Bucket

Key Characteristics

• • Logical Grouping: A bucket represents a logical grouping of storage locations, not necessarily a fixed physical block, though it often maps to one or more physical blocks or control intervals on DASD.
  • Hashing Target: It is the direct result or target address generated by a hashing function, indicating where a record should be stored or retrieved for rapid access.
  • Collision Handling: Buckets are fundamental to collision resolution strategies in hashing. Multiple records that hash to the same bucket are stored within that bucket, often using techniques like chaining or open addressing.
  • Fixed or Variable Capacity: The capacity of a bucket can be fixed (e.g., a specific number of records or bytes) or dynamically managed, depending on the implementation of the access method or database.
  • Performance Impact: The design and size of buckets significantly impact data access performance, as efficient bucket utilization minimizes I/O operations and search times.

Use Cases

• • IMS HDAM Database Organization: In IMS Hierarchical Direct Access Method (HDAM) databases, a hash routine determines the root anchor point (RAP) within a block (often conceptually a bucket) where a root segment and its dependent segments are stored.
  • Custom Hashing Routines: Application programs, particularly those written in COBOL or Assembler, might implement custom hashing routines to quickly locate records in large, directly-accessed datasets, where each hash output points to a specific "bucket" of records.
  • In-memory Data Structures: High-performance in-memory hash tables used by mainframe applications (e.g., for caching frequently accessed data or lookup tables) employ buckets to organize data for fast retrieval.
  • Indexed File Systems (Conceptual): While not explicitly named "buckets," the underlying principles of indexing and distributing data across storage units to minimize search time share conceptual similarities, where an index entry points to a storage subdivision.

Related Concepts