Cache tables

If you’re using open addressing-class schemes, you then have a rule to find other array indices that a value with the given hash code might be found at; with separate chaining, your array entries point to the head of a linked list, or the root of a binary tree, or whatever other data structure you prefer for the given use case. That makes the most natural representation a simple 2D array: N rows of hash buckets with P columns, each with space for one entry, forming a N×P grid. One of the benefits of keeping P entries per row is that it allows us to have two different keys with identical hash values (i.e. a hash collision) in the same table; as per the birthday problem, even with a well-distributed hash, you are likely to see collisions.

Source: fgiesen.wordpress.com