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Signed-off-by: guojialiang <[email protected]>

Author: guojialiang92

server/src/main/java/org/opensearch/indices/replication/common/CopyState.java

@@ -49,6 +49,9 @@ public CopyState(IndexShard shard) throws IOException {
         SegmentInfos segmentInfosSnapshot = segmentInfos.clone();
         Map<String, String> userData = segmentInfosSnapshot.getUserData();
         long maxSeqNo = Long.parseLong(userData.getOrDefault(SequenceNumbers.MAX_SEQ_NO, "-1"));
+        // In the scenario of vanilla segment replication. We need to ensure that after the primary promotion,
+        // the SegmentInfos#version of the primary shard is always greater than or equal to that of the replicas.
+        // At the same time, it is also necessary to ensure that there is no risk of data loss.
         userData.put(SequenceNumbers.MAX_SEQ_NO, Long.toString(Math.min(maxSeqNo, lastRefreshedCheckpoint)));
         segmentInfosSnapshot.setUserData(userData, false);