assert live doc has highest seqno

Author: dnhatn

server/src/main/java/org/elasticsearch/common/lucene/uid/PerThreadIDVersionAndSeqNoLookup.java

@@ -160,6 +160,8 @@ DocIdAndSeqNo lookupSeqNo(BytesRef id, LeafReaderContext context) throws IOExcep
                         // The live document must always be the latest copy, thus we can early terminate here.
                         // If a nested docs is live, we return the first doc which doesn't have term (only the last doc has term).
                         // This should not be an issue since we no longer use primary term as tier breaker when comparing operations.
+                        assert result == null || result.seqNo <= seqNo :
+                            "the live doc does not have the highest seq_no; live_seq_no=" + seqNo + " < deleted_seq_no=" + result.seqNo;
                         return new DocIdAndSeqNo(docID, seqNo, context, isLive);
                     }
                     if (result == null || result.seqNo < seqNo) {

server/src/main/java/org/elasticsearch/common/lucene/uid/VersionsAndSeqNoResolver.java

@@ -165,6 +165,8 @@ public static DocIdAndSeqNo loadDocIdAndSeqNo(IndexReader reader, Term term) thr
             }
             if (result.isLive) {
                 // The live document must always be the latest copy, thus we can early terminate here.
+                assert latest == null || latest.seqNo <= result.seqNo :
+                    "the live doc does not have the highest seq_no; live_seq_no=" + result.seqNo + " < deleted_seq_no=" + latest.seqNo;
                 return result;
             }
             if (latest == null || latest.seqNo < result.seqNo) {