One obvious way to increase the average chain length is to decrease the number of chains, which can be achieved by decreasing the number of hash buckets. Simply decrease the value of instance parameter _db_block_hash_buckets to say, 50, ensure your queried blocks reside in the buffer cache. You would get massive CBC latch contention very quickly. But Oracle will resist your efforts by ensuring there are at least 64 buckets, which is still slow enough to ensure plenty of contention.

Realistically though, one solution to CBC latch contention is to increase the number of hash buckets. While this will decrease the average chain length, if one particular chain is very long and popular, this solution will not improve performance. Furthermore, Oracle creates a large number of chains by default, so it is unlikely that adding chains will create the performance benefit you seek. But it is a valid approach and should be considered.

Although the problem of long chains is very rare, if it does occur, it is very serious indeed. Understanding how this could happen not only helps you solve the problem if it should arise, but also allows a much deeper understanding of the CBCs, latching, undo, and read consistency. It even touches on RAC systems.