Merge branch 'branch-0.4.0' into fix_MS493

Former-commit-id: 59a9f1966eca287932406ece6e57c0485eed2d0c

cpp/CHANGELOG.md

@@ -26,6 +26,7 @@ Please mark all change in change log and use the ticket from JIRA.
 - MS-467 - mysql db test failed
 - MS-470 - Drop index success, which table not created
 - MS-471 - code coverage run failed
+- MS-492 - Drop index failed if index have been created with index_type: FLAT
 - MS-493 - Knowhere unittest crash
 
 ## Improvement

cpp/src/server/grpc_impl/GrpcRequestTask.cpp

@@ -955,15 +955,8 @@ DropIndexTask::OnExecute() {
             return SetError(res, "Invalid table name: " + table_name_);
         }
 
-        //step 2:check index existence
-        engine::TableIndex index;
-        engine::Status stat = DBWrapper::DB()->DescribeIndex(table_name_, index);
-        if (index.engine_type_ == 1) {
-            return SetError(SERVER_UNEXPECTED_ERROR, "index not existed");
-        }
-
-        //step 3: check table existence
-        stat = DBWrapper::DB()->DropIndex(table_name_);
+        //step 2: check table existence
+        auto stat = DBWrapper::DB()->DropIndex(table_name_);
         if (!stat.ok()) {
             return SetError(DB_META_TRANSACTION_FAILED, stat.ToString());
         }