Understanding InnoDB Buffers: Buffer Pool, Change Buffer, Log Buffer, and Doublewrite Buffer

MySQL InnoDB uses several buffers to reduce disk I/O and protect data integrity.

Buffer Pool is an in‑memory cache for table and index pages. It stores pages (default 16 KB) and uses a modified LRU algorithm that separates pages into an old sublist (≈3/8) and a new sublist, with a 1‑second window to avoid evicting hot pages during large scans.

Change Buffer records modifications to secondary index pages that are not currently in the buffer pool, allowing the changes to be applied later when the page is loaded, thus avoiding costly random I/O. It works only for non‑unique secondary indexes.

Log Buffer buffers redo‑log records before they are flushed to the redo‑log file. It batches writes, reducing system‑call overhead, and is flushed based on transaction commit, buffer size, or a periodic 1‑second background thread, controlled by innodb_flush_log_at_trx_commit .

Doublewrite Buffer protects against partial page writes. InnoDB first copies a page to the doublewrite buffer and writes it sequentially to disk; the page is then written to its final location. If a crash occurs, the doublewrite files can be used to recover corrupted pages.

The article also notes configuration considerations, such as the size of the buffer pool, the innodb_old_blocks_pct parameter, and when to disable the change buffer if the workload or hardware makes it unnecessary.

References: MySQL 8.0 InnoDB Storage Engine documentation.