MS-404 Release index after search task done avoid memory increment continues

Former-commit-id: ec8adebf07cd960777ea053ecdeaed06dae50a5b

cpp/CHANGELOG.md

@@ -40,6 +40,7 @@ Please mark all change in change log and use the ticket from JIRA.
 - MS-394 - Update scheduler unittest
 - MS-400 - Add timestamp record in task state change function
 - MS-402 - Add dump implementation for TaskTableItem
+- MS-404 - Release index after search task done avoid memory increment continues
 
 ## New Feature
 - MS-343 - Implement ResourceMgr

cpp/src/scheduler/task/SearchTask.cpp

@@ -207,6 +207,9 @@ XSearchTask::Execute() {
     CollectDurationMetrics(index_type_, total_time);
 
     rc.ElapseFromBegin("totally cost");
+
+    // release index in resource
+    index_engine_ = nullptr;
 }
 
 TaskPtr