mirror of
https://github.com/yasuhirokimura/db18
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Yasuhiro KIMURA
98 lines
4.7 KiB
HTML
98 lines
4.7 KiB
HTML
<?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>Configuring 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="Berkeley DB Programmer's Reference Guide" />
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<link rel="up" href="txn.html" title="Chapter 20. The Transaction Subsystem" />
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<link rel="prev" href="txn.html" title="Chapter 20. The Transaction Subsystem" />
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<link rel="next" href="txn_limits.html" title="Transaction limits" />
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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 18.1.40</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">Configuring 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="txn.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 20. The Transaction Subsystem </th>
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<td width="20%" align="right"> <a accesskey="n" href="txn_limits.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="txn_config"></a>Configuring 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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The application may change the number of simultaneous
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outstanding transactions supported by the Berkeley DB
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environment by calling the <a href="../api_reference/C/envset_tx_max.html" class="olink">DB_ENV->set_tx_max()</a> method. This will
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also set the size of the underlying transaction subsystem's
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region. When the number of outstanding transactions is
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reached, additional calls to <a href="../api_reference/C/txnbegin.html" class="olink">DB_ENV->txn_begin()</a> will fail until some
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active transactions complete.
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</p>
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<p>
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The application can limit how long a transaction runs or
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blocks on contested resources. The <a href="../api_reference/C/envset_timeout.html" class="olink">DB_ENV->set_timeout()</a> method
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specifies the length of the timeout. This value is checked
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whenever deadlock detection is performed or when the
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transaction is about to block on a lock that cannot be
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immediately granted. Because timeouts are only checked at
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these times, the accuracy of the timeout depends on how often
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deadlock detection is performed or how frequently the
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transaction blocks.
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</p>
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<p>
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There is an additional parameter used in configuring
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transactions; the <a href="../api_reference/C/envset_flags.html#envset_flags_DB_TXN_NOSYNC" class="olink">DB_TXN_NOSYNC</a>. Setting the <a href="../api_reference/C/envset_flags.html#envset_flags_DB_TXN_NOSYNC" class="olink">DB_TXN_NOSYNC</a>
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flag to <a href="../api_reference/C/envset_flags.html" class="olink">DB_ENV->set_flags()</a> when opening a transaction region
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changes the behavior of transactions to not write or
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synchronously flush the log during transaction commit.
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</p>
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<p>
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This change may significantly increase application
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transactional throughput. However, it means that although
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transactions will continue to exhibit the ACI (atomicity,
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consistency, and isolation) properties, they will not have D
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(durability). Database integrity will be maintained, but it is
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possible that some number of the most recently committed
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transactions may be undone during recovery instead of being
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redone.
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</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="txn.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="txn.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="txn_limits.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 20. The Transaction Subsystem </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"> Transaction limits</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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