MyISAM indexes are cached in a data structure called the key cache or (less frequently) key buffer. This cache should greatly reduce access to the physical index files. The cached indexes can also be modified in memory; only later will the changes be flushed to the disk.
The key cache can be disabled. Data does not have a special cache within MariaDB. Thus, the operating system cache mechanisms are used instead. The same happens with data if the key cache is disabled.
If we mainly use MyISAM tables, the key cache should be very big. If we do not use MyISAM, the key cache can be set to the minimum value, which is
8 (for example, to free the memory for the InnoDB buffer pool). It is not possible to completely disable it. However, ...