mysql 禁用查詢緩存 query cache

os:centos 6.8
mysql: 5.5.49

MySQL Query Cache 會緩存select 查詢，但是在調優sql查詢及測試數據庫的性能時需要禁用該功能。

查看變量、狀態

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)

注意參數 query_cache_size、query_cache_type

臨時會話修改

mysql> set query_cache_type=0;

臨時全局修改

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

還有一種方式是添加類似oracle的hint

select sql_no_cache count(*) from mysql.user; 

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

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