senvey/Database-Management-System — comment on commit 361e8dd9a8a83f4048bbed5bbc9c93c0affaad1a
File: qe/qe.cc line 479
By senvey:

I recommend you keep left_attr_data for a while (as a field of the class), too. It acts similarly as `this->left_data`. If candidates for join in the right relation is of a large number, this can be particularly effective.