I am experiencing problems with mysql CPU usage after a sharp increase in online users last night. The average server load was 150 (1 min) and the mysql CPU usage in top was 3500-4000%. The show processlist; result was 250 queries. Here is some settings and statuses:

```
max_connections=400
query_cache_type=1
join_buffer_size=4096
query_cache_size=5M
query_cache_limit=1048576
query_cache_min_res_unit=4096

```

Here is the execution of the 

```
show status like '%qcach%';

```

3 times in 30 seconds

```
+-------------------------+------------+
| Variable_name           | Value      |
+-------------------------+------------+
| Qcache_free_blocks      | 597        |
| Qcache_free_memory      | 1658184    |
| Qcache_hits             | 1813237610 |
| Qcache_inserts          | 456473072  |
| Qcache_lowmem_prunes    | 433310255  |
| Qcache_not_cached       | 105476947  |
| Qcache_queries_in_cache | 1564       |
| Qcache_total_blocks     | 4027       |
+-------------------------+------------+
+-------------------------+------------+
| Variable_name           | Value      |
+-------------------------+------------+
| Qcache_free_blocks      | 429        |
| Qcache_free_memory      | 1422288    |
| Qcache_hits             | 1813245095 |
| Qcache_inserts          | 456475419  |
| Qcache_lowmem_prunes    | 433312602  |
| Qcache_not_cached       | 105477523  |
| Qcache_queries_in_cache | 1553       |
| Qcache_total_blocks     | 3896       |
+-------------------------+------------+
+-------------------------+------------+
| Variable_name           | Value      |
+-------------------------+------------+
| Qcache_free_blocks      | 481        |
| Qcache_free_memory      | 1546088    |
| Qcache_hits             | 1813254695 |
| Qcache_inserts          | 456477824  |
| Qcache_lowmem_prunes    | 433314721  |
| Qcache_not_cached       | 105478263  |
| Qcache_queries_in_cache | 1699       |
| Qcache_total_blocks     | 4146       |
+-------------------------+------------+

```

Server configuration: 

```
2 x Intel(R) Xeon(R) CPU E5-2650 v4 @ 2.20GHz.
64GB RAM
Mysql running on SSDs.

```