Multi-Directory Hashing

We present a new dynamic hashing scheme for disk-based databases, called Multi-Directory Hashing (MDH). MDH uses multiple hash directories to access a file. The size of each hash directory grows dynamically with the file size. The advantages of MDH are enhanced concurrency, improved bucket utilization and smaller total directory size than single-directory hashing. The expected utilization of MDH increases monotonically and approaches 100% as the number of hash directories increases. A variation of MDH, called Main Memory Multi-Directory Hashing (MM-MDH), is also described. MM-MDH achieves optimal search time in main memory databases. The performance of both methods is analyzed through theoretical and experimental results.