Add getHistoryOperationsFromTranslog method to fetch the history snap…

…shot from translogs (opensearch-project#3948)

* Add getHistoryOperationsFromTranslog method to fetch the hostory snapshot from translogs

Signed-off-by: Ankit Kala <ankikala@amazon.com>

CHANGELOG.md

@@ -34,6 +34,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Add index specific setting for remote repository ([#4253](https://github.com/opensearch-project/OpenSearch/pull/4253))
 - [Segment Replication] Update replicas to commit SegmentInfos instead of relying on SIS files from primary shards. ([#4402](https://github.com/opensearch-project/OpenSearch/pull/4402))
 - Add DecommissionService and helper to execute awareness attribute decommissioning ([#4084](https://github.com/opensearch-project/OpenSearch/pull/4084))
+- [CCR] Add getHistoryOperationsFromTranslog method to fetch the history snapshot from translogs ([#3948](https://github.com/opensearch-project/OpenSearch/pull/3948))
 
 ### Deprecated
 

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

@@ -2357,6 +2357,17 @@ 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.
+     * This method should only be invoked if Segment Replication or Remote Store is not enabled.
+     */
+    public Translog.Snapshot getHistoryOperationsFromTranslog(long startingSeqNo, long endSeqNo) throws IOException {
+        assert (indexSettings.isSegRepEnabled() || indexSettings.isRemoteStoreEnabled()) == false
+            : "unsupported operation for segment replication enabled indices or remote store backed indices";
+        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

@@ -98,6 +98,11 @@ 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

@@ -68,4 +68,9 @@ 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");
+    }
 }

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

@@ -1196,6 +1196,66 @@ public void testAcquireReplicaPermitAdvanceMaxSeqNoOfUpdates() throws Exception
         closeShards(replica);
     }
 
+    public void testGetChangesSnapshotThrowsAssertForSegRep() throws IOException {
+        final ShardId shardId = new ShardId("index", "_na_", 0);
+        final ShardRouting shardRouting = TestShardRouting.newShardRouting(
+            shardId,
+            randomAlphaOfLength(8),
+            true,
+            ShardRoutingState.INITIALIZING,
+            RecoverySource.EmptyStoreRecoverySource.INSTANCE
+        );
+        final Settings settings = Settings.builder()
+            .put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT)
+            .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 2)
+            .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
+            .put(IndexMetadata.SETTING_REPLICATION_TYPE, ReplicationType.SEGMENT.toString())
+            .build();
+        final IndexMetadata.Builder indexMetadata = IndexMetadata.builder(shardRouting.getIndexName()).settings(settings).primaryTerm(0, 1);
+        final AtomicBoolean synced = new AtomicBoolean();
+        final IndexShard primaryShard = newShard(
+            shardRouting,
+            indexMetadata.build(),
+            null,
+            new InternalEngineFactory(),
+            () -> synced.set(true),
+            RetentionLeaseSyncer.EMPTY,
+            null
+        );
+        expectThrows(AssertionError.class, () -> primaryShard.getHistoryOperationsFromTranslog(0, 1));
+        closeShard(primaryShard, false);
+    }
+
+    public void testGetChangesSnapshotThrowsAssertForRemoteStore() throws IOException {
+        final ShardId shardId = new ShardId("index", "_na_", 0);
+        final ShardRouting shardRouting = TestShardRouting.newShardRouting(
+            shardId,
+            randomAlphaOfLength(8),
+            true,
+            ShardRoutingState.INITIALIZING,
+            RecoverySource.EmptyStoreRecoverySource.INSTANCE
+        );
+        final Settings settings = Settings.builder()
+            .put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT)
+            .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 2)
+            .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
+            .put(IndexMetadata.SETTING_REMOTE_STORE_ENABLED, true)
+            .build();
+        final IndexMetadata.Builder indexMetadata = IndexMetadata.builder(shardRouting.getIndexName()).settings(settings).primaryTerm(0, 1);
+        final AtomicBoolean synced = new AtomicBoolean();
+        final IndexShard primaryShard = newShard(
+            shardRouting,
+            indexMetadata.build(),
+            null,
+            new InternalEngineFactory(),
+            () -> synced.set(true),
+            RetentionLeaseSyncer.EMPTY,
+            null
+        );
+        expectThrows(AssertionError.class, () -> primaryShard.getHistoryOperationsFromTranslog(0, 1));
+        closeShard(primaryShard, false);
+    }
+
     public void testGlobalCheckpointSync() throws IOException {
         // create the primary shard with a callback that sets a boolean when the global checkpoint sync is invoked
         final ShardId shardId = new ShardId("index", "_na_", 0);