max_execution_time

Description

max_execution_time specifies the execution timeout for read-only SELECT statements in milliseconds.

Considerations

The max_execution_time variable takes effect only in the following scenarios:

• The cluster version meets the requirements: the minimum cluster version is V4.4.2 BP1 or later.
• The value of the MAX_EXECUTION_TIME parameter is greater than 0 (indicating that the feature is enabled).
• The current SQL statement is a single, read-only SELECT statement.

The max_execution_time variable does not take effect in the following scenarios, and is instead controlled by the ob_query_timeout variable:

• The cluster version is earlier than V4.4.2 BP1.
• The value of the MAX_EXECUTION_TIME parameter is 0.
• The SQL statement is not a SELECT statement.
• The SQL statement is a multi-statement and the timestamp of ob_query_timeout is earlier than that of max_execution_time.
• The SQL statement is a SELECT statement but is not read-only. For example, if a SELECT statement contains a user-defined function (UDF) that defines a data manipulation language (DML) operation, the timeout for the SELECT statement is controlled by ob_query_timeout.

Privilege requirements

• Query variables

  • Global level

    The sys tenant and all user tenants can use the SHOW VARIABLES statement or the SYS.TENANT_VIRTUAL_GLOBAL_VARIABLE view (Oracle mode) or the information_schema.GLOBAL_VARIABLES view (MySQL mode) to view the value of a global system variable.

  • Session level

    The sys tenant and all user tenants can use the SHOW VARIABLES statement or the SYS.TENANT_VIRTUAL_SESSION_VARIABLE view (Oracle mode) or the information_schema.SESSION_VARIABLES view (MySQL mode) to view the value of a session system variable.

• Modify variables

  • The sys tenant can directly modify the value of a global system variable.

  • A MySQL user tenant must have the SUPER or ALTER SYSTEM privilege to modify the value of a global system variable.

  • An Oracle user tenant must have the ALTER SYSTEM privilege to modify the value of a global system variable.

Attributes

Examples

Set the execution timeout of a SELECT statement to 2 milliseconds.

obclient> SET GLOBAL max_execution_time=2;

References