Java docs

Signed-off-by: Bukhtawar Khan <bukhtawa@amazon.com>

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

@@ -20,12 +20,24 @@
  */
 public interface TransferService {
 
+    /**
+     * Uploads the {@link TransferFileSnapshot} async, once the upload is complete the callback is invoked
+     * @param fileSnapshot the file snapshot to upload
+     * @param remotePath the remote path where upload should be made
+     * @param listener the callback to be invoked once upload completes successfully/fails
+     */
     void uploadBlobAsync(
         final TransferFileSnapshot fileSnapshot,
         Iterable<String> remotePath,
         ActionListener<TransferFileSnapshot> listener
     );
 
+    /**
+     * Uploads the {@link TransferFileSnapshot} blob
+     * @param fileSnapshot the file snapshot to upload
+     * @param remotePath the remote path where upload should be made
+     * @throws IOException
+     */
     void uploadBlob(final TransferFileSnapshot fileSnapshot, Iterable<String> remotePath) throws IOException;
 
 }

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

@@ -9,19 +9,34 @@
 package org.opensearch.index.translog.transfer;
 
 import org.opensearch.index.translog.transfer.FileSnapshot.TransferFileSnapshot;
+import org.opensearch.index.translog.transfer.FileSnapshot.CheckpointFileSnapshot;
+import org.opensearch.index.translog.transfer.FileSnapshot.TranslogFileSnapshot;
 
 import java.util.Set;
 
 /**
- * The snapshot of the files and it's metadata that is transferred to the {@link TransferService}
+ * The snapshot of the generational translog and checkpoint files and it's corresponding metadata that is transferred
+ * to the {@link TransferService}
  *
  * @opensearch.internal
  */
 public interface TransferSnapshot {
 
+    /**
+     * The snapshot of the checkpoint generational files
+     * @return the set of {@link CheckpointFileSnapshot}
+     */
     Set<TransferFileSnapshot> getCheckpointFileSnapshots();
 
+    /**
+     * The snapshot of the translog generational files
+     * @return the set of {@link TranslogFileSnapshot}
+     */
     Set<TransferFileSnapshot> getTranslogFileSnapshots();
 
+    /**
+     * The translog transfer metadata of this {@link TransferSnapshot}
+     * @return the translog transfer metadata
+     */
     TranslogTransferMetadata getTranslogTransferMetadata();
 }

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

@@ -19,7 +19,9 @@
 import java.util.Objects;
 
 /**
- * The metadata associated with every transfer {@link TransferSnapshot}
+ * The metadata associated with every transfer {@link TransferSnapshot}. The metadata is uploaded at the end of the
+ * tranlog and generational checkpoint uploads to mark the latest generation and the translog/checkpoint files that are
+ * still referenced by the last checkpoint.
  *
  * @opensearch.internal
  */

server/src/main/java/org/opensearch/index/translog/transfer/listener/FileTransferListener.java

@@ -17,7 +17,16 @@
  */
 public interface FileTransferListener {
 
+    /**
+     * Invoked when the transfer of a single {@link TransferFileSnapshot} succeeds
+     * @param fileSnapshot the corresponding file snapshot
+     */
     void onSuccess(TransferFileSnapshot fileSnapshot);
 
+    /**
+     * Invoked when the transfer of a single {@link TransferFileSnapshot} fails
+     * @param fileSnapshot the corresponding file snapshot
+     * @param e the exception while processing the {@link TransferFileSnapshot}
+     */
     void onFailure(TransferFileSnapshot fileSnapshot, Exception e);
 }

server/src/main/java/org/opensearch/index/translog/transfer/listener/TranslogTransferListener.java

@@ -19,7 +19,18 @@
  */
 public interface TranslogTransferListener {
 
+    /**
+     * Invoked when the transfer of {@link TransferSnapshot} succeeds
+     * @param transferSnapshot the transfer snapshot
+     * @throws IOException
+     */
     void onUploadComplete(TransferSnapshot transferSnapshot) throws IOException;
 
+    /**
+     * Invoked when the transfer of {@link TransferSnapshot} fails
+     * @param transferSnapshot the transfer snapshot
+     * @param ex the exception while processing the {@link TransferSnapshot}
+     * @throws IOException
+     */
     void onUploadFailed(TransferSnapshot transferSnapshot, Exception ex) throws IOException;
 }