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142 lines
6.0 KiB
142 lines
6.0 KiB
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Nested Transactions</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" />
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<link rel="up" href="usingtxns.html" title="Chapter 3. Transaction Basics" />
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<link rel="prev" href="autocommit.html" title="Auto Commit" />
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<link rel="next" href="txncursor.html" title="Transactional Cursors" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 12.1.6.2</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Nested Transactions</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="autocommit.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 3. Transaction Basics</th>
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<td width="20%" align="right"> <a accesskey="n" href="txncursor.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="nestedtxn"></a>Nested Transactions</h2>
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</div>
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</div>
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</div>
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<p>
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A <span class="emphasis"><em>nested transaction</em></span> is used to provide a
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transactional guarantee for a subset of operations performed within
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the scope of a larger transaction. Doing this allows you to commit
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and abort the subset of operations independently of the larger
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transaction.
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</p>
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<p>
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The rules to the usage of a nested transaction are as follows:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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While the nested (child) transaction is active, the parent
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transaction may not perform any operations other than to commit
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or abort, or to create more child transactions.
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</p>
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</li>
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<li>
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<p>
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Committing a nested transaction has no effect on the state
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of the parent transaction. The parent transaction is still
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uncommitted. However, the parent transaction can now
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see any modifications made by the child transaction.
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Those modifications, of course, are still hidden to all
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other transactions until the parent also commits.
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</p>
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</li>
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<li>
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<p>
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Likewise, aborting the nested transaction has no effect on
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the state of the parent transaction. The only result of the
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abort is that neither the parent nor any
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other transactions will see any of the
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database modifications performed under the protection of the
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nested transaction.
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</p>
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</li>
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<li>
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<p>
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If the parent transaction commits or aborts while it has
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active children, the child transactions are resolved in the
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same way as the parent. That is, if the parent aborts, then
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the child transactions abort as well. If the parent commits,
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then whatever modifications have been performed by the child
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transactions are also committed.
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</p>
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</li>
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<li>
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<p>
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The locks held by a nested transaction are not released when
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that transaction commits. Rather, they are now held by the
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parent transaction until such a time as that parent commits.
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</p>
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</li>
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<li>
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<p>
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Any database modifications performed by the nested transaction
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are not visible outside of the larger encompassing
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transaction until such a time as that parent transaction is
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committed.
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</p>
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</li>
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<li>
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<p>
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The depth of the nesting that you can achieve with nested
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transaction is limited only by memory.
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</p>
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</li>
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</ul>
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</div>
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<p>
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To create a nested transaction, simply pass the parent transaction's
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handle when you created the nested transaction's handle. For
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example:
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</p>
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<pre class="programlisting"> // parent transaction
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DbTxn *parentTxn, *childTxn;
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ret = myEnv.txn_begin(NULL, &parentTxn, 0);
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// child transaction
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ret = myEnv.txn_begin(parent_txn, &childTxn, 0); </pre>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="autocommit.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="usingtxns.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="txncursor.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Auto Commit </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Transactional Cursors</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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