Add getHistoryOperationsFromTranslog method to fetch the hostory snapshot from translogs

Signed-off-by: Ankit Kala <[email protected]>

Author: ankitkala

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

@@ -2352,6 +2352,16 @@ public Translog.Snapshot getHistoryOperations(String reason, long startingSeqNo,
         return getEngine().newChangesSnapshot(reason, startingSeqNo, endSeqNo, true, accurateCount);
     }
 
+    /**
+     * Creates a new history snapshot from the translog instead of the lucene index. Required for cross cluster replication.
+     * Use the recommended {@link #getHistoryOperations(String, long, long, boolean)} method for other cases.
+     * Depending on how translog durability is configured, this method might/might not return the snapshot. For e.g,
+     * If the translog has been configured with no-durability, it'll return UnsupportedOperationException.
+     */
+    public Translog.Snapshot getHistoryOperationsFromTranslog(long startingSeqNo, long endSeqNo) throws IOException {
+        return getEngine().translogManager().newChangesSnapshot(startingSeqNo, endSeqNo, true);
+    }
+
     /**
      * Checks if we have a completed history of operations since the given starting seqno (inclusive).
      * This method should be called after acquiring the retention lock; See {@link #acquireHistoryRetentionLock()}

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

@@ -97,6 +97,11 @@ public void rollTranslogGeneration() throws TranslogException {
         }
     }
 
+    @Override
+    public Translog.Snapshot newChangesSnapshot(long fromSeqNo, long toSeqNo, boolean requiredFullRange) throws IOException {
+        return translog.newSnapshot(fromSeqNo, toSeqNo, requiredFullRange);
+    }
+
     /**
      * Performs recovery from the transaction log up to {@code recoverUpToSeqNo} (inclusive).
      * This operation will close the engine if the recovery fails.

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

@@ -112,4 +112,9 @@ public Translog.Operation readOperation(Translog.Location location) throws IOExc
     public Translog.Location add(Translog.Operation operation) throws IOException {
         return new Translog.Location(0, 0, 0);
     }
+
+    @Override
+    public Translog.Snapshot newChangesSnapshot(long fromSeqNo, long toSeqNo, boolean requiredFullRange) throws IOException {
+        throw new UnsupportedOperationException("Translog snapshot unsupported with no-op translogs");
+    }
 }

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

@@ -33,6 +33,11 @@ public interface TranslogManager {
      */
     int recoverFromTranslog(TranslogRecoveryRunner translogRecoveryRunner, long localCheckpoint, long recoverUpToSeqNo) throws IOException;
 
+    /**
+     * Creates a new history snapshot from the translog file instead of the lucene index.
+     */
+    Translog.Snapshot newChangesSnapshot(long fromSeqNo, long toSeqNo, boolean requiredFullRange) throws IOException;
+
     /**
      * Checks if the underlying storage sync is required.
      */

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

@@ -66,4 +66,9 @@ public int recoverFromTranslog(TranslogRecoveryRunner translogRecoveryRunner, lo
     public void skipTranslogRecovery() {
         // Do nothing.
     }
+
+    @Override
+    public Translog.Snapshot newChangesSnapshot(long fromSeqNo, long toSeqNo, boolean requiredFullRange) throws IOException {
+        throw new UnsupportedOperationException("Translog snapshot unsupported with no-op translogs");
+    }
 }