DB2 Tablespace Types

Enhanced Definition

DB2 tablespace types define how data for one or more tables is physically stored and organized within a DB2 database on z/OS. They determine characteristics like data partitioning, storage allocation, recovery granularity, and concurrency, significantly impacting performance, availability, and manageability.

Key Characteristics

- Universal Table Spaces (UTS): The modern and recommended type, offering superior manageability, availability, and performance. UTS are either Partition-by-Growth (PBG) or Partition-by-Range (PBR).
- Partition-by-Growth (PBG UTS): Automatically adds new partitions as data grows, simplifying administration for tables that grow unpredictably. Each partition is a separate data set.
- Partition-by-Range (PBR UTS): Partitions are explicitly defined by user-specified data ranges, allowing for independent management and parallel processing. Can be hash-organized for even data distribution.
- Partitioned Table Spaces (non-UTS): Older type where data for a single table is divided into partitions based on a partitioning key. Each partition can be managed (e.g., reorganized, recovered) independently.
- Segmented Table Spaces (non-UTS): An older type designed for better space reuse and scan performance compared to simple tablespaces. Data is stored in segments, where each segment belongs to only one table.
- Simple Table Spaces (non-UTS): The oldest and least efficient type, allowing multiple tables to share pages within the same tablespace. Highly discouraged due to poor performance, concurrency issues, and lack of features.

Use Cases

- PBG UTS: Ideal for tables with unpredictable growth, high insert rates, or when administrative simplicity is paramount. Often used for audit trails, log tables, or rapidly growing transactional data.
- PBR UTS: Best for very large tables where data can be logically divided by a key (e.g., date, region, customer ID). Facilitates parallel processing for queries and maintenance, and allows for rolling out/in data.
- Partitioned Table Spaces (non-UTS): Primarily found in legacy applications where migration to UTS has not yet occurred. Used for large tables requiring independent management of data subsets.
- Segmented Table Spaces (non-UTS): Also largely superseded by UTS, but might be encountered in older systems for smaller to medium-sized tables with high insert/delete activity where space reuse was a concern.

Related Concepts

Tablespaces are contained within a DB2 database and hold one or more tables. They are typically associated with a storage group that defines the underlying VSAM data sets (or SMS-managed data sets) where the data resides. The choice of tablespace type influences how buffer pools are utilized, affecting I/O performance. Furthermore, tablespace types directly impact the granularity of utility operations (e.g., REORG, RECOVER, COPY) and the effectiveness of data sharing in a data sharing group.

Best Practices:

Standardize on Universal Table Spaces (UTS): For all new application development and whenever possible for existing applications, use PBG or PBR UTS due to their superior manageability, availability, and performance characteristics.
Migrate Legacy Tablespaces: Plan and execute migrations from older segmented or partitioned tablespaces to UTS to leverage modern DB2 features and improve operational efficiency.
Choose Wisely between PBG and PBR: For UTS, select PBG for tables with unpredictable growth or where partitioning key definition is challenging. Opt for PBR when data can be logically partitioned, enabling better parallel processing and data lifecycle management.
Monitor and Tune: Regularly monitor tablespace growth, I/O activity, and utility performance. Adjust partitioning keys, buffer pool assignments, and other parameters as needed to ensure optimal performance.
Consider Data Sharing Implications: When operating in a DB2 data sharing environment, UTS provide better concurrency and reduced contention compared to older tablespace types, especially for online reorganization.