Incorporate PR review comments

Signed-off-by: Ashish Singh <ssashish@amazon.com>

Author: ashking94

server/src/main/java/org/opensearch/index/translog/InternalTranslogManager.java

@@ -430,10 +430,9 @@ public String getTranslogUUID() {
      * @return if the translog should be flushed
      */
     public boolean shouldPeriodicallyFlush(long localCheckpointOfLastCommit, long flushThreshold) {
-        long minRefSeqNo = translog instanceof RemoteFsTranslog
-            ? ((RemoteFsTranslog) translog).getMinSeqNoToKeep()
-            : localCheckpointOfLastCommit + 1;
-        final long minReferencedTranslogGeneration = translog.getMinGenerationForSeqNo(minRefSeqNo).translogFileGeneration;
+        // This is the minimum seqNo that is referred in translog and considered for calculating translog size
+        long minTranslogRefSeqNo = translog.getMinUnreferencedSeqNoInSegments(localCheckpointOfLastCommit + 1);
+        final long minReferencedTranslogGeneration = translog.getMinGenerationForSeqNo(minTranslogRefSeqNo).translogFileGeneration;
         if (translog.sizeInBytesByMinGen(minReferencedTranslogGeneration) < flushThreshold) {
             return false;
         }

server/src/main/java/org/opensearch/index/translog/RemoteFsTranslog.java

@@ -545,7 +545,8 @@ public void onUploadFailed(TransferSnapshot transferSnapshot, Exception ex) thro
         }
     }
 
-    long getMinSeqNoToKeep() {
+    @Override
+    public long getMinUnreferencedSeqNoInSegments(long minUnrefCheckpointInLastCommit) {
         return minSeqNoToKeep;
     }
 }

server/src/main/java/org/opensearch/index/translog/Translog.java

@@ -2034,4 +2034,8 @@ public static String createEmptyTranslog(
         writer.close();
         return uuid;
     }
+
+    public long getMinUnreferencedSeqNoInSegments(long minUnrefCheckpointInLastCommit) {
+        return minUnrefCheckpointInLastCommit;
+    }
 }

server/src/main/java/org/opensearch/indices/recovery/RemoteRecoveryTargetHandler.java

@@ -134,7 +134,7 @@ public void prepareForTranslogOperations(int totalTranslogOps, ActionListener<Vo
         final ActionListener<TransportResponse.Empty> responseListener = ActionListener.map(listener, r -> null);
         if (remoteStoreEnabled) {
             // If remote store is enabled, during the prepare_translog phase, translog is also downloaded on the
-            // target host along with incremental segments download. This
+            // target host along with incremental segments download.
             retryableTransportClient.executeRetryableAction(action, request, translogOpsRequestOptions, responseListener, reader);
         } else {
             retryableTransportClient.executeRetryableAction(action, request, responseListener, reader);