sys Schema Tables and Triggers Function Name Description ps_is_instrument_default_timed() Check whether instrument is timed ps_is_thread_instrumented() Check whether thread is instrumented ps_thread_account() Return account for thread ID ps_thread_id() Return thread ID for connection ID ps_thread_stack() Return event information for thread ID ps_thread_trx_info() Return transaction information for thread ID quote_identifier() Return string as quoted identifier sys_get_config() Return  sys  schema configuration option version_major() MySQL server major version number version_minor() MySQL server minor version number version_patch() MySQL server patch release version number The following sections describe  sys  schema tables and triggers. This table contains  sys  schema configuration options, one row per option. Configuration changes made by updating this table persist across client sessions and server restarts. 28.4.2.1 The sys_config Table The  sys_config  table has these columns: • variable • value • set_time • set_by The configuration option name. The configuration option value. The timestamp of the most recent modification to the row. The account that made the most recent modification to the row. The value is  NULL  if the row has not been changed since the  sys  schema was installed. As an efficiency measure to minimize the number of direct reads from the  sys_config  table,  sys  schema functions that use a value from this table check for a user-defined variable with a corresponding name, which is the user-defined variable having the same name plus a  @sys.  prefix. (For example, the variable corresponding to the  diagnostics.include_raw  option is  @sys.diagnostics.include_raw .) If the user-defined variable exists in the current session and is non- NULL , the function uses its value in preference to the value in the  sys_config  table. Otherwise, the function reads and uses the value from the table. In the latter case, the calling function conventionally also sets the corresponding user-defined variable to the table value so that further references to the configuration option within the same session use the variable and need not read the table again. 5138 28.4.2 sys Schema Tables and Triggers