m4_comment([$Id: why.so,v 1.7 2003/11/04 14:53:27 bostic Exp $])m4_ref_title(m4_tam Applications,    Why transactions?,, transapp/intro, transapp/term)m4_p([dnlPerhaps the first question to answer is "Why transactions?"  There area number of reasons to include transactional support in your applications.The most common ones are the following:])m4_tagbeginm4_tag([Recoverability], [dnlApplications often need to ensure that no matter how the system orapplication fails, previously saved data is available the next time theapplication runs.  This is often called Durability.])m4_tag([Atomicity], [dnlApplications may need to make multiple changes to one or more databases,but ensure that either all of the changes happen, or none of themhappens.  Transactions guarantee that a group of changes are atomic;that is, if the application or system fails, either all of the changesto the databases will appear when the application next runs, or none ofthem.])m4_tag([Isolation], [dnlApplications may need to make changes in isolation, that is, ensure thatonly a single thread of control is modifying a key/data pair at a time.Transactions ensure each thread of control sees all records as if allother transactions either completed before or after its transaction.])m4_tagendm4_page_footer