Remove unnecessary refresh listeners from NRTReplicationReaderManager.

server/src/internalClusterTest/java/org/opensearch/indices/replication/SegmentReplicationRelocationIT.java

@@ -60,7 +60,7 @@ public void testPrimaryRelocation() throws Exception {
         createIndex(1);
         final String replica = internalCluster().startNode();
         ensureGreen(INDEX_NAME);
-        final int initialDocCount = scaledRandomIntBetween(100, 1000);
+        final int initialDocCount = scaledRandomIntBetween(10, 100);
         final WriteRequest.RefreshPolicy refreshPolicy = randomFrom(WriteRequest.RefreshPolicy.values());
         final List<ActionFuture<IndexResponse>> pendingIndexResponses = new ArrayList<>();
         for (int i = 0; i < initialDocCount; i++) {
@@ -137,7 +137,7 @@ public void testPrimaryRelocationWithSegRepFailure() throws Exception {
         createIndex(1);
         final String replica = internalCluster().startNode();
         ensureGreen(INDEX_NAME);
-        final int initialDocCount = scaledRandomIntBetween(100, 1000);
+        final int initialDocCount = scaledRandomIntBetween(10, 100);
         final WriteRequest.RefreshPolicy refreshPolicy = randomFrom(WriteRequest.RefreshPolicy.values());
         final List<ActionFuture<IndexResponse>> pendingIndexResponses = new ArrayList<>();
         for (int i = 0; i < initialDocCount; i++) {

server/src/main/java/org/opensearch/index/engine/NRTReplicationEngine.java

@@ -77,9 +77,10 @@ public NRTReplicationEngine(EngineConfig engineConfig) {
             this.completionStatsCache = new CompletionStatsCache(() -> acquireSearcher("completion_stats"));
             this.readerManager = readerManager;
             this.readerManager.addListener(completionStatsCache);
-            for (ReferenceManager.RefreshListener listener : engineConfig.getExternalRefreshListener()) {
-                this.readerManager.addListener(listener);
-            }
+            // NRT Replicas do not have a concept of Internal vs External reader managers.
+            // We also do not want to wire up refresh listeners for waitFor & pending refresh location.
+            // which are the current external listeners set from IndexShard.
+            // Only wire up the internal listeners.
             for (ReferenceManager.RefreshListener listener : engineConfig.getInternalRefreshListener()) {
                 this.readerManager.addListener(listener);
             }
@@ -322,22 +323,12 @@ public List<Segment> segments(boolean verbose) {
 
     @Override
     public void refresh(String source) throws EngineException {
-        maybeRefresh(source);
+        // Refresh on this engine should only ever happen in the reader after new segments arrive.
     }
 
     @Override
     public boolean maybeRefresh(String source) throws EngineException {
-        ensureOpen();
-        try {
-            return readerManager.maybeRefresh();
-        } catch (IOException e) {
-            try {
-                failEngine("refresh failed source[" + source + "]", e);
-            } catch (Exception inner) {
-                e.addSuppressed(inner);
-            }
-            throw new RefreshFailedEngineException(shardId, e);
-        }
+        return false;
     }
 
     @Override

server/src/main/java/org/opensearch/index/engine/NRTReplicationReaderManager.java

@@ -103,7 +103,7 @@ public void updateSegments(SegmentInfos infos) throws IOException {
         // is always increased.
         infos.updateGeneration(currentInfos);
         currentInfos = infos;
-        maybeRefreshBlocking();
+        maybeRefresh();
     }
 
     public SegmentInfos getSegmentInfos() {

server/src/main/java/org/opensearch/index/shard/IndexShard.java

@@ -4423,7 +4423,8 @@ public void addRefreshListener(Translog.Location location, Consumer<Boolean> lis
                 readAllowed = isReadAllowed();
             }
         }
-        if (readAllowed) {
+        // NRT Replicas will not accept refresh listeners.
+        if (readAllowed && isSegmentReplicationAllowed() == false) {
             refreshListeners.addOrNotify(location, listener);
         } else {
             // we're not yet ready fo ready for reads, just ignore refresh cycles

server/src/test/java/org/opensearch/index/shard/SegmentReplicationIndexShardTests.java

@@ -120,6 +120,12 @@ public void testReplicationCheckpointNotNullForSegRep() throws IOException {
         closeShards(indexShard);
     }
 
+    public void testNRTReplicasDoNotAcceptRefreshListeners() throws IOException {
+        final IndexShard indexShard = newStartedShard(false, settings, new NRTReplicationEngineFactory());
+        indexShard.addRefreshListener(mock(Translog.Location.class), Assert::assertFalse);
+        closeShards(indexShard);
+    }
+
     public void testSegmentInfosAndReplicationCheckpointTuple() throws Exception {
         try (ReplicationGroup shards = createGroup(1, settings, new NRTReplicationEngineFactory())) {
             shards.startAll();