 
Transaction mechanism is used to implement all-or-nothing database update. 
Transaction in DyBASE are started implicitly when update operation is first time performed 
and finished explicitly by <code>commit, rollback</code> or <code>close</code> methods.<P>

Commit of transaction cause synchronous write of changed pages to the disk.
Synchronous write (application is blocked until data is really flushed to the disk) is very expensive operation.
Average positioning time for modern disks is about 10ms, so t