2011-09-13 17:44:24 +00:00
|
|
|
|
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
|
|
|
|
|
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
|
|
|
|
|
<html xmlns="http://www.w3.org/1999/xhtml">
|
|
|
|
|
|
<head>
|
|
|
|
|
|
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
|
|
|
|
|
|
<title>Non-Durable Transactions</title>
|
|
|
|
|
|
<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
|
|
|
|
|
|
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
|
|
|
|
|
|
<link rel="start" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" />
|
|
|
|
|
|
<link rel="up" href="usingtxns.html" title="Chapter 3. Transaction Basics" />
|
|
|
|
|
|
<link rel="prev" href="usingtxns.html" title="Chapter 3. Transaction Basics" />
|
|
|
|
|
|
<link rel="next" href="abortresults.html" title="Aborting a Transaction" />
|
|
|
|
|
|
</head>
|
|
|
|
|
|
<body>
|
|
|
|
|
|
<div xmlns="" class="navheader">
|
|
|
|
|
|
<div class="libver">
|
2012-11-14 21:35:20 +00:00
|
|
|
|
<p>Library Version 11.2.5.3</p>
|
2011-09-13 17:44:24 +00:00
|
|
|
|
</div>
|
|
|
|
|
|
<table width="100%" summary="Navigation header">
|
|
|
|
|
|
<tr>
|
|
|
|
|
|
<th colspan="3" align="center">Non-Durable Transactions</th>
|
|
|
|
|
|
</tr>
|
|
|
|
|
|
<tr>
|
|
|
|
|
|
<td width="20%" align="left"><a accesskey="p" href="usingtxns.html">Prev</a> </td>
|
|
|
|
|
|
<th width="60%" align="center">Chapter 3. Transaction Basics</th>
|
|
|
|
|
|
<td width="20%" align="right"> <a accesskey="n" href="abortresults.html">Next</a></td>
|
|
|
|
|
|
</tr>
|
|
|
|
|
|
</table>
|
|
|
|
|
|
<hr />
|
|
|
|
|
|
</div>
|
|
|
|
|
|
<div class="sect1" lang="en" xml:lang="en">
|
|
|
|
|
|
<div class="titlepage">
|
|
|
|
|
|
<div>
|
|
|
|
|
|
<div>
|
|
|
|
|
|
<h2 class="title" style="clear: both"><a id="nodurabletxn"></a>Non-Durable Transactions</h2>
|
|
|
|
|
|
</div>
|
|
|
|
|
|
</div>
|
|
|
|
|
|
</div>
|
|
|
|
|
|
<p>
|
|
|
|
|
|
As previously noted, by default transaction commits are
|
|
|
|
|
|
durable because they cause the modifications performed
|
|
|
|
|
|
under the transaction to be synchronously recorded in
|
|
|
|
|
|
your on-disk log files. However, it is possible to use
|
|
|
|
|
|
non-durable transactions.
|
|
|
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
|
|
|
You may want non-durable transactions for performance
|
|
|
|
|
|
reasons. For example, you might be using transactions
|
|
|
|
|
|
simply for the isolation guarantee.
|
|
|
|
|
|
|
|
|
|
|
|
<span>
|
|
|
|
|
|
In this case, you might
|
|
|
|
|
|
not want a durability guarantee and so you may want to
|
|
|
|
|
|
prevent the disk I/O that normally accompanies a
|
|
|
|
|
|
transaction commit.
|
|
|
|
|
|
</span>
|
|
|
|
|
|
|
|
|
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
|
|
|
There are several ways to remove the durability guarantee
|
|
|
|
|
|
for your transactions:
|
|
|
|
|
|
</p>
|
|
|
|
|
|
<div class="itemizedlist">
|
|
|
|
|
|
<ul type="disc">
|
|
|
|
|
|
<li>
|
|
|
|
|
|
<p>
|
|
|
|
|
|
Specify
|
|
|
|
|
|
<span>
|
|
|
|
|
|
<code class="literal">DB_TXN_NOSYNC</code> using the
|
|
|
|
|
|
|
|
|
|
|
|
<code class="methodname">DbEnv::set_flags()</code>
|
|
|
|
|
|
method.
|
|
|
|
|
|
</span>
|
|
|
|
|
|
|
|
|
|
|
|
This causes DB to not synchronously force any log
|
|
|
|
|
|
data to disk upon transaction commit. That is, the modifications are held entirely
|
|
|
|
|
|
in the in-memory cache and the logging information is not forced to the filesystem for
|
|
|
|
|
|
long-term storage.
|
|
|
|
|
|
Note, however, that the logging
|
|
|
|
|
|
data will eventually make it to the filesystem (assuming no
|
|
|
|
|
|
application or OS crashes) as a part of DB's
|
|
|
|
|
|
management of its logging buffers and/or cache.
|
|
|
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
|
|
|
This form of a commit provides a weak durability
|
|
|
|
|
|
guarantee because data loss can occur due to
|
|
|
|
|
|
an application
|
|
|
|
|
|
or OS crash.
|
|
|
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
|
|
|
This behavior is specified on a per-environment
|
|
|
|
|
|
handle basis. In order for your application to exhibit consistent
|
|
|
|
|
|
behavior, you need to specify this
|
|
|
|
|
|
<span>flag</span>
|
|
|
|
|
|
|
|
|
|
|
|
for all of the environment handles used in your application.
|
|
|
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
|
|
|
You can achieve this behavior on a transaction by transaction basis by
|
|
|
|
|
|
<span>
|
|
|
|
|
|
specifying <code class="literal">DB_TXN_NOSYNC</code> to the
|
|
|
|
|
|
|
|
|
|
|
|
<code class="methodname">DbTxn::commit()</code>
|
|
|
|
|
|
|
|
|
|
|
|
method.
|
|
|
|
|
|
</span>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
</p>
|
|
|
|
|
|
</li>
|
|
|
|
|
|
<li>
|
|
|
|
|
|
<p>
|
|
|
|
|
|
Specify
|
|
|
|
|
|
<span>
|
|
|
|
|
|
<code class="literal">DB_TXN_WRITE_NOSYNC</code> using the
|
|
|
|
|
|
|
|
|
|
|
|
<code class="methodname">DbEnv::set_flags()</code>
|
|
|
|
|
|
method.
|
|
|
|
|
|
</span>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
This causes
|
|
|
|
|
|
<span>
|
|
|
|
|
|
logging
|
|
|
|
|
|
</span>
|
|
|
|
|
|
data to be synchronously
|
|
|
|
|
|
written to the OS's file system buffers upon
|
|
|
|
|
|
transaction commit. The data will eventually be
|
|
|
|
|
|
written to disk, but this occurs when the
|
|
|
|
|
|
operating system chooses to schedule the
|
|
|
|
|
|
activity; the transaction commit can complete
|
|
|
|
|
|
successfully before this disk I/O is performed
|
|
|
|
|
|
by the OS.
|
|
|
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
|
|
|
This form of commit protects you against application
|
|
|
|
|
|
crashes, but not against OS
|
|
|
|
|
|
crashes. This method offers less room for the possibility of data loss than does
|
|
|
|
|
|
<span><code class="literal">DB_TXN_NOSYNC</code>.</span>
|
|
|
|
|
|
|
|
|
|
|
|
</p>
|
|
|
|
|
|
<p>
|
|
|
|
|
|
This behavior is specified on a per-environment
|
|
|
|
|
|
handle basis. In order for your application to exhibit consistent
|
|
|
|
|
|
behavior, you need to specify this
|
|
|
|
|
|
<span>flag</span>
|
|
|
|
|
|
|
|
|
|
|
|
for all of the environment handles used in your application.
|
|
|
|
|
|
</p>
|
|
|
|
|
|
</li>
|
|
|
|
|
|
<li>
|
|
|
|
|
|
<p>
|
|
|
|
|
|
Maintain your logs entirely in-memory. In this
|
|
|
|
|
|
case, your logs are never written to disk. The
|
|
|
|
|
|
result is that you lose all durability guarantees.
|
|
|
|
|
|
See
|
|
|
|
|
|
<a class="xref" href="logconfig.html#inmemorylogging" title="Configuring In-Memory Logging">Configuring In-Memory Logging</a>
|
|
|
|
|
|
for more information.
|
|
|
|
|
|
</p>
|
|
|
|
|
|
</li>
|
|
|
|
|
|
</ul>
|
|
|
|
|
|
</div>
|
|
|
|
|
|
</div>
|
|
|
|
|
|
<div class="navfooter">
|
|
|
|
|
|
<hr />
|
|
|
|
|
|
<table width="100%" summary="Navigation footer">
|
|
|
|
|
|
<tr>
|
|
|
|
|
|
<td width="40%" align="left"><a accesskey="p" href="usingtxns.html">Prev</a> </td>
|
|
|
|
|
|
<td width="20%" align="center">
|
|
|
|
|
|
<a accesskey="u" href="usingtxns.html">Up</a>
|
|
|
|
|
|
</td>
|
|
|
|
|
|
<td width="40%" align="right"> <a accesskey="n" href="abortresults.html">Next</a></td>
|
|
|
|
|
|
</tr>
|
|
|
|
|
|
<tr>
|
|
|
|
|
|
<td width="40%" align="left" valign="top">Chapter 3. Transaction Basics </td>
|
|
|
|
|
|
<td width="20%" align="center">
|
|
|
|
|
|
<a accesskey="h" href="index.html">Home</a>
|
|
|
|
|
|
</td>
|
|
|
|
|
|
<td width="40%" align="right" valign="top"> Aborting a Transaction</td>
|
|
|
|
|
|
</tr>
|
|
|
|
|
|
</table>
|
|
|
|
|
|
</div>
|
|
|
|
|
|
</body>
|
|
|
|
|
|
</html>
|
