MySQL Caching and the InnoDB Buffer Pool Explained

Disk is slow; memory is fast. The InnoDB buffer pool caches table and index pages in RAM so repeated reads never touch the disk — it's the engine room of MySQL performance.

Key Points

• The buffer pool holds recently used data and index pages in memory
• Warm cache: the second run of a heavy query is often 10–100× faster
• The old query cache was removed in MySQL 8.0 — it hurt concurrency
• Size it with innodb_buffer_pool_size; monitor hit rate via SHOW ENGINE INNODB STATUS
• Application-level caching (Redis) complements, not replaces, the buffer pool
• Sudden slowness after restart? The cache is cold — it needs warming up