set alarm record ordered by start time desc. (#3353)

oap-server/server-storage-plugin/storage-elasticsearch-plugin/src/main/java/org/apache/skywalking/oap/server/storage/plugin/elasticsearch/query/AlarmQueryEsDAO.java

@@ -30,6 +30,7 @@ import org.elasticsearch.action.search.SearchResponse;
 import org.elasticsearch.index.query.*;
 import org.elasticsearch.search.SearchHit;
 import org.elasticsearch.search.builder.SearchSourceBuilder;
+import org.elasticsearch.search.sort.SortOrder;
 
 /**
  * @author peng-yongsheng
@@ -57,7 +58,7 @@ public class AlarmQueryEsDAO extends EsDAO implements IAlarmQueryDAO {
             boolQueryBuilder.must().add(QueryBuilders.matchPhraseQuery(matchCName, keyword));
         }
 
-        sourceBuilder.query(boolQueryBuilder);
+        sourceBuilder.query(boolQueryBuilder).sort(AlarmRecord.START_TIME, SortOrder.DESC);
         sourceBuilder.size(limit);
         sourceBuilder.from(from);