mysql 禁用查询缓存 query cache

os:centos 6.8
mysql: 5.5.49

MySQL Query Cache 会缓存select 查询，但是在调优sql查询及测试数据库的性能时需要禁用该功能。

查看变量、状态

mysql> show global variables like '%cache%'; +------------------------------+----------------------+
| Variable_name | Value | +------------------------------+----------------------+
| binlog_cache_size            | 8388608              |
| binlog_stmt_cache_size | 32768 | | have_query_cache | YES | | key_cache_age_threshold      | 300                  |
| key_cache_block_size | 1024 | | key_cache_division_limit     | 100                  |
| max_binlog_cache_size | 536870912 | | max_binlog_stmt_cache_size | 18446744073709547520 | | metadata_locks_cache_size    | 1024                 |
| query_cache_limit            | 4194304              |
| query_cache_min_res_unit     | 4096                 |
| query_cache_size             | 134217728            |
| query_cache_type             | ON                   |
| query_cache_wlock_invalidate | OFF | | stored_program_cache | 256 | | table_definition_cache | 400 | | table_open_cache | 400 | | thread_cache_size | 16 | +------------------------------+----------------------+ 18 rows in set (0.00 sec) mysql> show global status like '%cache%hit%'; +-------------------------+--------+
| Variable_name | Value | +-------------------------+--------+
| Qcache_hits | 552743 | | Ssl_callback_cache_hits | 0      |
| Ssl_session_cache_hits | 0 | +-------------------------+--------+
3 rows in set (0.00 sec)

注意参数 query_cache_size、query_cache_type

临时会话修改

mysql> set query_cache_type=0;

临时全局修改

mysql> set global query_cache_size=0;
mysql> set global query_cache_type=0;

永久修改

# vi my.cnf
query_cache_type=0
query_cache_size=0

还有一种方式是添加类似oracle的hint

select sql_no_cache count(*) from mysql.user; 

mysql 5.5 文档上描述
Note
Query cache was deprecated in MySQL 5.7 and removed in MySQL 8.0 (and later).

参考:
https://dev.mysql.com/doc/refman/5.5/en/mysql-installer-workflow.html