Retry download of RemoteFSTranslog to fix transient race conditions

server/src/internalClusterTest/java/org/opensearch/remotestore/RemoteIndexPrimaryRelocationIT.java

@@ -64,7 +64,6 @@ protected Settings featureFlagSettings() {
             .build();
     }
 
-    @AwaitsFix(bugUrl = "https://github.com/opensearch-project/OpenSearch/issues/9191")
     public void testPrimaryRelocationWhileIndexing() throws Exception {
         super.testPrimaryRelocationWhileIndexing();
     }

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

@@ -29,8 +29,10 @@
 import org.opensearch.repositories.blobstore.BlobStoreRepository;
 import org.opensearch.threadpool.ThreadPool;
 
+import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.nio.file.Files;
+import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
 import java.util.HashSet;
 import java.util.Locale;
@@ -68,6 +70,7 @@ public class RemoteFsTranslog extends Translog {
     private final SetOnce<Boolean> olderPrimaryCleaned = new SetOnce<>();
 
     private static final int REMOTE_DELETION_PERMITS = 2;
+    private static final int DOWNLOAD_RETRIES = 2;
     public static final String TRANSLOG = "translog";
 
     // Semaphore used to allow only single remote generation to happen at a time
@@ -161,7 +164,28 @@ public static void download(Repository repository, ShardId shardId, ThreadPool t
         RemoteFsTranslog.download(translogTransferManager, location, logger);
     }
 
-    public static void download(TranslogTransferManager translogTransferManager, Path location, Logger logger) throws IOException {
+    static void download(TranslogTransferManager translogTransferManager, Path location, Logger logger) throws IOException {
+        /*
+        In Primary to Primary relocation , there can be concurrent upload and download of translog.
+        While translog files are getting downloaded by new primary, it might hence be deleted by the primary
+        Hence we retry if tlog/ckp files are not found .
+
+        This doesn't happen in last download , where it is ensured that older primary has stopped modifying tlog data.
+         */
+        IOException ex = null;
+        for (int i = 0; i <= DOWNLOAD_RETRIES; i++) {
+            try {
+                downloadOnce(translogTransferManager, location, logger);
+                return;
+            } catch (FileNotFoundException | NoSuchFileException e) {
+                // continue till download retries
+                ex = e;
+            }
+        }
+        throw ex;
+    }
+
+    static private void downloadOnce(TranslogTransferManager translogTransferManager, Path location, Logger logger) throws IOException {
         logger.trace("Downloading translog files from remote");
         RemoteTranslogTransferTracker statsTracker = translogTransferManager.getRemoteTranslogTransferTracker();
         long prevDownloadBytesSucceeded = statsTracker.getDownloadBytesSucceeded();

server/src/test/java/org/opensearch/index/translog/RemoteFsTranslogTests.java

@@ -45,6 +45,8 @@
 import org.opensearch.index.seqno.LocalCheckpointTrackerTests;
 import org.opensearch.index.seqno.SequenceNumbers;
 import org.opensearch.index.translog.transfer.BlobStoreTransferService;
+import org.opensearch.index.translog.transfer.TranslogTransferManager;
+import org.opensearch.index.translog.transfer.TranslogTransferMetadata;
 import org.opensearch.indices.recovery.RecoverySettings;
 import org.opensearch.indices.replication.common.ReplicationType;
 import org.opensearch.repositories.blobstore.BlobStoreRepository;
@@ -59,12 +61,14 @@
 
 import java.io.Closeable;
 import java.io.EOFException;
+import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.ByteBuffer;
 import java.nio.channels.FileChannel;
 import java.nio.charset.Charset;
 import java.nio.file.Files;
+import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -98,6 +102,10 @@
 import static org.hamcrest.Matchers.empty;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.greaterThan;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.doAnswer;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
 
 @LuceneTestCase.SuppressFileSystems("ExtrasFS")
 
@@ -1466,6 +1474,42 @@ public void testCloseIntoReader() throws IOException {
         }
     }
 
+    public void testDownloadWithRetries() throws IOException {
+        long generation = 1, primaryTerm = 1;
+        Path location = createTempDir();
+        TranslogTransferMetadata translogTransferMetadata = new TranslogTransferMetadata(primaryTerm, generation, generation, 1);
+        Map<String, String> generationToPrimaryTermMapper = new HashMap<>();
+        generationToPrimaryTermMapper.put(String.valueOf(generation), String.valueOf(primaryTerm));
+        translogTransferMetadata.setGenerationToPrimaryTermMapper(generationToPrimaryTermMapper);
+
+        TranslogTransferManager mockTransfer = mock(TranslogTransferManager.class);
+        when(mockTransfer.readMetadata()).thenReturn(translogTransferMetadata);
+
+        // Always File not found
+        when(mockTransfer.downloadTranslog(any(), any(), any())).thenThrow(new NoSuchFileException("File not found"));
+        TranslogTransferManager finalMockTransfer = mockTransfer;
+        assertThrows(NoSuchFileException.class, () -> RemoteFsTranslog.download(finalMockTransfer, location, logger));
+
+        // File not found in first attempt . File found in second attempt.
+        mockTransfer = mock(TranslogTransferManager.class);
+        String msg = "File not found";
+        Exception toThrow = randomBoolean() ? new NoSuchFileException(msg) : new FileNotFoundException(msg);
+        when(mockTransfer.downloadTranslog(any(), any(), any())).thenThrow(toThrow).thenReturn(true);
+
+        AtomicLong downloadCounter = new AtomicLong();
+        doAnswer(invocation -> {
+            if (downloadCounter.incrementAndGet() <= 1) {
+                throw new NoSuchFileException("File not found");
+            } else if (downloadCounter.get() == 2) {
+                Files.createFile(location.resolve(Translog.getCommitCheckpointFileName(generation)));
+            }
+            return true;
+        }).when(mockTransfer).downloadTranslog(any(), any(), any());
+
+        // no exception thrown
+        RemoteFsTranslog.download(mockTransfer, location, logger);
+    }
+
     public class ThrowingBlobRepository extends FsRepository {
         private final Environment environment;