System Triggers

System Triggers

Generic System Trigger _on_system_event

The generic system trigger allows the owner of the SQL server to program a reaction for events concerning server operation. This events affect the server as a whole (e.g. database back-up), unlike the specific events in database applications.

The generic system trigger is a function:

FUNCTION _ON_SYSTEM_EVENT(IN event_num INT, IN ipar INT, IN spar CHAR(255)) RETURNS INT;
BEGIN
  ...
END

This function is called by the SQL server on certain events occurrences. The event_num parameter specifies the concerned event. The meaning of the rest of the parameters and the returned value depends on a specific event.

This trigger is run with Config_admin group (configuration administrator) privileges.

You can affect further SQL server operation by returning a certain value for some events.

The "Database file backup" Event (Event #1)

This event occurs just before the server takes steps to create the backup copy of a database file. The event_num parameter has a value equal to 1. The ipar parameter equals 0 on automatic periodic backup or equals 1 on a backup called by client API (by button Backup now as well). The spar parameter value is not defined.

It the function returns -1, then the backup was recalled. The backup was made successfully for other return values.

Example:

User function Can_start_backup_test(), decides (someway...) if a backup can begin:

FUNCTION _on_system_event(IN event_num INT, IN ipar INT, IN spar CHAR(255)) RETURNS INT;
BEGIN
  CASE
    WHEN event_num = 1 THEN // is it backup
     IF Can_start_backup_test() THEN
       CALL Log_write('backup started: par='+Int2str(ipar));
       RETURN 1;
     ELSE
       RETURN -1;
     END IF;
  ELSE
    RETURN 1; // default for other events
  END CASE;
END

System Triggers

System Triggers