mirror of
https://github.com/berkeleydb/libdb.git
synced 2024-11-16 17:16:25 +00:00
198 lines
7.7 KiB
HTML
198 lines
7.7 KiB
HTML
<?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>Auto Commit</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="abortresults.html" title="Aborting a Transaction" />
|
||
<link rel="next" href="nestedtxn.html" title="Nested Transactions" />
|
||
</head>
|
||
<body>
|
||
<div xmlns="" class="navheader">
|
||
<div class="libver">
|
||
<p>Library Version 11.2.5.3</p>
|
||
</div>
|
||
<table width="100%" summary="Navigation header">
|
||
<tr>
|
||
<th colspan="3" align="center">Auto Commit</th>
|
||
</tr>
|
||
<tr>
|
||
<td width="20%" align="left"><a accesskey="p" href="abortresults.html">Prev</a> </td>
|
||
<th width="60%" align="center">Chapter 3. Transaction Basics</th>
|
||
<td width="20%" align="right"> <a accesskey="n" href="nestedtxn.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="autocommit"></a>Auto Commit</h2>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<p>
|
||
While transactions are frequently used to provide atomicity to
|
||
multiple database
|
||
|
||
operations, it is sometimes necessary to perform
|
||
a single database
|
||
|
||
operation under the control of a transaction.
|
||
Rather than force you to obtain a transaction, perform the single
|
||
write operation, and then either commit or abort the transaction,
|
||
you can automatically group this sequence of events using
|
||
<span class="emphasis"><em>auto commit</em></span>.
|
||
</p>
|
||
<p>
|
||
To use auto commit:
|
||
</p>
|
||
<div class="orderedlist">
|
||
<ol type="1">
|
||
<li>
|
||
<p>
|
||
Open your environment and your databases
|
||
|
||
so that they support
|
||
transactions. See <a class="xref" href="enabletxn.html" title="Chapter 2. Enabling Transactions">Enabling Transactions</a>
|
||
for details.
|
||
</p>
|
||
<p>
|
||
Note that frequently auto commit is used for the environment
|
||
or database open. To use auto commit for either your
|
||
environment or database open, specify
|
||
<code class="literal">DB_AUTO_COMMIT</code> to the
|
||
|
||
|
||
<code class="methodname">DbEnv::set_flags()</code>
|
||
or
|
||
|
||
<code class="methodname">Db::open()</code>
|
||
method. If you specify auto commit for the environment
|
||
open, then you do not need to also specify auto commit
|
||
for the database open.
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
Do not provide a transactional handle to the method that is
|
||
performing the database
|
||
|
||
write operation.
|
||
</p>
|
||
</li>
|
||
</ol>
|
||
</div>
|
||
<p>
|
||
Note that auto commit is not available for cursors. You must always
|
||
open your cursor using a transaction if you want the cursor's
|
||
operations to be transactional protected. See
|
||
<a class="xref" href="txncursor.html" title="Transactional Cursors">Transactional Cursors</a> for details on using
|
||
transactional cursors.
|
||
</p>
|
||
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
|
||
<h3 class="title">Note</h3>
|
||
<p>
|
||
Never have more than one active transaction in your thread
|
||
at a time. This is especially a problem if you mix an
|
||
explicit transaction with another operation that uses auto
|
||
commit. Doing so can result in undetectable deadlocks.
|
||
</p>
|
||
</div>
|
||
<p>
|
||
For example, the following uses auto commit to perform the database write operation:
|
||
</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_INIT_TXN; // Initialize transactions
|
||
|
||
u_int32_t db_flags = DB_CREATE | DB_AUTO_COMMIT;
|
||
Db *dbp = NULL;
|
||
const char *file_name = "mydb.db";
|
||
const char *keystr ="thekey";
|
||
const char *datastr = "thedata";
|
||
|
||
std::string envHome("/export1/testEnv");
|
||
DbEnv myEnv(0);
|
||
|
||
try {
|
||
|
||
myEnv.open(envHome.c_str(), env_flags, 0);
|
||
dbp = new Db(&myEnv, 0);
|
||
|
||
// Open the database. Note that we are using auto commit for
|
||
// the open, so the database is able to support transactions.
|
||
dbp->open(NULL, // Txn pointer
|
||
file_name, // File name
|
||
NULL, // Logical db name */
|
||
DB_BTREE, // Database type (using btree)
|
||
db_flags, // Open flags
|
||
0); // File mode. Using defaults
|
||
|
||
Dbt key, data;
|
||
key.set_data(keystr);
|
||
key.set_size((strlen(keystr) + 1) * sizeof(char));
|
||
key.set_data(datastr);
|
||
key.set_size((strlen(datastr) + 1) * sizeof(char));
|
||
|
||
// Perform the write. Because the database was opened to support
|
||
// auto commit, this write is performed using auto commit.
|
||
db->put(NULL, &key, &data, 0);
|
||
|
||
} catch(DbException &e) {
|
||
std::cerr << "Error opening database and environment: "
|
||
<< file_name << ", "
|
||
<< envHome << std::endl;
|
||
std::cerr << e.what() << std::endl;
|
||
}
|
||
|
||
try {
|
||
if (dbp != NULL)
|
||
dbp->close(0);
|
||
myEnv.close(0);
|
||
} catch(DbException &e) {
|
||
std::cerr << "Error closing database and environment: "
|
||
<< file_name << ", "
|
||
<< envHome << std::endl;
|
||
std::cerr << e.what() << std::endl;
|
||
return (EXIT_FAILURE);
|
||
}
|
||
|
||
return (EXIT_SUCCESS);
|
||
} </pre>
|
||
</div>
|
||
<div class="navfooter">
|
||
<hr />
|
||
<table width="100%" summary="Navigation footer">
|
||
<tr>
|
||
<td width="40%" align="left"><a accesskey="p" href="abortresults.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="nestedtxn.html">Next</a></td>
|
||
</tr>
|
||
<tr>
|
||
<td width="40%" align="left" valign="top">Aborting a Transaction </td>
|
||
<td width="20%" align="center">
|
||
<a accesskey="h" href="index.html">Home</a>
|
||
</td>
|
||
<td width="40%" align="right" valign="top"> Nested Transactions</td>
|
||
</tr>
|
||
</table>
|
||
</div>
|
||
</body>
|
||
</html>
|