解析 policy used to size sql working areas (manual/auto)

SQL working areas, also known as SQL buffer pools or cache, are memory regions used by database management systems (DBMS) to store the results of recently executed queries and other frequently accessed data. The sizing of these working areas can significantly impact the performance of an SQL server. There are two primary methods for managing this: manual and automatic. 1. Manual Policy: In a manual policy, the database administrator (DBA) has direct control over configuring the SQL working area size. This approach typically involves: - Setting explicit limits: The DBA may set specific sizes for buffers, such as read-ahead buffers, sort buffers, or temporary tablespace. They might decide on the total amount of memory to allocate for these purposes. - Buffer Pool Configuration: Some DBMS allow adjusting parameters like `pga_aggregate_target`, `db_buffer_cache_size`, or `large_pool_size` to control the overall buffer pool size. - Monitoring and Tuning: DBAs periodically monitor the usage of these areas, adjust settings based on workload patterns, and make sure they don't run out of memory, which could lead to performance degradation. The benefits of a manual policy are that it allows for precise control and can be tailored to the specific needs of the system. However, it requires a deep understanding of the workload and the DBMS, and frequent tuning may be necessary. 2. Automatic Policy (Automatic Memory Management, or AMM): Modern DBMS like Oracle's Automatic Workload Repository (AWR) or SQL Server's Adaptive Memory feature employ an automatic memory management policy. These systems: - Dynamic Allocation: They automatically allocate memory to different SQL working areas based on the current workload demands. This means the system learns from query execution patterns and adjusts the allocation accordingly. - Memory Tracking: They track the usage of SQL buffers and release unused space when needed, reducing the need for manual tuning. - Memory Sizing Algorithms: They use sophisticated algorithms to determine the optimal size for each buffer type based on factors like query complexity, data access patterns, and available system resources. The advantage of an automatic policy is that it relieves the DBA from constant monitoring and tuning. However, it may not always provide the same level of control as a manual policy, and it relies on the underlying algorithms to make good decisions, which may not always be perfect. In summary, the choice between manual and automatic policies for sizing SQL working areas depends on the organization's preference, expertise, and the complexity of their workload. A manual policy provides more control but requires ongoing attention, while an automatic policy offers less hands-on management but may require less expert knowledge. [2024-05-13 10:55:58 | AI写代码神器 | 530点数解答]