Merge branch 'branch-0.3.1' into 'branch-0.3.1'

MS-330 Stability test failed caused by server core dumped

See merge request megasearch/milvus!331

Former-commit-id: 6bc84abf296104fa0d75f451f7dc4da4f781d540

cpp/src/db/DBImpl.cpp

@@ -482,7 +482,7 @@ void DBImpl::BackgroundCompaction(std::set<std::string> table_ids) {
 
     meta_ptr_->Archive();
 
-    int ttl = 1;
+    int ttl = 5*meta::M_SEC;//default: file will be deleted after 5 minutes
     if (options_.mode == Options::MODE::CLUSTER) {
         ttl = meta::D_SEC;
     }