How to improve the performance of read ?

[zjizhi zeng]

when i used mysql ad the keystoneis backend in openstack ,i found that the big token table saved 29 millions record and have 4 new token save per seconds. That result to the slow query of a token .since of inserting new token frequently,how could i set the configure to speed up the query operation.
here is some status data :
+-----------------------+-------------+
| Variable_name | Value |
+-----------------------+-------------+
| Handler_read_first | 259573419 |
| Handler_read_key | 1344821219 |
| Handler_read_next | 3908969530 |
| Handler_read_prev | 1235 |
| Handler_read_rnd | 1951101 |
| Handler_read_rnd_next | 48777237518 |
+-----------------------+-------------+

and
+-------------------------+------------+
| Variable_name | Value |
+-------------------------+------------+
| Qcache_free_blocks | 498 |
| Qcache_free_memory | 1192512 |
| Qcache_hits | 1122242834 |
| Qcache_inserts | 352700155 |
| Qcache_lowmem_prunes | 34145019 |
| Qcache_not_cached | 1529123943 |
| Qcache_queries_in_cache | 1681 |
| Qcache_total_blocks | 4949 |
+-------------------------+------------+

please give me some help.thanks.