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90 lines
4.2 KiB
HTML
90 lines
4.2 KiB
HTML
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<?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>Berkeley DB XA Implementation</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="Berkeley DB Programmer's Reference Guide" />
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<link rel="up" href="xa.html" title="Chapter 13. Distributed Transactions" />
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<link rel="prev" href="xa.html" title="Chapter 13. Distributed Transactions" />
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<link rel="next" href="xa_build.html" title="Building a Global Transaction Manager" />
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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 11.2.5.2</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">Berkeley DB XA Implementation</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="xa.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 13.
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Distributed Transactions
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="xa_build.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="id3911864"></a>Berkeley DB XA Implementation</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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Berkeley DB provides support for distributed transactions using the two-phase commit protocol
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via its <a href="../api_reference/C/txnprepare.html" class="olink">DB_TXN->prepare()</a> interfaces.
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The <a href="../api_reference/C/txnprepare.html" class="olink">DB_TXN->prepare()</a> method performs the first phase of a
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two-phase commit, flushing the log to disk, and associating a global
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transaction ID with the underlying Berkeley DB transaction.
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This global transaction ID is used by the global transaction manager to
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identify the Berkeley DB transaction, and will be returned by the
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<a href="../api_reference/C/txnrecover.html" class="olink">DB_ENV->txn_recover()</a> method when it is called during recovery.
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</p>
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<p>
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However, Berkeley DB does not perform distributed deadlock detection.
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Instead, when being used as an XA resource manager, Berkeley DB acquires all locks
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in a non-blocking mode. This results in pre-emptive abort of transactions that have the potential to deadlock.
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While this can lead to more transactions being aborted than is strictly necessary,
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it avoids system-wide hanging due to distributed deadlocks.
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</p>
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<p>When using distributed transactions, there is no way to perform
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hot backups of multiple environments and guarantee that the backups
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are globally transaction-consistent across these multiple environments.
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If backups are desired, then all write transactions should be suspended;
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that is, active write transactions must be allowed to complete and no
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new write transactions should be begun. Once there are no active write
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transactions, the logs may be copied for backup purposes and the backup
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will be consistent across the multiple environments.</p>
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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="xa.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="xa.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="xa_build.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">Chapter 13.
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Distributed Transactions
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</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"> Building a Global Transaction Manager</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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