sys Schema Tables and Triggers For example, the  statement_truncate_len  option controls the maximum length of statements returned by the  format_statement()  function. The default is 64. To temporarily change the value to 32 for your current session, set the corresponding  @sys.statement_truncate_len  user-defined variable: mysql>  SET @stmt = ’SELECT variable, value, set_time, set_by FROM sys_config’; mysql>  SELECT sys.format_statement(@stmt); +----------------------------------------------------------+ | sys.format_statement(@stmt) | +----------------------------------------------------------+ | SELECT variable, value, set_time, set_by FROM sys_config | +----------------------------------------------------------+ mysql>  SET @sys.statement_truncate_len = 32; mysql>  SELECT sys.format_statement(@stmt); +-----------------------------------+ | sys.format_statement(@stmt) | +-----------------------------------+ | SELECT variabl ... ROM sys_config | +-----------------------------------+ mysql>  SET @sys.statement_truncate_len = NULL; mysql>  SELECT sys.format_statement(@stmt); +----------------------------------------------------------+ | sys.format_statement(@stmt) | +----------------------------------------------------------+ | SELECT variable, value, set_time, set_by FROM sys_config | +----------------------------------------------------------+ Subsequent invocations of  format_statement()  within the session continue to use the user-defined variable value (32), rather than the value stored in the table (64). To stop using the user-defined variable and revert to using the value in the table, set the variable to  NULL within your session: Alternatively, end your current session (causing the user-defined variable to no longer exist) and begin a new session. The conventional relationship just described between options in the  sys_config  table and user-defined variables can be exploited to make temporary configuration changes that end when your session ends. However, if you set a user-defined variable and then subsequently change the corresponding table value within the same session, the changed table value is not used in that session as long as the user-defined variable exists with a non- NULL  value. (The changed table value  is  used in other sessions in which the user-defined variable is not assigned.) The following list describes the options in the  sys_config  table and the corresponding user-defined variables: • diagnostics.allow_i_s_tables ,  @sys.diagnostics.allow_i_s_tables • diagnostics.include_raw ,  @sys.diagnostics.include_raw • ps_thread_trx_info.max_length ,  @sys.ps_thread_trx_info.max_length If this option is  ON , the  diagnostics()  procedure is permitted to perform table scans on the INFORMATION_SCHEMA.TABLES  table. This can be expensive if there are many tables. The default is OFF . If this option is  ON , the  diagnostics()  procedure includes the raw output from querying the  metrics view. The default is  OFF . The maximum length for JSON output produced by the  ps_thread_trx_info()  function. The default is 65535. 5139