Hello Sergei, Please review a patch for MDEV-13790. It removes the attempt to search the best suitable buffer and just returns the result in "str" passed to val_str(). I'm quite sure this optimization gives nothing. In can be useful only under very rare conditions, but generates so many bugs. Moreover, in 10.3 (or 10.4) we'll work on reentrant items. So all Item_xxx::tmp_buffer will be gone anyway, together with this optimization. I think an optimization proposal. Why not to introduce a new method: class Item { public: .. virtual append_to_string(String *str); .. } So for example Field_varchar could write directly to "str" passed to Item_func_concat::val_str(). This will make sure that the first allocation is done on the target "str", and "str" will always be the best buffer instead of any Item_xxx::tmp_value. Thanks!