This directive allows you to tune the tradeoff between increased memory usage and longer searching times. Squid calculates the number of hash table buckets, depending on this directive, the average object size, and the total cache size. Squid’s goal is to have this many objects in each bucket of the hash table.
A larger value here leads to reduced memory usage but longer search times. Conversely, a smaller value leads to faster search times, at the expense of increased memory usage.