Support ordered segment list in trace query (#3906)

* Sort the segment fragments

* Add comment.

* Remove unnecessary box codes.

oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/query/TraceQueryService.java

@@ -19,22 +19,38 @@
 package org.apache.skywalking.oap.server.core.query;
 
 import java.io.IOException;
-import java.util.*;
-import org.apache.skywalking.apm.network.language.agent.*;
-import org.apache.skywalking.apm.network.language.agent.v2.*;
-import org.apache.skywalking.oap.server.core.*;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.LinkedList;
+import java.util.List;
+import org.apache.skywalking.apm.network.language.agent.SpanObject;
+import org.apache.skywalking.apm.network.language.agent.TraceSegmentObject;
+import org.apache.skywalking.apm.network.language.agent.UniqueId;
+import org.apache.skywalking.apm.network.language.agent.v2.SegmentObject;
+import org.apache.skywalking.apm.network.language.agent.v2.SpanObjectV2;
+import org.apache.skywalking.oap.server.core.Const;
+import org.apache.skywalking.oap.server.core.CoreModule;
 import org.apache.skywalking.oap.server.core.analysis.manual.segment.SegmentRecord;
-import org.apache.skywalking.oap.server.core.cache.*;
+import org.apache.skywalking.oap.server.core.cache.EndpointInventoryCache;
+import org.apache.skywalking.oap.server.core.cache.NetworkAddressInventoryCache;
+import org.apache.skywalking.oap.server.core.cache.ServiceInventoryCache;
 import org.apache.skywalking.oap.server.core.config.IComponentLibraryCatalogService;
+import org.apache.skywalking.oap.server.core.query.entity.KeyValue;
+import org.apache.skywalking.oap.server.core.query.entity.LogEntity;
+import org.apache.skywalking.oap.server.core.query.entity.Pagination;
+import org.apache.skywalking.oap.server.core.query.entity.QueryOrder;
+import org.apache.skywalking.oap.server.core.query.entity.Ref;
 import org.apache.skywalking.oap.server.core.query.entity.RefType;
+import org.apache.skywalking.oap.server.core.query.entity.Span;
 import org.apache.skywalking.oap.server.core.query.entity.Trace;
-import org.apache.skywalking.oap.server.core.query.entity.*;
+import org.apache.skywalking.oap.server.core.query.entity.TraceBrief;
+import org.apache.skywalking.oap.server.core.query.entity.TraceState;
 import org.apache.skywalking.oap.server.core.register.EndpointInventory;
 import org.apache.skywalking.oap.server.core.register.ServiceInventory;
 import org.apache.skywalking.oap.server.core.storage.StorageModule;
 import org.apache.skywalking.oap.server.core.storage.query.ITraceQueryDAO;
+import org.apache.skywalking.oap.server.library.module.ModuleManager;
 import org.apache.skywalking.oap.server.library.module.Service;
-import org.apache.skywalking.oap.server.library.module.*;
 import org.apache.skywalking.oap.server.library.util.CollectionUtils;
 
 import static java.util.Objects.nonNull;
@@ -374,6 +390,14 @@ public class TraceQueryService implements Service {
                 rootSpans.add(span);
             }
         });
+        /**
+         * In some cases, there are segment fragments, which could not be linked by Ref,
+         * because of two kinds of reasons.
+         * 1. Multiple leaf segments have no particular order in the storage.
+         * 2. Lost in sampling, agent fail safe, segment lost, even bug.
+         * Sorting the segments makes the trace view more readable.
+         */
+        rootSpans.sort(Comparator.comparing(span -> span.getStartTime()));
         return rootSpans;
     }