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mysql> show variables like '%query_cache%';                       
+------------------------------+-----------+
| Variable_name                | Value     |
+------------------------------+-----------+
| have_query_cache             | YES       |
| query_cache_limit            | 1048576   |
| query_cache_min_res_unit     | 4096      |
| query_cache_size             | 536870912 |
| query_cache_type             | ON        |
| query_cache_wlock_invalidate | OFF       |
+------------------------------+-----------+

mysql> show status like '%Qcache%';                                            
+-------------------------+-----------+
| Variable_name           | Value     |
+-------------------------+-----------+
| Qcache_free_blocks      | 9939      |
| Qcache_free_memory      | 480086640 |
| Qcache_hits             | 65276811 |
| Qcache_inserts          | 41509403 |
| Qcache_lowmem_prunes    | 0         |
| Qcache_not_cached       | 2065484   |
| Qcache_queries_in_cache | 22970     |
| Qcache_total_blocks     | 56252     |
+-------------------------+-----------+
最关键的参数是Qcache_lowmem_prunes ,如果它是一个非0的参数,那么说明服务器运行不正常,会有缓存被排除

mysql> show status like 'Com_sel%';                                          
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| Com_select    | 1     |
+---------------+-------+

如果发现不正常只需要修改/etc/my.cnf中的
query_cache_size = 512M
加大cache size即可解决
最后别忘记重启数据库.