Adding JavaDocs and fixing divide by zero errors on UTs

Signed-off-by: Shourya Dutta Biswas <114977491+shourya035@users.noreply.github.com>

server/src/main/java/org/opensearch/index/remote/RemoteRefreshSegmentTracker.java

@@ -52,6 +52,9 @@ public class RemoteRefreshSegmentTracker {
      */
     private volatile long localRefreshClockTimeMs;
 
+    /**
+     * Time in milliseconds for the last successful segment download
+     */
     private volatile long lastDownloadTimestampMs;
 
     /**
@@ -101,8 +104,19 @@ public class RemoteRefreshSegmentTracker {
      */
     private volatile long uploadBytesSucceeded;
 
+    /**
+     * Cumulative sum of size in bytes of segment files for which download has started.
+     */
     private volatile long downloadBytesStarted;
+
+    /**
+     * Cumulative sum of size in bytes of segment files for which download has failed.
+     */
     private volatile long downloadBytesFailed;
+
+    /**
+     * Cumulative sum of size in bytes of segment files for which download has succeeded.
+     */
     private volatile long downloadBytesSucceeded;
 
     /**
@@ -120,8 +134,19 @@ public class RemoteRefreshSegmentTracker {
      */
     private volatile long totalUploadsSucceeded;
 
+    /**
+     * Cumulative sum of count of segment file downloads that have started.
+     */
     private volatile long totalDownloadsStarted;
+
+    /**
+     * Cumulative sum of count of segment file downloads that have succeeded.
+     */
     private volatile long totalDownloadsSucceeded;
+
+    /**
+     * Cumulative sum of count of segment file downloads that have failed.
+     */
     private volatile long totalDownloadsFailed;
 
     /**
@@ -165,6 +190,10 @@ public class RemoteRefreshSegmentTracker {
      */
     private final Object uploadBytesMutex = new Object();
 
+    /**
+     * Provides moving average over the last N total size in bytes of segment files downloaded from the remote store.
+     * N is window size. Wrapped with {@code AtomicReference} for dynamic changes in window size.
+     */
     private final AtomicReference<MovingAverage> downloadBytesMovingAverageReference;
 
     private final Object downloadBytesMutex = new Object();
@@ -177,18 +206,26 @@ public class RemoteRefreshSegmentTracker {
 
     private final Object uploadBytesPerSecMutex = new Object();
 
+    /**
+     * Provides moving average over the last N upload speed (in bytes/s) of segment files downloaded from the remote store.
+     * N is window size. Wrapped with {@code AtomicReference} for dynamic changes in window size.
+     */
     private final AtomicReference<MovingAverage> downloadBytesPerSecMovingAverageReference;
 
     private final Object downloadBytesPerSecMutex = new Object();
 
     /**
-     * Provides moving average over the last N overall upload time (in nanos) as part of remote refresh.N is window size.
+     * Provides moving average over the last N overall upload time (in millis) as part of remote refresh.N is window size.
      * Wrapped with {@code AtomicReference} for dynamic changes in window size.
      */
     private final AtomicReference<MovingAverage> uploadTimeMsMovingAverageReference;
 
     private final Object uploadTimeMsMutex = new Object();
 
+    /**
+     * Provides moving average over the last N overall download time (in millis) of segments downloaded from the remote store.
+     * Wrapped with {@code AtomicReference} for dynamic changes in window size.
+     */
     private final AtomicReference<MovingAverage> downloadTimeMovingAverageReference;
 
     private final Object downloadTimeMutex = new Object();
@@ -851,5 +888,4 @@ public void writeTo(StreamOutput out) throws IOException {
             out.writeLong(bytesLag);
         }
     }
-
 }

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

@@ -44,7 +44,6 @@
 import org.apache.lucene.index.LeafReader;
 import org.apache.lucene.index.SegmentInfos;
 import org.apache.lucene.index.Term;
-import org.apache.lucene.index.IndexFileNames;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.search.QueryCachingPolicy;
 import org.apache.lucene.search.ReferenceManager;
@@ -4771,14 +4770,14 @@ private String copySegmentFiles(
                 RemoteSegmentStoreDirectory.UploadedSegmentMetadata segmentMetadata = uploadedSegments.get(file);
                 long checksum = Long.parseLong(uploadedSegments.get(file).getChecksum());
                 if (overrideLocal || localDirectoryContains(storeDirectory, file, checksum) == false) {
-                    long startTimeInMs = System.currentTimeMillis();
+                    long startTimeInNs = System.nanoTime();
                     long segmentSizeInBytes = segmentMetadata.getLength();
                     beforeSegmentDownload(downloadStatsTracker, segmentSizeInBytes);
                     try {
                         storeDirectory.copyFrom(sourceRemoteDirectory, file, file, IOContext.DEFAULT);
                         storeDirectory.sync(Collections.singleton(file));
                         downloadedSegments.add(file);
-                        afterSegmentDownloadCompleted(downloadStatsTracker, segmentSizeInBytes, startTimeInMs);
+                        afterSegmentDownloadCompleted(downloadStatsTracker, segmentSizeInBytes, startTimeInNs);
                     } catch (IOException e) {
                         afterSegmentDownloadFailed(downloadStatsTracker, segmentSizeInBytes);
                         throw e;
@@ -4826,15 +4825,14 @@ private void afterSegmentDownloadCompleted(
         long downloadedFileSize,
         long startTimeInNs
     ) {
-        long currentTime = System.currentTimeMillis();
-        downloadStatsTracker.updateLastDownloadTimestampMs(currentTime);
+        long currentTimeInNs = System.nanoTime();
+        downloadStatsTracker.updateLastDownloadTimestampMs(System.currentTimeMillis());
         downloadStatsTracker.incrementTotalDownloadsSucceeded();
         downloadStatsTracker.addDownloadBytes(downloadedFileSize);
         downloadStatsTracker.addDownloadBytesSucceeded(downloadedFileSize);
-        long timeTakenInMS = currentTime - startTimeInNs;
+        long timeTakenInMS = Math.max(1, TimeValue.nsecToMSec(currentTimeInNs - startTimeInNs));
         downloadStatsTracker.addDownloadTime(timeTakenInMS);
         downloadStatsTracker.addDownloadBytesPerSec((downloadedFileSize * 1_000L) / timeTakenInMS);
-
     }
 
     private void afterSegmentDownloadFailed(RemoteRefreshSegmentTracker downloadStatsTracker, long failedFileSize) {

server/src/test/java/org/opensearch/action/admin/cluster/remotestore/stats/TransportRemoteStoreStatsActionTests.java

@@ -108,7 +108,7 @@ public void tearDown() throws Exception {
         clusterService.close();
     }
 
-    public void testOnlyPrimaryShards() throws Exception {
+    public void testAllShardCopies() throws Exception {
         FeatureFlagSetter.set(FeatureFlags.REMOTE_STORE);
         RoutingTable routingTable = RoutingTable.builder().addAsNew(remoteStoreIndexMetadata).build();
         Metadata metadata = Metadata.builder().put(remoteStoreIndexMetadata, false).build();
@@ -125,7 +125,7 @@ public void testOnlyPrimaryShards() throws Exception {
             new String[] { INDEX.getName() }
         );
 
-        assertEquals(shardsIterator.size(), 2);
+        assertEquals(shardsIterator.size(), 4);
     }
 
     public void testOnlyLocalShards() throws Exception {
@@ -153,10 +153,10 @@ public void testOnlyLocalShards() throws Exception {
         remoteStoreStatsRequest.local(true);
         ShardsIterator shardsIterator = statsAction.shards(clusterService.state(), remoteStoreStatsRequest, concreteIndices);
 
-        assertEquals(shardsIterator.size(), 1);
+        assertEquals(shardsIterator.size(), 2);
     }
 
-    public void testOnlyRemoteStoreEnabledShards() throws Exception {
+    public void testOnlyRemoteStoreEnabledShardCopies() throws Exception {
         FeatureFlagSetter.set(FeatureFlags.REMOTE_STORE);
         Index NEW_INDEX = new Index("newIndex", "newUUID");
         IndexMetadata indexMetadataWithoutRemoteStore = IndexMetadata.builder(NEW_INDEX.getName())
@@ -189,6 +189,6 @@ public void testOnlyRemoteStoreEnabledShards() throws Exception {
             new String[] { INDEX.getName() }
         );
 
-        assertEquals(shardsIterator.size(), 2);
+        assertEquals(shardsIterator.size(), 4);
     }
 }