[Backport 2.x] Add async segment file download support from remote store within OpenSearch core

server/src/internalClusterTest/java/org/opensearch/remotestore/multipart/RemoteStoreMultipartIT.java

@@ -86,6 +86,7 @@ public RepositoryMetadata buildRepositoryMetadata(DiscoveryNode node, String nam
         } else {
             return super.buildRepositoryMetadata(node, name);
         }
+
     }
 
     public void testRateLimitedRemoteUploads() throws Exception {

server/src/main/java/org/opensearch/index/IndexService.java

@@ -481,7 +481,7 @@ public synchronized IndexShard createShard(
             Store remoteStore = null;
             if (this.indexSettings.isRemoteStoreEnabled()) {
                 Directory remoteDirectory = remoteDirectoryFactory.newDirectory(this.indexSettings, path);
-                remoteStore = new Store(shardId, this.indexSettings, remoteDirectory, lock, Store.OnClose.EMPTY);
+                remoteStore = new Store(shardId, this.indexSettings, remoteDirectory, lock, Store.OnClose.EMPTY, path);
             }
 
             Directory directory = directoryFactory.newDirectory(this.indexSettings, path);
@@ -490,7 +490,8 @@ public synchronized IndexShard createShard(
                 this.indexSettings,
                 directory,
                 lock,
-                new StoreCloseListener(shardId, () -> eventListener.onStoreClosed(shardId))
+                new StoreCloseListener(shardId, () -> eventListener.onStoreClosed(shardId)),
+                path
             );
             eventListener.onStoreCreated(shardId);
             indexShard = new IndexShard(

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

@@ -63,6 +63,8 @@
 import org.opensearch.action.admin.indices.flush.FlushRequest;
 import org.opensearch.action.admin.indices.forcemerge.ForceMergeRequest;
 import org.opensearch.action.admin.indices.upgrade.post.UpgradeRequest;
+import org.opensearch.action.support.GroupedActionListener;
+import org.opensearch.action.support.PlainActionFuture;
 import org.opensearch.action.support.replication.PendingReplicationActions;
 import org.opensearch.action.support.replication.ReplicationResponse;
 import org.opensearch.cluster.metadata.DataStream;
@@ -97,7 +99,6 @@
 import org.opensearch.common.util.concurrent.RunOnce;
 import org.opensearch.common.util.concurrent.ThreadContext;
 import org.opensearch.common.util.io.IOUtils;
-import org.opensearch.common.util.set.Sets;
 import org.opensearch.core.Assertions;
 import org.opensearch.core.action.ActionListener;
 import org.opensearch.core.common.unit.ByteSizeValue;
@@ -200,6 +201,7 @@
 import java.nio.channels.FileChannel;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.NoSuchFileException;
+import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
@@ -859,7 +861,7 @@
                     synchronized (mutex) {
                         verifyRelocatingState();
                         replicationTracker.completeRelocationHandoff(); // make changes to primaryMode and relocated flag only under
-                                                                        // mutex
+                        // mutex
                     }
                 } catch (final Exception e) {
                     try {
@@ -3801,7 +3803,7 @@
             replicationTracker::isPrimaryMode,
             translogFactorySupplier.apply(indexSettings, shardRouting),
             isTimeSeriesDescSortOptimizationEnabled() ? DataStream.TIMESERIES_LEAF_SORTER : null // DESC @timestamp default order for
-                                                                                                 // timeseries
+            // timeseries
         );
     }
 
@@ -4862,39 +4864,71 @@
         Map<String, RemoteSegmentStoreDirectory.UploadedSegmentMetadata> uploadedSegments,
         boolean overrideLocal
     ) throws IOException {
-        List<String> downloadedSegments = new ArrayList<>();
-        List<String> skippedSegments = new ArrayList<>();
+        Set<String> toDownloadSegments = new HashSet<>();
+        Set<String> skippedSegments = new HashSet<>();
         String segmentNFile = null;
+
         try {
-            Set<String> localSegmentFiles = Sets.newHashSet(storeDirectory.listAll());
             if (overrideLocal) {
-                for (String file : localSegmentFiles) {
+                for (String file : storeDirectory.listAll()) {
                     storeDirectory.deleteFile(file);
                 }
             }
+
             for (String file : uploadedSegments.keySet()) {
                 long checksum = Long.parseLong(uploadedSegments.get(file).getChecksum());
                 if (overrideLocal || localDirectoryContains(storeDirectory, file, checksum) == false) {
-                    storeDirectory.copyFrom(sourceRemoteDirectory, file, file, IOContext.DEFAULT);
-                    downloadedSegments.add(file);
+                    toDownloadSegments.add(file);
                 } else {
                     skippedSegments.add(file);
                 }
-                if (targetRemoteDirectory != null) {
-                    targetRemoteDirectory.copyFrom(storeDirectory, file, file, IOContext.DEFAULT);
-                }
+
                 if (file.startsWith(IndexFileNames.SEGMENTS)) {
                     assert segmentNFile == null : "There should be only one SegmentInfosSnapshot file";
                     segmentNFile = file;
                 }
             }
+
+            if (toDownloadSegments.isEmpty() == false) {
+                try {
+                    final PlainActionFuture<Void> completionListener = PlainActionFuture.newFuture();
+                    downloadSegments(storeDirectory, sourceRemoteDirectory, targetRemoteDirectory, toDownloadSegments, completionListener);
+                    completionListener.actionGet();
+                } catch (Exception e) {
+                    throw new IOException("Error occurred when downloading segments from remote store", e);
+                }
+            }
         } finally {
-            logger.trace("Downloaded segments here: {}", downloadedSegments);
+            logger.trace("Downloaded segments here: {}", toDownloadSegments);
             logger.trace("Skipped download for segments here: {}", skippedSegments);
         }
+
         return segmentNFile;
     }
 
+    private void downloadSegments(
+        Directory storeDirectory,
+        RemoteSegmentStoreDirectory sourceRemoteDirectory,
+        RemoteSegmentStoreDirectory targetRemoteDirectory,
+        Set<String> toDownloadSegments,
+        ActionListener<Void> completionListener
+    ) {
+        final Path indexPath = store.shardPath() == null ? null : store.shardPath().resolveIndex();
+        final GroupedActionListener<Void> batchDownloadListener = new GroupedActionListener<>(
+            ActionListener.map(completionListener, v -> null),
+            toDownloadSegments.size()
+        );
+
+        final ActionListener<String> segmentsDownloadListener = ActionListener.map(batchDownloadListener, fileName -> {
+            if (targetRemoteDirectory != null) {
+                targetRemoteDirectory.copyFrom(storeDirectory, fileName, fileName, IOContext.DEFAULT);
+            }
+            return null;
+        });
+
+        toDownloadSegments.forEach(file -> sourceRemoteDirectory.copyTo(file, storeDirectory, indexPath, segmentsDownloadListener));
+    }
+
     private boolean localDirectoryContains(Directory localDirectory, String file, long checksum) {
         try (IndexInput indexInput = localDirectory.openInput(file, IOContext.DEFAULT)) {
             if (checksum == CodecUtil.retrieveChecksum(indexInput)) {

server/src/main/java/org/opensearch/index/store/RemoteSegmentStoreDirectory.java

@@ -24,6 +24,7 @@
 import org.apache.lucene.store.IndexOutput;
 import org.apache.lucene.util.Version;
 import org.opensearch.common.UUIDs;
+import org.opensearch.common.blobstore.AsyncMultiStreamBlobContainer;
 import org.opensearch.common.io.VersionedCodecStreamWrapper;
 import org.opensearch.common.lucene.store.ByteArrayIndexInput;
 import org.opensearch.core.action.ActionListener;
@@ -40,6 +41,7 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.file.NoSuchFileException;
+import java.nio.file.Path;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
@@ -434,6 +436,41 @@ public void copyFrom(Directory from, String src, IOContext context, ActionListen
         }
     }
 
+    /**
+     * Copies an existing {@code source} file from this directory to a non-existent file (also
+     * named {@code source}) in either {@code destinationDirectory} or {@code destinationPath}.
+     * If the blob container backing this directory supports multipart downloads, the {@code source}
+     * file will be downloaded (potentially in multiple concurrent parts) directly to
+     * {@code destinationPath}. This method will return immediately and {@code fileCompletionListener}
+     * will be notified upon completion.
+     * <p>
+     * If multipart downloads are not supported, then {@code source} file will be copied to a file named
+     * {@code source} in a single part to {@code destinationDirectory}. The download will happen on the
+     * calling thread and {@code fileCompletionListener} will be notified synchronously before this
+     * method returns.
+     *
+     * @param source The source file name
+     * @param destinationDirectory The destination directory (if multipart is not supported)
+     * @param destinationPath The destination path (if multipart is supported)
+     * @param fileCompletionListener The listener to notify of completion
+     */
+    public void copyTo(String source, Directory destinationDirectory, Path destinationPath, ActionListener<String> fileCompletionListener) {
+        final String blobName = getExistingRemoteFilename(source);
+        if (destinationPath != null && remoteDataDirectory.getBlobContainer() instanceof AsyncMultiStreamBlobContainer) {
+            final AsyncMultiStreamBlobContainer blobContainer = (AsyncMultiStreamBlobContainer) remoteDataDirectory.getBlobContainer();
+            final Path destinationFilePath = destinationPath.resolve(source);
+            blobContainer.asyncBlobDownload(blobName, destinationFilePath, threadPool, fileCompletionListener);
+        } else {
+            // Fallback to older mechanism of downloading the file
+            try {
+                destinationDirectory.copyFrom(this, source, source, IOContext.DEFAULT);
+                fileCompletionListener.onResponse(source);
+            } catch (IOException e) {
+                fileCompletionListener.onFailure(e);
+            }
+        }
+    }
+
     /**
      * This acquires a lock on a given commit by creating a lock file in lock directory using {@code FileLockInfo}
      *

server/src/main/java/org/opensearch/index/store/Store.java

@@ -66,6 +66,7 @@
 import org.apache.lucene.util.Version;
 import org.opensearch.ExceptionsHelper;
 import org.opensearch.common.UUIDs;
+import org.opensearch.common.annotation.InternalApi;
 import org.opensearch.common.io.stream.BytesStreamOutput;
 import org.opensearch.common.logging.Loggers;
 import org.opensearch.common.lucene.Lucene;
@@ -92,6 +93,7 @@
 import org.opensearch.index.seqno.SequenceNumbers;
 import org.opensearch.index.shard.AbstractIndexShardComponent;
 import org.opensearch.index.shard.IndexShard;
+import org.opensearch.index.shard.ShardPath;
 import org.opensearch.index.translog.Translog;
 
 import java.io.Closeable;
@@ -179,6 +181,7 @@ public class Store extends AbstractIndexShardComponent implements Closeable, Ref
     private final ReentrantReadWriteLock metadataLock = new ReentrantReadWriteLock();
     private final ShardLock shardLock;
     private final OnClose onClose;
+    private final ShardPath shardPath;
 
     // used to ref count files when a new Reader is opened for PIT/Scroll queries
     // prevents segment files deletion until the PIT/Scroll expires or is discarded
@@ -192,17 +195,25 @@ protected void closeInternal() {
     };
 
     public Store(ShardId shardId, IndexSettings indexSettings, Directory directory, ShardLock shardLock) {
-        this(shardId, indexSettings, directory, shardLock, OnClose.EMPTY);
+        this(shardId, indexSettings, directory, shardLock, OnClose.EMPTY, null);
     }
 
-    public Store(ShardId shardId, IndexSettings indexSettings, Directory directory, ShardLock shardLock, OnClose onClose) {
+    public Store(
+        ShardId shardId,
+        IndexSettings indexSettings,
+        Directory directory,
+        ShardLock shardLock,
+        OnClose onClose,
+        ShardPath shardPath
+    ) {
         super(shardId, indexSettings);
         final TimeValue refreshInterval = indexSettings.getValue(INDEX_STORE_STATS_REFRESH_INTERVAL_SETTING);
         logger.debug("store stats are refreshed with refresh_interval [{}]", refreshInterval);
         ByteSizeCachingDirectory sizeCachingDir = new ByteSizeCachingDirectory(directory, refreshInterval);
         this.directory = new StoreDirectory(sizeCachingDir, Loggers.getLogger("index.store.deletes", shardId));
         this.shardLock = shardLock;
         this.onClose = onClose;
+        this.shardPath = shardPath;
         assert onClose != null;
         assert shardLock != null;
         assert shardLock.getShardId().equals(shardId);
@@ -213,6 +224,11 @@ public Directory directory() {
         return directory;
     }
 
+    @InternalApi
+    public ShardPath shardPath() {
+        return shardPath;
+    }
+
     /**
      * Returns the last committed segments info for this store
      *

server/src/main/java/org/opensearch/indices/replication/RemoteStoreReplicationSource.java

@@ -13,18 +13,20 @@
 import org.apache.lucene.index.SegmentInfos;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.FilterDirectory;
-import org.apache.lucene.store.IOContext;
 import org.apache.lucene.util.Version;
+import org.opensearch.action.support.GroupedActionListener;
 import org.opensearch.common.concurrent.GatedCloseable;
 import org.opensearch.core.action.ActionListener;
 import org.opensearch.index.shard.IndexShard;
 import org.opensearch.index.shard.IndexShardState;
+import org.opensearch.index.shard.ShardPath;
 import org.opensearch.index.store.RemoteSegmentStoreDirectory;
 import org.opensearch.index.store.Store;
 import org.opensearch.index.store.StoreFileMetadata;
 import org.opensearch.index.store.remote.metadata.RemoteSegmentMetadata;
 import org.opensearch.indices.replication.checkpoint.ReplicationCheckpoint;
 
+import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
@@ -106,31 +108,49 @@ public void getSegmentFiles(
             logger.trace("Downloading segments files from remote store {}", filesToFetch);
 
             RemoteSegmentMetadata remoteSegmentMetadata = remoteDirectory.readLatestMetadataFile();
-            List<StoreFileMetadata> downloadedSegments = new ArrayList<>();
+            List<StoreFileMetadata> toDownloadSegments = new ArrayList<>();
             Collection<String> directoryFiles = List.of(indexShard.store().directory().listAll());
             if (remoteSegmentMetadata != null) {
                 try {
                     indexShard.store().incRef();
                     indexShard.remoteStore().incRef();
                     final Directory storeDirectory = indexShard.store().directory();
+                    final ShardPath shardPath = indexShard.shardPath();
                     for (StoreFileMetadata fileMetadata : filesToFetch) {
                         String file = fileMetadata.name();
                         assert directoryFiles.contains(file) == false : "Local store already contains the file " + file;
-                        storeDirectory.copyFrom(remoteDirectory, file, file, IOContext.DEFAULT);
-                        downloadedSegments.add(fileMetadata);
+                        toDownloadSegments.add(fileMetadata);
                     }
-                    logger.trace("Downloaded segments from remote store {}", downloadedSegments);
+                    downloadSegments(storeDirectory, remoteDirectory, toDownloadSegments, shardPath, listener);
+                    logger.trace("Downloaded segments from remote store {}", toDownloadSegments);
                 } finally {
                     indexShard.store().decRef();
                     indexShard.remoteStore().decRef();
                 }
             }
-            listener.onResponse(new GetSegmentFilesResponse(downloadedSegments));
         } catch (Exception e) {
             listener.onFailure(e);
         }
     }
 
+    private void downloadSegments(
+        Directory storeDirectory,
+        RemoteSegmentStoreDirectory remoteStoreDirectory,
+        List<StoreFileMetadata> toDownloadSegments,
+        ShardPath shardPath,
+        ActionListener<GetSegmentFilesResponse> completionListener
+    ) {
+        final Path indexPath = shardPath == null ? null : shardPath.resolveIndex();
+        final GroupedActionListener<Void> batchDownloadListener = new GroupedActionListener<>(
+            ActionListener.map(completionListener, v -> new GetSegmentFilesResponse(toDownloadSegments)),
+            toDownloadSegments.size()
+        );
+        ActionListener<String> segmentsDownloadListener = ActionListener.map(batchDownloadListener, result -> null);
+        toDownloadSegments.forEach(
+            fileMetadata -> remoteStoreDirectory.copyTo(fileMetadata.name(), storeDirectory, indexPath, segmentsDownloadListener)
+        );
+    }
+
     @Override
     public String getDescription() {
         return "RemoteStoreReplicationSource";

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

@@ -1718,7 +1718,7 @@ public Set<String> getPendingDeletions() throws IOException {
             }
         };
 
-        try (Store store = createStore(shardId, new IndexSettings(metadata, Settings.EMPTY), directory)) {
+        try (Store store = createStore(shardId, new IndexSettings(metadata, Settings.EMPTY), directory, shardPath)) {
             IndexShard shard = newShard(
                 shardRouting,
                 shardPath,