Shrink slog reserved space to 4GB

src/storage/slog/ob_storage_logger_manager.h

@@ -71,7 +71,7 @@ private:
 
 private:
   static constexpr int64_t NORMAL_LOG_ITEM_SIZE = 512 * 1024; //512KB
-  static constexpr int64_t RESERVED_DISK_SIZE = 10 * 1024 * 1024 * 1024L; // 10G
+  static constexpr int64_t RESERVED_DISK_SIZE = 4 * 1024 * 1024 * 1024L; // 4G
 
   common::ObArenaAllocator allocator_;
   const char *log_dir_;