MySQL 8 Administrator???s Guide

MyISAM key cache

The MyISAM storage engine incorporates a strategy that is supported by many database management systems to minimize the disk I/O. The cache mechanism is employed by MyISAM to keep the most frequently accessed table blocks in memory as follows:

• A special structure known as a key cache is maintained for index blocks. The most used index blocks are placed in the structure containing a number of block buffers.
• MySQL relies on the native operating system filesystem cache for data blocks.

The key_buffer_size system variable determines the size of the key cache. If it is set to zero, no key cache is used. The key cache is also not used if the key_buffer_size value is too small to allocate the minimum order of block buffers. All ...