How to know that all have finished?

1. periodically, write log record <CHKPT (T1,..,Tk)>
   (contains references to all active transactions ⇒ active tx table)
2. continue normal processing (e.g. new tx's can start)
3. when all of T1,..,Tk have completed,
   write log record <ENDCHKPT> and flush log

Note: tx manager maintains chkpt and active tx information