Better

src/Common/RingBuffer.h

@@ -36,7 +36,7 @@ public:
         if (count == capacity) {
             return false;
         }
-        buffer[advance(count)] = element;
+        buffer[advance(count)] = std::move(element);
         ++count;
         return true;
     }

src/Storages/MergeTree/MergeMutateExecutor.h

@@ -112,7 +112,7 @@ private:
             pending.resize(new_max_tasks_count);
             active.resize(new_max_tasks_count);
 
-            pool.setMaxFreeThreads(0);
+            pool.setMaxFreeThreads(new_threads_count);
             pool.setMaxThreads(new_threads_count);
             pool.setQueueSize(new_max_tasks_count);
         }