Figure 6-8. Given nonrandom numbers, a simple modulus hash function is not likely to produce an even distribution, but more like what this figure shows. This graph is based on 1,000 inputs, the first 500 between 0 and 5, and the remaining 500 between 0 and 1,000.

When Oracle is searching for a buffer, the hash value is created based on a combination of the block's file number and block number, which is known as the data block address (DBA). So the hash function essentially hashes on the buffer's file number and block number. It is a very convenient situation and allows for a very quick hash.

Hash value inputs are hashed to buckets. Every output value represents a single bucket. For example, because the modulus 10 hash function shown in Figure 6-6 can produce ten possible output values, there will be ten hash buckets. If the input value were 9, then it would be hashed to bucket number nine. It's that simple.