why.so

berkeley db 4.6.21的源码。berkeley db是一个简单的数据库管理系统

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([dnl
Perhaps the first question to answer is "Why transactions?"  There are
a number of reasons to include transactional support in your applications.
The most common ones are the following:])

m4_tagbegin

m4_tag([Recoverability], [dnl
Applications often need to ensure that no matter how the system or
application fails, previously saved data is available the next time the
application runs.  This is often called Durability.])

m4_tag([Atomicity], [dnl
Applications may need to make multiple changes to one or more databases,
but ensure that either all of the changes happen, or none of them
happens.  Transactions guarantee that a group of changes are atomic;
that is, if the application or system fails, either all of the changes
to the databases will appear when the application next runs, or none of
them.])

m4_tag([Isolation], [dnl
Applications may need to make changes in isolation, that is, ensure that
only 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 all
other transactions either completed before or after its transaction.])

m4_tagend

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