bufferpool

A bufferpool (often written as buffer pool) is a reserved region of main memory used to cache blocks of data that are stored on slower storage such as disk. The goal is to reduce disk I/O and lower access latency by serving many read and write requests from memory rather than from storage. While commonly associated with database management systems, the concept also appears in operating system subsystems and other storage-oriented software.

A bufferpool is typically organized into fixed-size frames or pages, each capable of holding a data block identified by a block address. The pool maintains metadata for each cached block, including the block identifier, a dirty flag indicating whether the block has been modified, and a pin count showing how many operations are currently using the block. On a read, the system looks for the block in the pool; a hit returns the data from memory, while a miss loads the block from storage into the pool, possibly evicting another block to make room. On a write, the block may be updated in memory and marked dirty; the system eventually writes dirty blocks back to storage, either in a write-back fashion asynchronously or via a write-through approach during commit or checkpoint events.

Replacement policies (such as LRU, clock, or more advanced algorithms) determine which blocks to evict. Additional techniques include read-ahead to prefetch likely-needed blocks and pinning to prevent eviction during active use. The size and management of a bufferpool are critical for performance: too small a pool increases misses and I/O; too large a pool wastes memory.

Examples include database systems like MySQL InnoDB, which uses an InnoDB Buffer Pool to cache data and index pages, and various OS-level or storage engines that implement similar caching layers.