diff --git a/datastream-kafka-connector/src/test/java/com/linkedin/datastream/connectors/kafka/mirrormaker/TestKafkaMirrorMakerConnector.java b/datastream-kafka-connector/src/test/java/com/linkedin/datastream/connectors/kafka/mirrormaker/TestKafkaMirrorMakerConnector.java
index 19529aa79..08fc363fc 100644
--- a/datastream-kafka-connector/src/test/java/com/linkedin/datastream/connectors/kafka/mirrormaker/TestKafkaMirrorMakerConnector.java
+++ b/datastream-kafka-connector/src/test/java/com/linkedin/datastream/connectors/kafka/mirrormaker/TestKafkaMirrorMakerConnector.java
@@ -630,7 +630,7 @@ public void testFetchPartitionChange() throws Exception {
     Map<String, Optional<DatastreamGroupPartitionsMetadata>> partitionInfo = connector.getDatastreamPartitions();
     Assert.assertEquals(partitionInfo.get(group.getTaskPrefix()).get().getDatastreamGroup().getName(),
         group.getTaskPrefix());
-    Assert.assertEquals(new HashSet<>(partitionInfo.get(group.getTaskPrefix()).get().getPartitions()),
+    Assert.assertEquals(partitionInfo.get(group.getTaskPrefix()).get().getPartitions(),
         ImmutableSet.of(yummyTopic + "-0"));
 
     String saltyTopic = "SaltyPizza";
@@ -638,7 +638,7 @@ public void testFetchPartitionChange() throws Exception {
 
     Assert.assertTrue(PollUtils.poll(() -> partitionChangeCalls.get() == 2, POLL_PERIOD_MS, POLL_TIMEOUT_MS));
     partitionInfo = connector.getDatastreamPartitions();
-    Assert.assertEquals(new HashSet<>(partitionInfo.get(group.getTaskPrefix()).get().getPartitions()),
+    Assert.assertEquals(partitionInfo.get(group.getTaskPrefix()).get().getPartitions(),
         ImmutableSet.of(yummyTopic + "-0", saltyTopic + "-0", saltyTopic + "-1"));
     connector.stop();
   }
diff --git a/datastream-server-api/src/main/java/com/linkedin/datastream/server/DatastreamGroupPartitionsMetadata.java b/datastream-server-api/src/main/java/com/linkedin/datastream/server/DatastreamGroupPartitionsMetadata.java
index fa4503f88..5181e8d46 100644
--- a/datastream-server-api/src/main/java/com/linkedin/datastream/server/DatastreamGroupPartitionsMetadata.java
+++ b/datastream-server-api/src/main/java/com/linkedin/datastream/server/DatastreamGroupPartitionsMetadata.java
@@ -5,8 +5,11 @@
  */
 package com.linkedin.datastream.server;
 
+import java.util.ArrayList;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 
 import com.linkedin.datastream.common.LogUtils;
 
@@ -16,14 +19,23 @@
 public class DatastreamGroupPartitionsMetadata {
 
   private final DatastreamGroup _datastreamGroup;
-  private final List<String> _partitions;
+  private final Set<String> _partitions;
 
   /**
    * constructor
    * @param datastreamGroup datastream group which handle the partitions
-   * @param partitions the partitions that belong to this datastream
+   * @param partitions the partitions in a list that belong to this datastream
    */
   public DatastreamGroupPartitionsMetadata(DatastreamGroup datastreamGroup, List<String> partitions) {
+    this(datastreamGroup, new HashSet<>(partitions));
+  }
+
+  /**
+   * constructor
+   * @param datastreamGroup datastream group which handle the partitions
+   * @param partitions the partitions in a set that belong to this datastream
+   */
+  public DatastreamGroupPartitionsMetadata(DatastreamGroup datastreamGroup, Set<String> partitions) {
     _datastreamGroup = datastreamGroup;
     _partitions = partitions;
   }
@@ -32,12 +44,13 @@ public DatastreamGroup getDatastreamGroup() {
     return _datastreamGroup;
   }
 
-  public List<String> getPartitions() {
-    return Collections.unmodifiableList(_partitions);
+  public Set<String> getPartitions() {
+    return Collections.unmodifiableSet(_partitions);
   }
 
   @Override
   public String toString() {
-    return String.format("datastream %s, partitions %s", _datastreamGroup.getName(), LogUtils.logSummarizedTopicPartitionsMapping(_partitions));
+    return String.format("datastream %s, partitions %s", _datastreamGroup.getName(),
+        LogUtils.logSummarizedTopicPartitionsMapping(new ArrayList<>(_partitions)));
   }
 }
diff --git a/datastream-server/src/main/java/com/linkedin/datastream/server/assignment/LoadBasedPartitionAssigner.java b/datastream-server/src/main/java/com/linkedin/datastream/server/assignment/LoadBasedPartitionAssigner.java
index 35c2e1ef2..8feea662f 100644
--- a/datastream-server/src/main/java/com/linkedin/datastream/server/assignment/LoadBasedPartitionAssigner.java
+++ b/datastream-server/src/main/java/com/linkedin/datastream/server/assignment/LoadBasedPartitionAssigner.java
@@ -91,7 +91,7 @@ public Map<String, Set<DatastreamTask>> assignPartitions(
         tasks.forEach(task -> {
           if (task.getTaskPrefix().equals(datastreamGroupName)) {
             Set<String> retainedPartitions = new HashSet<>(task.getPartitionsV2());
-            retainedPartitions.retainAll(new HashSet<>(partitionMetadata.getPartitions()));
+            retainedPartitions.retainAll(partitionMetadata.getPartitions());
             newPartitionAssignmentMap.put(task.getId(), retainedPartitions);
             if (retainedPartitions.size() != task.getPartitionsV2().size()) {
               tasksWithChangedPartition.add(task.getId());
diff --git a/datastream-server/src/main/java/com/linkedin/datastream/server/assignment/StickyPartitionAssignmentStrategy.java b/datastream-server/src/main/java/com/linkedin/datastream/server/assignment/StickyPartitionAssignmentStrategy.java
index 8eb6d0dc7..4f3ae61c3 100644
--- a/datastream-server/src/main/java/com/linkedin/datastream/server/assignment/StickyPartitionAssignmentStrategy.java
+++ b/datastream-server/src/main/java/com/linkedin/datastream/server/assignment/StickyPartitionAssignmentStrategy.java
@@ -262,7 +262,7 @@ public Map<String, Set<DatastreamTask>> assignPartitions(Map<String,
           return task;
         } else {
           Set<String> newPartitions = new HashSet<>(task.getPartitionsV2());
-          newPartitions.retainAll(new HashSet<>(datastreamPartitions.getPartitions()));
+          newPartitions.retainAll(datastreamPartitions.getPartitions());
 
           //We need to create new task if the partition is changed
           boolean partitionChanged = newPartitions.size() != task.getPartitionsV2().size();
@@ -332,7 +332,7 @@ public Map<String, Set<DatastreamTask>> movePartitions(Map<String, Set<Datastrea
 
     Set<String> allToReassignPartitions = new HashSet<>();
     targetAssignment.values().forEach(allToReassignPartitions::addAll);
-    allToReassignPartitions.retainAll(new HashSet<>(partitionsMetadata.getPartitions()));
+    allToReassignPartitions.retainAll(partitionsMetadata.getPartitions());
 
     // construct a map to store the tasks and if it contain the partitions that can be released
     // map: <source taskName, partitions that need to be released>