MySQL参数log_bin_trust_function_creators介绍

MySQL的有个参数log_bin_trust_function_creators，官方文档对这个参数的介绍、解释如下所示：

log_bin_trust_function_creators

Command-Line Format	--log-bin-trust-function-creators
System Variable	Name	log_bin_trust_function_creators
	Variable Scope	Global
	Dynamic Variable	Yes
Permitted Values	Type	boolean
	Default	FALSE

This variable applies when binary logging is enabled. It controls whether stored function creators can be trusted not to create stored functions that will cause unsafe events to be written to the binary log. If set to 0 (the default), users are not permitted to create or alter stored functions unless they have the SUPER privilege in addition to the CREATE ROUTINE or ALTER ROUTINE privilege. A setting of 0 also enforces the restriction that a function must be declared with the DETERMINISTIC characteristic, or with the READS SQL DATA or NO SQL characteristic. If the variable is set to 1, MySQL does not enforce these restrictions on stored function creation. This variable also applies to trigger creation. See Section 23.7, “Binary Logging of Stored Programs”.

简单介绍一下，当二进制日志启用后，这个变量就会启用。它控制是否可以信任存储函数创建者，不会创建写入二进制日志引起不安全事件的存储函数。如果设置为0（默认值），用户不得创建或修改存储函数，除非它们具有除CREATE ROUTINE或ALTER ROUTINE特权之外的SUPER权限。 设置为0还强制使用DETERMINISTIC特性或READS SQL DATA或NO SQL特性声明函数的限制。 如果变量设置为1，MySQL不会对创建存储函数实施这些限制。 此变量也适用于触发器的创建。 请参见第23.7节“Binary Logging of Stored Programs”。

下面我们测试一下，当开启二进制日志后，如果变量log_bin_trust_function_creators为OFF，那么创建或修改存储函数就会报“ERROR 1418 (HY000): This function has none of DETERMINISTIC, NO SQL, or READS SQL DATA in its declaration and binary logging is enabled (you *might* want to use the less safe log_bin_trust_function_creators variable)”这样的错误，如下所示：

mysql> show variables like 'log_bin';

+---------------+-------+

| Variable_name | Value |

+---------------+-------+

| log_bin       | ON    |

+---------------+-------+

1 row in set (0.00 sec)

mysql>  show variables like '%log_bin_trust_function_creators%';

+---------------------------------+-------+

| Variable_name                   | Value |

+---------------------------------+-------+

| log_bin_trust_function_creators | OFF   |

+---------------------------------+-------+

1 row in set (0.00 sec)

mysql> 

mysql> DELIMITER //

mysql> CREATE FUNCTION GET_UPPER_NAME(emp_id INT)

    -> RETURNS VARCHAR(12)

    -> BEGIN

    ->   RETURN(SELECT UPPER(NAME) FROM TEST WHERE ID=emp_id);

    -> END

    -> //

ERROR 1418 (HY000): This function has none of DETERMINISTIC, NO SQL, or READS SQL DATA in its declaration and binary logging is enabled (you *might* want to use the less safe log_bin_trust_function_creators variable)

mysql> 

在调用存储函数时，也会遇到这个错误,如下测试所示：

mysql> DELIMITER ;

mysql> set global log_bin_trust_function_creators=1;

Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER //

mysql> CREATE FUNCTION GET_UPPER_NAME(emp_id INT)

    -> RETURNS VARCHAR(12)

    -> BEGIN

    ->   RETURN(SELECT UPPER(NAME) FROM TEST WHERE ID=emp_id);

    -> END

    -> //

Query OK, 0 rows affected (0.00 sec)

mysql> SELECT ID,

    ->        GET_UPPER_NAME(ID)

    -> FROM TEST;

    -> //

+------+--------------------+

| ID   | GET_UPPER_NAME(ID) |

+------+--------------------+

|  100 | KERRY              |

|  101 | JIMMY              |

+------+--------------------+

2 rows in set (0.00 sec)

mysql> DELIMITER ;

mysql> set global log_bin_trust_function_creators=0;

Query OK, 0 rows affected (0.00 sec)

mysql> SELECT ID,

    ->        GET_UPPER_NAME(ID)

    -> FROM TEST;

ERROR 1418 (HY000): This function has none of DETERMINISTIC, NO SQL, or READS SQL DATA in its declaration and binary logging is enabled (you *might* want to use the less safe log_bin_trust_function_creators variable)

mysql> 

那么为什么MySQL有这样的限制呢？ 因为二进制日志的一个重要功能是用于主从复制，而存储函数有可能导致主从的数据不一致。所以当开启二进制日志后，参数log_bin_trust_function_creators就会生效，限制存储函数的创建、修改、调用。那么此时如何解决这个问题呢？官方文档介绍如下，具体可以参考23.7 Binary Logging of Stored Programs

If you do not want to require function creators to have the SUPER privilege (for example, if all users with the CREATE ROUTINE privilege on your system are experienced application developers), set the global log_bin_trust_function_creators system variable to 1. You can also set this variable by using the --log-bin-trust-function-creators=1 option when starting the server. If binary logging is not enabled, log_bin_trust_function_creators does not apply. SUPER is not required for function creation unless, as described previously, the DEFINER value in the function definition requires it.

If a function that performs updates is nondeterministic, it is not repeatable. This can have two undesirable effects:

·         It will make a slave different from the master.

·         Restored data will be different from the original data.

To deal with these problems, MySQL enforces the following requirement: On a master server, creation and alteration of a function is refused unless you declare the function to be deterministic or to not modify data. Two sets of function characteristics apply here:

·         The DETERMINISTIC and NOT DETERMINISTIC characteristics indicate whether a function always produces the same result for given inputs. The default is NOT DETERMINISTIC if neither characteristic is given. To declare that a function is deterministic, you must specify DETERMINISTIC explicitly.

·         The CONTAINS SQL, NO SQL, READS SQL DATA, and MODIFIES SQL DATA characteristics provide information about whether the function reads or writes data. Either NO SQL or READS SQL DATA indicates that a function does not change data, but you must specify one of these explicitly because the default is CONTAINS SQL if no characteristic is given.

·

1： 如果数据库没有使用主从复制，那么就可以将参数log_bin_trust_function_creators设置为1。

mysql> set global log_bin_trust_function_creators=1;

这个动态设置的方式会在服务重启后失效，所以我们还必须在my.cnf中设置，加上log_bin_trust_function_creators=1，这样就会永久生效。

2：明确指明函数的类型，如果我们开启了二进制日志， 那么我们就必须为我们的function指定一个参数。其中下面几种参数类型里面，只有 DETERMINISTIC, NO SQL 和 READS SQL DATA 被支持。这样一来相当于明确的告知MySQL服务器这个函数不会修改数据。

1 DETERMINISTIC 确定的

2 NO SQL 没有SQl语句，当然也不会修改数据

3 READS SQL DATA 只是读取数据，当然也不会修改数据

4 MODIFIES SQL DATA 要修改数据

5 CONTAINS SQL 包含了SQL语句

mysql> show variables like 'log_bin_trust_function_creators';

+---------------------------------+-------+

| Variable_name                   | Value |

+---------------------------------+-------+

| log_bin_trust_function_creators | OFF   |

+---------------------------------+-------+

1 row in set (0.00 sec)

mysql> DROP FUNCTION GET_UPPER_NAME;

Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER //

mysql> CREATE FUNCTION GET_UPPER_NAME(emp_id INT)

    -> RETURNS VARCHAR(12)

    -> READS SQL DATA

    -> BEGIN

    ->   RETURN(SELECT UPPER(NAME) FROM TEST WHERE ID=emp_id);

    -> END

    -> //

Query OK, 0 rows affected (0.01 sec)

mysql> DELIMITER ;

mysql> SELECT ID,

    ->        GET_UPPER_NAME(ID)

    -> FROM TEST;

+------+--------------------+

| ID   | GET_UPPER_NAME(ID) |

+------+--------------------+

|  100 | KERRY              |

|  101 | JIMMY              |

+------+--------------------+

2 rows in set (0.00 sec)