#### 8.10.2.5 Key Cache Block Size

 It is possible to specify the size of the block buffers for an individual key cache using the [`key_cache_block_size`](server-system-variables.html#sysvar_key_cache_block_size) variable. This permits tuning of the performance of I/O operations for index files.

 The best performance for I/O operations is achieved when the size of read buffers is equal to the size of the native operating system I/O buffers. But setting the size of key nodes equal to the size of the I/O buffer does not always ensure the best overall performance. When reading the big leaf nodes, the server pulls in a lot of unnecessary data, effectively preventing reading other leaf nodes.

 To control the size of blocks in the `.MYI` index file of `MyISAM` tables, use the [`--myisam-block-size`](server-options.html#option_mysqld_myisam-block-size) option at server startup.

