From 2d762088935790ae7f17acf4cd711efc669edb88 Mon Sep 17 00:00:00 2001
From: Ashish Singh <ssashish@amazon.com>
Date: Wed, 6 Aug 2025 19:23:33 +0530
Subject: [PATCH 1/2] Fix segment replication bug during primary relocation

Signed-off-by: Ashish Singh <ssashish@amazon.com>
---
 .../AbstractSegmentReplicationTarget.java          | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/server/src/main/java/org/opensearch/indices/replication/AbstractSegmentReplicationTarget.java b/server/src/main/java/org/opensearch/indices/replication/AbstractSegmentReplicationTarget.java
index 2275034f1ec81..d7850409f5ee5 100644
--- a/server/src/main/java/org/opensearch/indices/replication/AbstractSegmentReplicationTarget.java
+++ b/server/src/main/java/org/opensearch/indices/replication/AbstractSegmentReplicationTarget.java
@@ -162,6 +162,20 @@ public void startReplication(ActionListener<Void> listener, BiConsumer<Replicati
         getCheckpointMetadata(checkpointInfoListener);
 
         checkpointInfoListener.whenComplete(checkpointInfo -> {
+            ReplicationCheckpoint getMetadataCheckpoint = checkpointInfo.getCheckpoint();
+            if (checkpoint.isAheadOf(getMetadataCheckpoint)) {
+                // Fixes https://github.com/opensearch-project/OpenSearch/issues/18490
+                listener.onFailure(
+                    new ReplicationFailedException(
+                        "Rejecting stale metadata checkpoint ["
+                            + getMetadataCheckpoint
+                            + "] since initial checkpoint ["
+                            + checkpoint
+                            + "] is ahead of it"
+                    )
+                );
+                return;
+            }
             updateCheckpoint(checkpointInfo.getCheckpoint(), checkpointUpdater);
             final List<StoreFileMetadata> filesToFetch = getFiles(checkpointInfo);
             state.setStage(SegmentReplicationState.Stage.GET_FILES);

From 3c475c1129a0662b35b0f0632eb3bb1251e6140b Mon Sep 17 00:00:00 2001
From: Ashish Singh <ssashish@amazon.com>
Date: Thu, 7 Aug 2025 10:43:09 +0530
Subject: [PATCH 2/2] Fix applicable for segrep local indexes only

Signed-off-by: Ashish Singh <ssashish@amazon.com>
---
 .../indices/replication/AbstractSegmentReplicationTarget.java   | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/server/src/main/java/org/opensearch/indices/replication/AbstractSegmentReplicationTarget.java b/server/src/main/java/org/opensearch/indices/replication/AbstractSegmentReplicationTarget.java
index d7850409f5ee5..5a21b10d04c06 100644
--- a/server/src/main/java/org/opensearch/indices/replication/AbstractSegmentReplicationTarget.java
+++ b/server/src/main/java/org/opensearch/indices/replication/AbstractSegmentReplicationTarget.java
@@ -163,7 +163,7 @@ public void startReplication(ActionListener<Void> listener, BiConsumer<Replicati
 
         checkpointInfoListener.whenComplete(checkpointInfo -> {
             ReplicationCheckpoint getMetadataCheckpoint = checkpointInfo.getCheckpoint();
-            if (checkpoint.isAheadOf(getMetadataCheckpoint)) {
+            if (indexShard.indexSettings().isSegRepLocalEnabled() && checkpoint.isAheadOf(getMetadataCheckpoint)) {
                 // Fixes https://github.com/opensearch-project/OpenSearch/issues/18490
                 listener.onFailure(
                     new ReplicationFailedException(