From 31c8427476e567071ea017837722b65b118955e2 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]" <github-actions[bot]@users.noreply.github.com>
Date: Thu, 7 Aug 2025 06:57:12 +0000
Subject: [PATCH] Fix segment replication bug during primary relocation
 (#18944)

* Fix segment replication bug during primary relocation

Signed-off-by: Ashish Singh <ssashish@amazon.com>

* Fix applicable for segrep local indexes only

Signed-off-by: Ashish Singh <ssashish@amazon.com>

---------

Signed-off-by: Ashish Singh <ssashish@amazon.com>
(cherry picked from commit 251cc3603e73405cc047e192663e8b5dbaa1c61d)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.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..5a21b10d04c06 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 (indexShard.indexSettings().isSegRepLocalEnabled() && 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);