapContainer(String name, boolean isAccess) {
         MultiMapContainer container = containerMap.get(name);
-        if (container != null) {
+        if (container != null && isAccess) {
             container.access();
         }
         return container;

hazelcast/src/main/java/com/hazelcast/multimap/impl/MultiMapService.java

@@ -212,12 +212,14 @@ public Set<Data> localKeySet(String name) {
         Set<Data> keySet = new HashSet<Data>();
         for (int i = 0; i < nodeEngine.getPartitionService().getPartitionCount(); i++) {
             IPartition partition = nodeEngine.getPartitionService().getPartition(i);
+            boolean isLocalPartition = partition.isLocal();
             MultiMapPartitionContainer partitionContainer = getPartitionContainer(i);
-            MultiMapContainer multiMapContainer = partitionContainer.getMultiMapContainer(name);
+            // we should not treat retrieving the container on backups an access
+            MultiMapContainer multiMapContainer = partitionContainer.getMultiMapContainer(name, isLocalPartition);
             if (multiMapContainer == null) {
                 continue;
             }
-            if (partition.isLocal()) {
+            if (isLocalPartition) {
                 keySet.addAll(multiMapContainer.keySet());
             }
         }
@@ -394,7 +396,7 @@ public LocalMultiMapStats createStats(String name) {
         for (int partitionId = 0; partitionId < nodeEngine.getPartitionService().getPartitionCount(); partitionId++) {
             IPartition partition = nodeEngine.getPartitionService().getPartition(partitionId, false);
             MultiMapPartitionContainer partitionContainer = getPartitionContainer(partitionId);
-            MultiMapContainer multiMapContainer = partitionContainer.getMultiMapContainer(name);
+            MultiMapContainer multiMapContainer = partitionContainer.getMultiMapContainer(name, false);
             if (multiMapContainer == null) {
                 continue;
             }

hazelcast/src/test/java/com/hazelcast/multimap/MultiMapSplitBrainTest.java

@@ -45,6 +45,10 @@
 import java.util.Collection;
 import java.util.Map;
 
+import static com.hazelcast.internal.diagnostics.Diagnostics.ENABLED;
+import static com.hazelcast.internal.diagnostics.Diagnostics.METRICS_DISTRIBUTED_DATASTRUCTURES;
+import static com.hazelcast.internal.diagnostics.Diagnostics.METRICS_LEVEL;
+import static com.hazelcast.internal.metrics.ProbeLevel.INFO;
 import static com.hazelcast.multimap.MultiMapTestUtil.getBackupMultiMap;
 import static java.util.Arrays.asList;
 import static org.junit.Assert.assertFalse;
@@ -128,6 +132,11 @@ protected Config config() {
                 .setStatisticsEnabled(true)
                 .setBackupCount(1)
                 .setAsyncBackupCount(0);
+
+        config.getProperties().setProperty(ENABLED.getName(), "true");
+        config.getProperties().setProperty(METRICS_DISTRIBUTED_DATASTRUCTURES.getName(), "true");
+        config.getProperties().setProperty(METRICS_LEVEL.getName(), INFO.name());
+
         return config;
     }
 

hazelcast/src/test/java/com/hazelcast/multimap/MultiMapTestUtil.java

@@ -63,7 +63,7 @@ public static <K, V> Map<K, Collection<V>> getBackupMultiMap(HazelcastInstance[]
                     continue;
                 }
                 MultiMapPartitionContainer partitionContainer = mapService.getPartitionContainer(partitionId);
-                MultiMapContainer multiMapContainer = partitionContainer.getMultiMapContainer(multiMapName);
+                MultiMapContainer multiMapContainer = partitionContainer.getMultiMapContainer(multiMapName, false);
                 if (multiMapContainer == null) {
                     continue;
                 }

hazelcast/src/test/java/com/hazelcast/test/starter/answer/test/AnswerTest.java

@@ -423,7 +423,7 @@ public void testMultiMapService() {
         multiMap.put(key, "value2");
 
         MultiMapPartitionContainer partitionContainer = multiMapService.getPartitionContainer(partitionId);
-        MultiMapContainer multiMapContainer = partitionContainer.getMultiMapContainer("myMultiMap");
+        MultiMapContainer multiMapContainer = partitionContainer.getMultiMapContainer("myMultiMap", false);
 
         ConcurrentMap<Data, MultiMapValue> multiMapValues = multiMapContainer.getMultiMapValues();
         for (Map.Entry<Data, MultiMapValue> entry : multiMapValues.entrySet()) {