buffertpool

Buffertpool, also known as buffer pool, is a region of main memory allocated by a database management system (DBMS) or operating system to cache data that has been read from, or will soon be written to, storage devices. By keeping hot data in memory, the pool reduces disk I/O and speeds up query processing. The data held in a buffer pool is organized into fixed-size pages (for example 8 KB).

In a DBMS, the buffer pool stores table data, index blocks, and other metadata. When a page is requested, the system first checks the pool; if present, the operation is served from memory (a cache hit). If not, the page is read from disk into the pool, possibly evicting another page according to a replacement policy.

Replacement policy and writeback: Most systems use variations of LRU (least recently used) with aging, or multi-tiered schemes that prioritize frequently accessed pages. Dirty pages are periodically written back to storage by background processes or during checkpoints to ensure durability.

Tuning and metrics: The pool size is a major tuning knob; insufficient size leads to I/O bottlenecks, while excess memory competes with the OS and other processes. Monitoring metrics include cache hit ratio, read/write I/O, and pages evicted. Warm-up and workload patterns affect performance.

Variants: In MySQL and InnoDB the buffer pool is a central feature; SQL Server uses a buffer pool in the memory manager; PostgreSQL uses shared_buffers and OS cache; Oracle uses the buffer cache in the System Global Area. Some systems support extending the buffer pool with fast storage.