[inner-2371] fix: sql execution hang problem caused by the inability to respond to the front side due to unprocessed packets.

(cherry picked from commit dcff228b4c13bf0fd9f7bb0d52f9c18aaba36b59、07c0c1f1c986a71fb74d0fcc0379965592c63b49)

src/main/java/com/actiontech/dble/services/BackendService.java

@@ -130,7 +130,7 @@ public abstract class BackendService extends AbstractService {
             handleDataError(e);
         } finally {
             isHandling.set(false);
-            if (taskQueue.size() > 0) {
+            if (!taskQueue.isEmpty()) {
                 doHandle(task);
             }
         }
@@ -222,7 +222,7 @@ public abstract class BackendService extends AbstractService {
     protected void handleDataError(Exception e) {
         LOGGER.warn(this.toString() + " handle data error:", e);
         connection.close("handle data error:" + e.getMessage());
-        while (taskQueue.size() > 0) {
+        while (!taskQueue.isEmpty()) {
             clearTaskQueue();
             readSize.set(0);
             // clear all data from the client
@@ -649,8 +649,8 @@ public abstract class BackendService extends AbstractService {
                 handleDataError(e);
             } finally {
                 isHandling.set(false);
-                if (taskQueue.size() > 0) {
-                    doHandle(null);
+                if (!taskQueue.isEmpty()) {
+                    doHandle(taskQueue.peek());
                 }
             }
         }

src/main/java/com/actiontech/dble/services/mysqlsharding/MySQLResponseService.java

@@ -509,7 +509,7 @@ public class MySQLResponseService extends BackendService {
     @Override
     protected Executor getExecutor() {
         Executor executor;
-        if (complexQuery) {
+        if (complexQuery || SystemConfig.getInstance().getUsePerformanceMode() == 1) {
             executor = DbleServer.getInstance().getComplexQueryExecutor();
         } else {
             executor = DbleServer.getInstance().getBackendBusinessExecutor();