This gem makes updating specified number fields by ActiveRecord in unusual way. Instead of generating sql script to update value in usual way like this: UPDATE users SET money = 10 WHERE id = 1; It replaces it with UPDATE users SET money = money + delta WHERE id = 1; where delta is difference between old value and new value of that field. This solves problem with simultaneous updating of the same field by different threads (problem known as race condition). Source code: https://github.com/izbor/delta_attributes