[CP] avoid ddl task spin

src/rootserver/ddl_task/ob_ddl_scheduler.cpp

@@ -924,7 +924,7 @@ void ObDDLScheduler::run1()
       }
       if (do_idle) {
         first_retry_task = nullptr;
-        idler_.idle(10 * 1000L);
+        idler_.idle(ObDDLTask::DEFAULT_TASK_IDLE_TIME_US);
       }
     }
   }

src/rootserver/ddl_task/ob_ddl_task.cpp

@@ -1114,6 +1114,7 @@ int ObDDLTask::switch_status(const ObDDLTaskStatus new_status, const bool enable
     if (OB_SUCC(ret) && old_status != real_new_status) {
       add_event_info(real_new_status, dst_tenant_id_);
       task_status_ = real_new_status;
+      next_schedule_ts_ = 0; // when status changed, schedule immediately
       LOG_INFO("ddl_scheduler switch status", K(ret), "ddl_event_info", ObDDLEventInfo(), K(task_status_));
     }
 
@@ -1458,6 +1459,11 @@ void ObDDLTask::calc_next_schedule_ts(const int ret_code, const int64_t total_ta
     next_schedule_ts_ = ObTimeUtility::current_time() + ObRandom::rand(min_dt, max_dt);
   } else {
     delay_schedule_time_ = 0;
+    if (next_schedule_ts_ > 0) {
+      // if next_schedule_ts_ is set, means that the task is not to schedule immediately.
+      // make sure it will be delayed at least 10ms to awoid spin
+      next_schedule_ts_ = max(next_schedule_ts_, ObTimeUtility::current_time() + DEFAULT_TASK_IDLE_TIME_US);
+    }
   }
   return;
 }

src/rootserver/ddl_task/ob_ddl_task.h

@@ -578,6 +578,7 @@ public:
       K_(next_schedule_ts), K_(delay_schedule_time), K(execution_id_), K(sql_exec_addr_), K_(data_format_version), K(consumer_group_id_),
       K_(dst_tenant_id), K_(dst_schema_version));
   static const int64_t MAX_ERR_TOLERANCE_CNT = 3L; // Max torlerance count for error code.
+  static const int64_t DEFAULT_TASK_IDLE_TIME_US = 10L * 1000L; // 10ms
 protected:
   int gather_redefinition_stats(const uint64_t tenant_id,
                                 const int64_t task_id,