You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
212 lines
9.0 KiB
212 lines
9.0 KiB
<?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>Configuring the Transaction Subsystem</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="txnindices.html" title="Secondary Indices with Transaction Applications" />
|
|
<link rel="next" href="txnconcurrency.html" title="Chapter 4. Concurrency" />
|
|
</head>
|
|
<body>
|
|
<div xmlns="" class="navheader">
|
|
<div class="libver">
|
|
<p>Library Version 12.1.6.2</p>
|
|
</div>
|
|
<table width="100%" summary="Navigation header">
|
|
<tr>
|
|
<th colspan="3" align="center">Configuring the Transaction Subsystem</th>
|
|
</tr>
|
|
<tr>
|
|
<td width="20%" align="left"><a accesskey="p" href="txnindices.html">Prev</a> </td>
|
|
<th width="60%" align="center">Chapter 3. Transaction Basics</th>
|
|
<td width="20%" align="right"> <a accesskey="n" href="txnconcurrency.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="maxtxns"></a>Configuring the Transaction Subsystem</h2>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<p>
|
|
Most of the configuration activities that you need to perform
|
|
for your transactional DB application will involve the
|
|
locking and logging subsystems. See
|
|
<a class="xref" href="txnconcurrency.html" title="Chapter 4. Concurrency">Concurrency</a>
|
|
and
|
|
<a class="xref" href="filemanagement.html" title="Chapter 5. Managing DB Files">Managing DB Files</a>
|
|
for details.
|
|
</p>
|
|
<p>
|
|
However, there are a couple of things that you can do to
|
|
configure your transaction subsystem directly. These things
|
|
are:
|
|
</p>
|
|
<div class="itemizedlist">
|
|
<ul type="disc">
|
|
<li>
|
|
<span>
|
|
<p>
|
|
|
|
<span>
|
|
Configure
|
|
</span>
|
|
|
|
the maximum number of simultaneous
|
|
transactions needed by your application.
|
|
In general, you should not need to do this unless you
|
|
use deeply nested transactions or you have many threads all
|
|
of which have active transactions. In addition, you may
|
|
need to configure a higher maximum number of transactions if you
|
|
are using snapshot isolation. See
|
|
<a class="xref" href="isolation.html#sisolation_maxtxn" title="Snapshot Isolation Transactional Requirements">Snapshot Isolation Transactional Requirements</a>
|
|
for details.
|
|
</p>
|
|
<p>
|
|
By default, your application can support 20 active
|
|
transactions.
|
|
</p>
|
|
<p>
|
|
You can set the maximum number of simultaneous
|
|
transactions supported by your application using
|
|
<span>
|
|
the
|
|
|
|
<code class="methodname">DbEnv::set_tx_max()</code>
|
|
method. Note that this method must be called
|
|
before the environment has been opened.
|
|
</span>
|
|
|
|
</p>
|
|
<p>
|
|
If your application has exceeded this maximum value,
|
|
then any attempt to begin a new transaction will fail.
|
|
</p>
|
|
<p>
|
|
This value can also be set using the
|
|
<code class="literal">DB_CONFIG</code> file's
|
|
<code class="literal">set_tx_max</code> parameter. Remember that
|
|
the <code class="literal">DB_CONFIG</code> must reside in your
|
|
environment home directory.
|
|
</p>
|
|
</span>
|
|
</li>
|
|
<li>
|
|
<span>
|
|
<p>
|
|
<span>
|
|
Configure the timeout value for your transactions.
|
|
</span>
|
|
|
|
|
|
This value represents the longest period of time a
|
|
transaction can be active. Note, however, that
|
|
transaction timeouts are checked only when DB
|
|
examines its lock tables for blocked locks
|
|
(see <a class="xref" href="blocking_deadlocks.html" title="Locks, Blocks, and Deadlocks">Locks, Blocks, and Deadlocks</a>
|
|
for more information). Therefore, a transaction's timeout can
|
|
have expired, but the application will not be notified until DB
|
|
has a reason to examine its lock tables.
|
|
</p>
|
|
<p>
|
|
Be aware that some transactions may be
|
|
inappropriately timed out before the transaction has a
|
|
chance to complete. You should therefore use this
|
|
mechanism only if you know your application
|
|
might have unacceptably long transactions and
|
|
you want to make sure your application will
|
|
not stall during their execution.
|
|
(This might happen if, for example, your
|
|
transaction blocks or requests too much
|
|
data.)
|
|
</p>
|
|
<p>
|
|
Note that by default transaction timeouts are set to 0 seconds, which means that they never time
|
|
out.
|
|
</p>
|
|
<p>
|
|
To set the maximum timeout value for your transactions,
|
|
use the
|
|
|
|
<span><code class="methodname">DbEnv::set_timeout()</code></span>
|
|
|
|
method. This method configures the entire
|
|
environment; not just the handle used to set the
|
|
configuration. Further, this value may
|
|
be set at any time during the application's
|
|
lifetime.
|
|
</p>
|
|
<p>
|
|
This value can also be set using the
|
|
<code class="literal">DB_CONFIG</code> file's
|
|
<code class="literal">set_txn_timeout</code> parameter.
|
|
</p>
|
|
|
|
</span>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<p>
|
|
For example:
|
|
</p>
|
|
<pre class="programlisting">#include "db_cxx.h"
|
|
|
|
...
|
|
|
|
int main(void)
|
|
{
|
|
u_int32_t env_flags = DB_CREATE | // If the environment does not
|
|
// exist, create it.
|
|
DB_INIT_LOCK | // Initialize locking
|
|
DB_INIT_LOG | // Initialize logging
|
|
DB_INIT_MPOOL | // Initialize the cache
|
|
DB_THREAD | // Free-thread the env handle
|
|
DB_INIT_TXN; // Initialize transactions
|
|
|
|
std::string envHome("/export1/testEnv");
|
|
DbEnv myEnv(0);
|
|
|
|
try {
|
|
|
|
// Configure a maximum transaction timeout of 1 second.
|
|
myEnv.set_timeout(1000000, DB_SET_TXN_TIMEOUT);
|
|
// Configure 40 maximum transactions.
|
|
myEnv.set_tx_max(40);
|
|
myEnv.open(envHome.c_str(), env_flags, 0);
|
|
|
|
// From here, you open your databases, proceed with your
|
|
// database operations, and respond to deadlocks as
|
|
// is normal (omitted for brevity).
|
|
|
|
|
|
...</pre>
|
|
</div>
|
|
<div class="navfooter">
|
|
<hr />
|
|
<table width="100%" summary="Navigation footer">
|
|
<tr>
|
|
<td width="40%" align="left"><a accesskey="p" href="txnindices.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="txnconcurrency.html">Next</a></td>
|
|
</tr>
|
|
<tr>
|
|
<td width="40%" align="left" valign="top">Secondary Indices with Transaction Applications </td>
|
|
<td width="20%" align="center">
|
|
<a accesskey="h" href="index.html">Home</a>
|
|
</td>
|
|
<td width="40%" align="right" valign="top"> Chapter 4. Concurrency</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
</body>
|
|
</html>
|
|
|