Syntax:
LOAD INDEX INTO CACHE
  tbl_index_list [, tbl_index_list] ...

tbl_index_list:
  tbl_name
    [[INDEX|KEY] (index_name[, index_name] ...)]
    [IGNORE LEAVES]

The LOAD INDEX INTO CACHE statement preloads a table index into the key
cache to which it has been assigned by an explicit CACHE INDEX
statement, or into the default key cache otherwise. LOAD INDEX INTO
CACHE is used only for MyISAM tables. It is not supported for tables
having user-defined partitioning (see
http://dev.mysql.com/doc/refman/5.1/en/partitioning-limitations.html.)

The IGNORE LEAVES modifier causes only blocks for the non-leaf nodes of
the index to be preloaded.

URL: http://dev.mysql.com/doc/refman/5.1/en/load-index.html

