Key Range - Span of keys

Key Characteristics

• • Contiguous Values: A key range always represents an unbroken sequence of key values, from a starting key to an ending key, defining a specific segment of data.
  • Data Partitioning: It is a primary mechanism for partitioning large data sets (e.g., VSAM KSDS) or database tables/segments (e.g., DB2, IMS) into smaller, more manageable units.
  • Access Efficiency: By directing I/O operations to specific key ranges, access time can be significantly reduced, especially for batch processing or targeted queries, as the system only needs to search a subset of data.
  • Load Balancing: Key ranges are crucial for distributing data across multiple storage volumes or even different physical devices, aiding in workload balancing and reducing contention.
  • Dynamic Definition: In systems like DB2, key ranges for partitions can often be defined or altered, allowing for flexible data growth, archiving, and management without affecting the entire table.
  • Boundary Keys: Each key range is defined by a low key (inclusive) and a high key (inclusive or exclusive, depending on the system), which act as boundaries for the data contained within that range.

Use Cases

• • VSAM KSDS Partitioning: Defining specific key ranges for different components of a large VSAM KSDS to distribute data across multiple volumes or for easier backup/recovery of subsets.
  • DB2 Table Partitioning: Dividing a large DB2 table into partitions based on key ranges (e.g., date ranges for historical data) to improve query performance, simplify maintenance, and enable rolling window operations.
  • IMS Database Segmentation: In IMS, defining key ranges for secondary indexes or for partitioning databases (e.g., using DBRC for data set groups) to manage large hierarchical structures more effectively.
  • Batch Processing Optimization: Processing only a specific key range of a file or database in a batch job to reduce processing time and resource consumption, often specified in SELECT statements or utility control cards.
  • Data Archiving/Purging: Identifying and processing data records within a specific key range for archiving older data or purging obsolete records without affecting the entire dataset.

Related Concepts