MySQL in a Nutshell, 2nd Edition

Name

LOAD INDEX INTO CACHE

Synopsis

LOAD INDEX INTO CACHE
  table [[INDEX|KEY] (index[, ...)] [IGNORE LEAVES]
  [, ...]

Use this statement to preload a table’s index into a given key cache for a MyISAM table. The syntax allows one or more indexes to be specified in a comma-separated list in parentheses, in order to preload just the specified indexes, but presently MySQL simply loads all the indexes for the table into the cache. The keywords INDEX and KEY are interchangeable and optional; they do not affect the results. The IGNORE LEAVES clause instructs MySQL not to preload leaf nodes of the index. Here is an example of how you can use this statement:

LOAD INDEX INTO CACHE workreq;

+----------------------+--------------+----------+----------+
| Table                | Op           | Msg_type | Msg_text |
+----------------------+--------------+----------+----------+
| workrequests.workreq | preload_keys | status   | OK       |
+----------------------+--------------+----------+----------+