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<p>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:</p>
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<span class="term">Recoverability</span>
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<dd>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.</dd>
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<span class="term">Atomicity</span>
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<dd>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.</dd>
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<span class="term">Isolation</span>
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<dd>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.</dd>
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