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<th colspan="3" align="center">Multi-threaded
<span>and Multi-process</span>
Applications</th>
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<h2 class="title" style="clear: both"><a id="multithread-intro"></a>Multi-threaded
<span>and Multi-process</span>
Applications</h2>
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<p>
DB is designed to support multi-threaded <span>and
multi-process</span> applications, but their usage means
you must pay careful attention to issues of concurrency.
Transactions help your application's concurrency by providing various levels of
isolation for your threads of control. In addition, DB
provides mechanisms that allow you to detect and respond to
deadlocks.
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<p>
<span class="emphasis"><em>Isolation</em></span> means that database modifications made by
one transaction will not normally be seen by readers from another
transaction until the first commits its changes. Different threads
use different transaction handles, so
this mechanism is normally used to provide isolation between
database operations performed by different threads.
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Note that DB supports different isolation levels. For example,
you can configure your application to see uncommitted reads, which means
that one transaction can see data that has been modified but not yet
committed by another transaction. Doing this might mean your
transaction reads data "dirtied" by another transaction,
but which subsequently might change before that
other transaction commits its changes.
On the other hand, lowering your isolation
requirements means that your application can experience
improved throughput due to reduced lock contention.
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For more information on concurrency, on managing isolation
levels, and on deadlock detection, see <a class="xref" href="txnconcurrency.html" title="Chapter 4. Concurrency">Concurrency</a>.
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