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<h1>Concurrency Control And Locking</h1>
<p>Concurrency control and locking is a mechanism used
by DBMS to ensure that database transactions are executed in a safe manner. Atomicity, consistency, and isolation are
achieved through concurrency control and locking. See <a href="acid_model.html" class="wikiLink">ACID Model</a>.</p>
<p>When data
is accessed from more than one transaction concurrently, it is usually
necessary to ensure that only one transaction at a time can change a data item.
Locking is a way to do this. Because of locking, all changes to a particular
data item will be made in the correct order in a transaction. See
<a href="acid_model/isolation.html" class="wikiLink">Isolation</a>.</p>
<p>The
following types of locking are usually distinguished:</p><p><div class="childTopicList">More Reading:<ul>
<li><p><a href="concurrency_control_and_locking/pessimistic_locking.html" class="wikiLink">Pessimistic Locking</a></p></li>
<li><p><a href="concurrency_control_and_locking/optimistic_locking.html" class="wikiLink">Optimistic Locking</a></p></li>
<li><p><a href="concurrency_control_and_locking/overly_optimistic_locking.html" class="wikiLink">Overly Optimistic Locking</a></p></li>
<li><p><a href="concurrency_control_and_locking/concurrency_control_in_db4o.html" class="wikiLink">Concurrency Control In Db4o</a></p></li>
<li><p><a href="concurrency_control_and_locking/types_of_locks.html" class="wikiLink">Types Of Locks</a></p></li>
<li><p><a href="concurrency_control_and_locking/locks_in_db4o.html" class="wikiLink">Locks In Db4o</a></p></li>
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This revision (2) was last Modified 2007-05-22T11:44:41 by Tetyana.
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