Balanced Allocations Yossi Azar \Lambda Andrei Z. Broder y Anna R. Karlin z Eli Upfal x Summary: Balanced Allocations Yossi Azar \Lambda Andrei Z. Broder y Anna R. Karlin z Eli Upfal x Abstract Suppose that we sequentially place n balls into n boxes by putting each ball into a randomly chosen box. It is well known that when we are done, the fullest box has with high probability (1 + o(1)) ln n= ln ln n balls in it. Suppose instead, that for each ball we choose two boxes at random and place the ball into the one which is less full at the time of placement. We show that with high probability, the fullest box contains only ln ln n= ln 2+O(1) balls -- exponentially less than before. Furthermore, we show that a similar gap exists in the infinite process, where at each step one ball, chosen uniformly at random, is deleted, and one ball is added in the manner above. We discuss consequences of this and related theorems for dynamic resource allocation, hashing, and on­line load balancing. 1 Introduction Suppose that we sequentially place n balls into n boxes by putting each ball into a randomly chosen box. Properties of this random allocation process have been extensively studied in the probability and statistics literature. Collections: Computer Technologies and Information Sciences