新特性解讀 | MySQL 8.0 輕鬆改配置，雲上友好

作者：陳俊聰

背景

MySQL 5.7 及之前版本下修改配置，如果能動態修改的，可以用 set global 語法，不能動態修改的，只能修改 /etc/my.cnf 配置文件，之後重啓生效。如果需要持久化動態修改的參數，也只能同時修改 /etc/my.cnf 配置文件。

這個對雲上環境不友好，畢竟雲數據庫上，大家無法直接遠程底層虛擬機修改配置文件。針對如何持久化參數配置，在 MySQL 8.0，有一個新特性，可以實現輕鬆修改配置文件，那就是 set persist 和 set persist_only 語法。前者用於修改並持久化動態參數，後者用於持久化靜態參數。

修改並持久化動態參數一例

mysql> show variables like '%innodb_buffer_pool_size%';
+-------------------------+-----------+
| Variable_name           | Value     |
+-------------------------+-----------+
| innodb_buffer_pool_size | 134217728 |
+-------------------------+-----------+
1 row in set (0.01 sec)

mysql> set persist innodb_buffer_pool_size=134217728*2;
Query OK, 0 rows affected (0.00 sec)

mysql> show variables like '%innodb_buffer_pool_size%';
+-------------------------+-----------+
| Variable_name           | Value     |
+-------------------------+-----------+
| innodb_buffer_pool_size | 268435456 |
+-------------------------+-----------+
1 row in set (0.00 sec)

在數據目錄裏，會生成一個持久化參數的 json 格式文件，內容如下：

[root@pxc1 data]# cat mysqld-auto.cnf |jq
{
  "Version": 1,
  "mysql_server": {
    "innodb_buffer_pool_size": {
      "Value": "268435456",
      "Metadata": {
        "Timestamp": 1570678719890919,
        "User": "root",
        "Host": "localhost"
      }
    }
}

點評: 居然有時間戳，還有誰修改了參數！

持久化靜態參數一例

# 我們先模擬沒有權限
mysql> revoke SYSTEM_VARIABLES_ADMIN, PERSIST_RO_VARIABLES_ADMIN on *.* from 'root'@'localhost';
Query OK, 0 rows affected, 1 warning (0.01 sec)

mysql> show variables like 'innodb_log_file_size';
+----------------------+----------+
| Variable_name        | Value    |
+----------------------+----------+
| innodb_log_file_size | 50331648 |
+----------------------+----------+
1 row in set (0.01 sec)

mysql> set persist innodb_log_file_size=50331648*2;
ERROR 1238 (HY000): Variable 'innodb_log_file_size' is a read only variable

# 因缺少SYSTEM_VARIABLES_ADMIN 和 PERSIST_RO_VARIABLES_ADMIN 權限而報錯
mysql> set persist_only innodb_log_file_size=50331648*2;
ERROR 3630 (42000): Access denied; you need SYSTEM_VARIABLES_ADMIN and PERSIST_RO_VARIABLES_ADMIN privileges for this operation

# 增加授權
mysql> grant SYSTEM_VARIABLES_ADMIN, PERSIST_RO_VARIABLES_ADMIN on *.* to 'root'@'localhost';
Query OK, 0 rows affected, 1 warning (0.01 sec)

# 修改成功
mysql> set persist_only innodb_log_file_size=50331648*2;
Query OK, 0 rows affected (0.00 sec)

# 重啓，MySQL8.0支持在數據庫裏重啓操作，雲友好！
mysql> restart;
Query OK, 0 rows affected (0.00 sec)

mysql> restart;
ERROR 3707 (HY000): Restart server failed (mysqld is not managed by supervisor process).

注意: 要求mysqld運行在mysqld_safe下。

清空 persist 持久化參數

mysql> RESET PERSIST;
Query OK, 0 rows affected (0.00 sec)

人手刪除此文件或人手清空此文件內容，也可以達到相同效果。
當然了，雲數據庫上只能用 RESET PERSIST 了。

相關 performance_schema 表

1. 查看數據庫啓動後載入的 PERSIST 相關參數

在重啓數據庫後，我們可以通過表 performance_schema.variables_info 查看我們從哪些 mysqld-auto.cnf 載入了哪些參數。

mysql> select * from performance_schema.variables_info where variable_source like 'PERSISTED'\G
*************************** 1. row ***************************
  VARIABLE_NAME: innodb_buffer_pool_size
VARIABLE_SOURCE: PERSISTED
  VARIABLE_PATH: /data/mysql/mysql3308/data/mysqld-auto.cnf
      MIN_VALUE: 5242880
      MAX_VALUE: 9223372036854775807
       SET_TIME: 2019-10-10 11:38:39.890919
       SET_USER: root
       SET_HOST: localhost
*************************** 2. row ***************************
  VARIABLE_NAME: innodb_log_file_size
VARIABLE_SOURCE: PERSISTED
  VARIABLE_PATH: /data/mysql/mysql3308/data/mysqld-auto.cnf
      MIN_VALUE: 4194304
      MAX_VALUE: 18446744073709551615
       SET_TIME: 2019-10-10 11:21:12.623177
       SET_USER: root
       SET_HOST: localhost
2 rows in set (0.02 sec)

2. 查看變量都來自於哪裏

mysql> SELECT t1.VARIABLE_NAME, VARIABLE_VALUE, VARIABLE_SOURCE
    -> FROM performance_schema.variables_info t1
    -> JOIN performance_schema.global_variables t2
    -> ON t2.VARIABLE_NAME=t1.VARIABLE_NAME
    -> WHERE t1.VARIABLE_SOURCE != 'COMPILED';
+--------------------------------------+-------------------------------------+-----------------+
| VARIABLE_NAME                        | VARIABLE_VALUE                      | VARIABLE_SOURCE |
+--------------------------------------+-------------------------------------+-----------------+
| auto_increment_increment             | 1                                   | EXPLICIT        |
| auto_increment_offset                | 1                                   | EXPLICIT        |
...
| binlog_format                        | ROW                                 | DYNAMIC         |
| binlog_rows_query_log_events         | ON                                  | EXPLICIT        |
| foreign_key_checks                   | ON                                  | DYNAMIC         |
| gtid_executed_compression_period     | 1000                                | EXPLICIT        |
| innodb_buffer_pool_size              | 268435456                           | PERSISTED       |
| innodb_change_buffer_max_size        | 25                                  | EXPLICIT        |
| innodb_log_file_size                 | 100663296                           | PERSISTED       |
| innodb_log_files_in_group            | 2                                   | EXPLICIT        |
| pid_file                             | /data/mysql/mysql3308/data/pxc1.pid | COMMAND_LINE    |
| port                                 | 3308                                | EXPLICIT        |
+--------------------------------------+-------------------------------------+-----------------+
73 rows in set (0.01 sec)

EXPLICIT 來自於參數配置文件 my.cnf
COMMAND_LINE 來自於啓動 mysqld 時額外的 command_line

PERSISTED 來自於數據目錄下 mysqld-auto.cnf

DYNAMIC 來自於 SESSION 變量(包括 GLOBAL 變量的繼承)

3. 查看動態修改的 session 變量(包括 GLOBAL 變量的繼承)

mysql> set session binlog_format='Mixed';
Query OK, 0 rows affected (0.00 sec)

mysql> set global read_only=1;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT t1.VARIABLE_NAME, VARIABLE_VALUE, VARIABLE_SOURCE FROM performance_schema.variables_info t1 JOIN performance_schema.session_variables t2 ON t2.VARIABLE_NAME=t1.VARIABLE_NAME WHERE t1.VARIABLE_SOURCE = 'DYNAMIC';
+--------------------+----------------+-----------------+
| VARIABLE_NAME      | VARIABLE_VALUE | VARIABLE_SOURCE |
+--------------------+----------------+-----------------+
| binlog_format      | MIXED          | DYNAMIC         |
| foreign_key_checks | ON             | DYNAMIC         |
| read_only          | ON             | DYNAMIC         |
+--------------------+----------------+-----------------+
2 rows in set (0.01 sec)

吐槽

MySQL8.0 對於 all 這個權限沒之前直觀了。

mysql> create user fander@'%' identified by 'password';
Query OK, 0 rows affected (0.03 sec)

mysql> grant all on *.* to fander@'%';
Query OK, 0 rows affected (0.02 sec)

mysql> show grants for fander@'%';
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Grants for fander@%                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, RELOAD, SHUTDOWN, PROCESS, FILE, REFERENCES, INDEX, ALTER, SHOW DATABASES, SUPER, CREATE TEMPORARY TABLES, LOCK TABLES, EXECUTE, REPLICATION SLAVE, REPLICATION CLIENT, CREATE VIEW, SHOW VIEW, CREATE ROUTINE, ALTER ROUTINE, CREATE USER, EVENT, TRIGGER, CREATE TABLESPACE, CREATE ROLE, DROP ROLE ON *.* TO `fander`@`%`                                                                                       |
| GRANT APPLICATION_PASSWORD_ADMIN,AUDIT_ADMIN,BACKUP_ADMIN,BINLOG_ADMIN,BINLOG_ENCRYPTION_ADMIN,CLONE_ADMIN,CONNECTION_ADMIN,ENCRYPTION_KEY_ADMIN,GROUP_REPLICATION_ADMIN,INNODB_REDO_LOG_ARCHIVE,PERSIST_RO_VARIABLES_ADMIN,REPLICATION_SLAVE_ADMIN,RESOURCE_GROUP_ADMIN,RESOURCE_GROUP_USER,ROLE_ADMIN,SERVICE_CONNECTION_ADMIN,SESSION_VARIABLES_ADMIN,SET_USER_ID,SYSTEM_USER,SYSTEM_VARIABLES_ADMIN,TABLE_ENCRYPTION_ADMIN,XA_RECOVER_ADMIN ON *.* TO `fander`@`%` |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2 rows in set (0.01 sec)

潛臺詞: 我還得數一數權限是否足夠。

作爲對比,以下是 5.7 的顯示方式：

mysql> create user fander@'%' identified by 'password';
Query OK, 0 rows affected (0.00 sec)

mysql> grant all on *.* to fander@'%';
Query OK, 0 rows affected (0.01 sec)

mysql> show grants for fander@'%';
+---------------------------------------------+
| Grants for fander@%                         |
+---------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'fander'@'%' |
+---------------------------------------------+
1 row in set (0.00 sec)

參考:
https://lefred.be/content/mys...
https://lefred.be/content/wha...

新特性解讀 | MySQL 8.0 輕鬆改配置，雲上友好

背景

修改並持久化動態參數一例

持久化靜態參數一例

清空 persist 持久化參數

相關 performance_schema 表

1. 查看數據庫啓動後載入的 PERSIST 相關參數

2. 查看變量都來自於哪裏

3. 查看動態修改的 session 變量(包括 GLOBAL 變量的繼承)

吐槽

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