LOAD INDEX INTO CACHE tbl_index_list [, tbl_index_list] ... tbl_index_list: tbl_name [[INDEX|KEY] (index_name[, index_name] ...)] [IGNORE LEAVES]
LOAD INDEX INTO CACHE statement preloads a table index into the key
cache to which it has been assigned by an explicit
statement, or into the default key cache otherwise.
LOAD INDEX INTO CACHE is used only for MyISAM or Aria tables.
IGNORE LEAVES modifier causes only blocks for the nonleaf nodes of
the index to be preloaded.