initial commits

Signed-off-by: Sandeep Kumawat <2025sandeepkumawat@gmail.com>

Author: skumawat2025

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

@@ -91,6 +91,7 @@ public class RemoteFsTranslog extends Translog {
     private static final int SYNC_PERMIT = 1;
     private final Semaphore syncPermit = new Semaphore(SYNC_PERMIT);
     private final AtomicBoolean pauseSync = new AtomicBoolean(false);
+    boolean ckpAsMetadata;
 
     public RemoteFsTranslog(
         TranslogConfig config,
@@ -110,14 +111,16 @@ public RemoteFsTranslog(
         this.startedPrimarySupplier = startedPrimarySupplier;
         this.remoteTranslogTransferTracker = remoteTranslogTransferTracker;
         fileTransferTracker = new FileTransferTracker(shardId, remoteTranslogTransferTracker);
+        ckpAsMetadata = true;
         this.translogTransferManager = buildTranslogTransferManager(
             blobStoreRepository,
             threadPool,
             shardId,
             fileTransferTracker,
             remoteTranslogTransferTracker,
             indexSettings().getRemoteStorePathStrategy(),
-            remoteStoreSettings
+            remoteStoreSettings,
+            ckpAsMetadata
         );
         try {
             download(translogTransferManager, location, logger);
@@ -288,7 +291,8 @@ public static TranslogTransferManager buildTranslogTransferManager(
         FileTransferTracker fileTransferTracker,
         RemoteTranslogTransferTracker tracker,
         RemoteStorePathStrategy pathStrategy,
-        RemoteStoreSettings remoteStoreSettings
+        RemoteStoreSettings remoteStoreSettings,
+        boolean ckpAsMetadata
     ) {
         assert Objects.nonNull(pathStrategy);
         String indexUUID = shardId.getIndex().getUUID();
@@ -310,7 +314,16 @@ public static TranslogTransferManager buildTranslogTransferManager(
             .build();
         BlobPath mdPath = pathStrategy.generatePath(mdPathInput);
         BlobStoreTransferService transferService = new BlobStoreTransferService(blobStoreRepository.blobStore(), threadPool);
-        return new TranslogTransferManager(shardId, transferService, dataPath, mdPath, fileTransferTracker, tracker, remoteStoreSettings);
+        return new TranslogTransferManager(
+            shardId,
+            transferService,
+            dataPath,
+            mdPath,
+            fileTransferTracker,
+            tracker,
+            remoteStoreSettings,
+            ckpAsMetadata
+        );
     }
 
     @Override

server/src/main/java/org/opensearch/index/translog/transfer/FileSnapshot.java

@@ -22,6 +22,7 @@
 import java.nio.file.Path;
 import java.nio.file.StandardOpenOption;
 import java.util.Arrays;
+import java.util.Map;
 import java.util.Objects;
 
 /**
@@ -108,6 +109,7 @@ public static class TransferFileSnapshot extends FileSnapshot {
 
         private final long primaryTerm;
         private Long checksum;
+        private Map<String, String> metadata;
 
         public TransferFileSnapshot(Path path, long primaryTerm, Long checksum) throws IOException {
             super(path);
@@ -128,6 +130,14 @@ public long getPrimaryTerm() {
             return primaryTerm;
         }
 
+        public void setMetadata(Map<String, String> metadata) {
+            this.metadata = metadata;
+        }
+
+        public Map<String, String> getMetadata() {
+            return metadata;
+        }
+
         @Override
         public int hashCode() {
             return Objects.hash(primaryTerm, super.hashCode());

server/src/main/java/org/opensearch/index/translog/transfer/TransferSnapshot.java

@@ -12,6 +12,7 @@
 import org.opensearch.index.translog.transfer.FileSnapshot.TransferFileSnapshot;
 import org.opensearch.index.translog.transfer.FileSnapshot.TranslogFileSnapshot;
 
+import java.io.IOException;
 import java.util.Set;
 
 /**
@@ -39,4 +40,6 @@ public interface TransferSnapshot {
      * @return the translog transfer metadata
      */
     TranslogTransferMetadata getTranslogTransferMetadata();
+
+    Set<TransferFileSnapshot> getTranslogFileWithMetadataSnapshots() throws IOException;
 }

server/src/main/java/org/opensearch/index/translog/transfer/TranslogCheckpointTransferSnapshot.java

@@ -13,11 +13,15 @@
 
 import java.io.Closeable;
 import java.io.IOException;
+import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.ArrayList;
+import java.util.Base64;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedList;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
 import java.util.stream.Collectors;
@@ -64,6 +68,31 @@ public Set<TransferFileSnapshot> getTranslogFileSnapshots() {
         return translogCheckpointFileInfoTupleSet.stream().map(Tuple::v1).collect(Collectors.toSet());
     }
 
+    @Override
+    public Set<TransferFileSnapshot> getTranslogFileWithMetadataSnapshots() throws IOException {
+        Set<TransferFileSnapshot> toUploadList = new HashSet<>();
+        for (Tuple<TranslogFileSnapshot, CheckpointFileSnapshot> tuple : translogCheckpointFileInfoTupleSet) {
+            TranslogFileSnapshot translogFileSnapshot = tuple.v1();
+            CheckpointFileSnapshot checkpointFileSnapshot = tuple.v2();
+            translogFileSnapshot.setMetadata(buildMetadata(checkpointFileSnapshot.getPath()));
+            toUploadList.add(translogFileSnapshot);
+        }
+        return toUploadList;
+    }
+
+    public Map<String, String> buildMetadata(Path checkpointPath) throws IOException {
+        Map<String, String> metadata = new HashMap<>();
+        String ckpString = buildCheckpointDataAsBase64String(checkpointPath);
+        metadata.put("ckp-data", ckpString);
+        return metadata;
+    }
+
+    static String buildCheckpointDataAsBase64String(Path checkpointFilePath) throws IOException {
+        long fileSize = Files.size(checkpointFilePath);
+        byte[] fileBytes = Files.readAllBytes(checkpointFilePath);
+        return Base64.getEncoder().encodeToString(fileBytes);
+    }
+
     @Override
     public TranslogTransferMetadata getTranslogTransferMetadata() {
         return new TranslogTransferMetadata(

server/src/main/java/org/opensearch/index/translog/transfer/TranslogTransferManager.java

@@ -16,6 +16,7 @@
 import org.opensearch.common.SetOnce;
 import org.opensearch.common.blobstore.BlobMetadata;
 import org.opensearch.common.blobstore.BlobPath;
+import org.opensearch.common.blobstore.FetchBlobResult;
 import org.opensearch.common.blobstore.stream.write.WritePriority;
 import org.opensearch.common.io.VersionedCodecStreamWrapper;
 import org.opensearch.common.io.stream.BytesStreamOutput;
@@ -36,6 +37,7 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.ArrayList;
+import java.util.Base64;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
@@ -63,6 +65,7 @@ public class TranslogTransferManager {
     private final RemoteTranslogTransferTracker remoteTranslogTransferTracker;
     private final RemoteStoreSettings remoteStoreSettings;
     private static final int METADATA_FILES_TO_FETCH = 10;
+    boolean ckpAsMetadata;
 
     private final Logger logger;
 
@@ -79,7 +82,8 @@ public TranslogTransferManager(
         BlobPath remoteMetadataTransferPath,
         FileTransferTracker fileTransferTracker,
         RemoteTranslogTransferTracker remoteTranslogTransferTracker,
-        RemoteStoreSettings remoteStoreSettings
+        RemoteStoreSettings remoteStoreSettings,
+        boolean ckpAsMetadata
     ) {
         this.shardId = shardId;
         this.transferService = transferService;
@@ -89,6 +93,7 @@ public TranslogTransferManager(
         this.logger = Loggers.getLogger(getClass(), shardId);
         this.remoteTranslogTransferTracker = remoteTranslogTransferTracker;
         this.remoteStoreSettings = remoteStoreSettings;
+        this.ckpAsMetadata = ckpAsMetadata;
     }
 
     public RemoteTranslogTransferTracker getRemoteTranslogTransferTracker() {
@@ -110,8 +115,12 @@ public boolean transferSnapshot(TransferSnapshot transferSnapshot, TranslogTrans
         long prevUploadTimeInMillis = remoteTranslogTransferTracker.getTotalUploadTimeInMillis();
 
         try {
-            toUpload.addAll(fileTransferTracker.exclusionFilter(transferSnapshot.getTranslogFileSnapshots()));
-            toUpload.addAll(fileTransferTracker.exclusionFilter((transferSnapshot.getCheckpointFileSnapshots())));
+            if (ckpAsMetadata) {
+                toUpload.addAll(fileTransferTracker.exclusionFilter(transferSnapshot.getTranslogFileWithMetadataSnapshots()));
+            } else {
+                toUpload.addAll(fileTransferTracker.exclusionFilter(transferSnapshot.getTranslogFileSnapshots()));
+                toUpload.addAll(fileTransferTracker.exclusionFilter((transferSnapshot.getCheckpointFileSnapshots())));
+            }
             if (toUpload.isEmpty()) {
                 logger.trace("Nothing to upload for transfer");
                 return true;
@@ -236,15 +245,101 @@ public boolean downloadTranslog(String primaryTerm, String generation, Path loca
             generation,
             location
         );
-        // Download Checkpoint file from remote to local FS
         String ckpFileName = Translog.getCommitCheckpointFileName(Long.parseLong(generation));
-        downloadToFS(ckpFileName, location, primaryTerm);
-        // Download translog file from remote to local FS
         String translogFilename = Translog.getFilename(Long.parseLong(generation));
-        downloadToFS(translogFilename, location, primaryTerm);
+        if (ckpAsMetadata == false) {
+            // Download Checkpoint file from remote to local FS
+            downloadToFS(ckpFileName, location, primaryTerm);
+            // Download translog file from remote to local FS
+            downloadToFS(translogFilename, location, primaryTerm);
+        } else {
+            // Download translog.tlog file with object metadata from remote to local FS
+            Map<String, String> metadata = downloadTranslogToFSAndGetMetadata(translogFilename, location, primaryTerm, generation);
+            try {
+                assert metadata != null && !metadata.isEmpty() && metadata.containsKey("ckp-data");
+                recoverCkpFileFromMetadata(metadata, location, generation, translogFilename);
+            } catch (Exception e) {
+                throw new IOException("Failed to recover checkpoint file from remote", e);
+            }
+        }
         return true;
     }
 
+    private Map<String, String> downloadTranslogToFSAndGetMetadata(String fileName, Path location, String primaryTerm, String generation)
+        throws IOException {
+        Path filePath = location.resolve(fileName);
+        // Here, we always override the existing file if present.
+        // We need to change this logic when we introduce incremental download
+        deleteFileIfExists(filePath);
+
+        boolean downloadStatus = false;
+        long bytesToRead = 0, downloadStartTime = System.nanoTime();
+        Map<String, String> metadata;
+
+        FetchBlobResult inputStreamWithMetadata = transferService.downloadBlobWithMetadata(
+            remoteDataTransferPath.add(primaryTerm),
+            fileName
+        );
+        try {
+            InputStream inputStream = inputStreamWithMetadata.getInputStream();
+            metadata = inputStreamWithMetadata.getMetadata();
+
+            bytesToRead = inputStream.available();
+            Files.copy(inputStream, filePath);
+            downloadStatus = true;
+
+        } finally {
+            remoteTranslogTransferTracker.addDownloadTimeInMillis((System.nanoTime() - downloadStartTime) / 1_000_000L);
+            if (downloadStatus) {
+                remoteTranslogTransferTracker.addDownloadBytesSucceeded(bytesToRead);
+            }
+        }
+
+        // Mark in FileTransferTracker so that the same files are not uploaded at the time of translog sync
+        fileTransferTracker.add(fileName, true);
+
+        return metadata;
+    }
+
+    /**
+     * Process the provided metadata and tries to write the content of the checkpoint (ckp) file to the FS.
+     */
+    private void recoverCkpFileFromMetadata(Map<String, String> metadata, Path location, String generation, String fileName)
+        throws IOException {
+
+        boolean downloadStatus = false;
+        long bytesToRead = 0;
+        try {
+            String ckpFileName = Translog.getCommitCheckpointFileName(Long.parseLong(generation));
+            Path filePath = location.resolve(ckpFileName);
+            // Here, we always override the existing file if present.
+            deleteFileIfExists(filePath);
+
+            String ckpDataBase64 = metadata.get("ckp-data");
+            if (ckpDataBase64 == null) {
+                logger.error("Error processing metadata for translog file: {}", fileName);
+                throw new IllegalStateException(
+                    "Checkpoint file data (key - ckp-data) is expected but not found in metadata for file: " + fileName
+                );
+            }
+            byte[] ckpFileBytes = Base64.getDecoder().decode(ckpDataBase64);
+            bytesToRead = ckpFileBytes.length;
+
+            Files.write(filePath, ckpFileBytes);
+            downloadStatus = true;
+        } finally {
+            if (downloadStatus) {
+                remoteTranslogTransferTracker.addDownloadBytesSucceeded(bytesToRead);
+            }
+        }
+    }
+
+    public void deleteFileIfExists(Path filePath) throws IOException {
+        if (Files.exists(filePath)) {
+            Files.delete(filePath);
+        }
+    }
+
     private void downloadToFS(String fileName, Path location, String primaryTerm) throws IOException {
         Path filePath = location.resolve(fileName);
         // Here, we always override the existing file if present.
@@ -391,7 +486,11 @@ public void deleteGenerationAsync(long primaryTerm, Set<Long> generations, Runna
             // Add .ckp and .tlog file to translog file list which is located in basePath/<primaryTerm>
             String ckpFileName = Translog.getCommitCheckpointFileName(generation);
             String translogFileName = Translog.getFilename(generation);
-            translogFiles.addAll(List.of(ckpFileName, translogFileName));
+            if (ckpAsMetadata == false) {
+                translogFiles.addAll(List.of(ckpFileName, translogFileName));
+            } else {
+                translogFiles.add(translogFileName);
+            }
         });
         // Delete the translog and checkpoint files asynchronously
         deleteTranslogFilesAsync(primaryTerm, translogFiles, onCompletion);