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197 lines
7.2 KiB
HTML
197 lines
7.2 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>Opening a Transactional Environment and Database</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="Getting Started with Berkeley DB Transaction Processing" />
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<link rel="up" href="enabletxn.html" title="Chapter 2. Enabling Transactions" />
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<link rel="prev" href="enabletxn.html" title="Chapter 2. Enabling Transactions" />
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<link rel="next" href="usingtxns.html" title="Chapter 3. Transaction Basics" />
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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">Opening a Transactional Environment and
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<span xmlns="http://www.w3.org/1999/xhtml">Database</span>
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</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="enabletxn.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 2. Enabling Transactions</th>
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<td width="20%" align="right"> <a accesskey="n" href="usingtxns.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="envopen"></a>Opening a Transactional Environment and
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<span>Database</span>
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</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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To enable transactions for your environment, you must initialize the
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transactional subsystem. Note that doing this also initializes the
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logging subsystem. In addition, you must initialize the memory pool
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(in-memory cache). You must also initialize the locking subsystem.
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<span>
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For example:
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</span>
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</p>
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<pre class="programlisting">#include "db_cxx.h"
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...
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int main(void)
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{
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u_int32_t env_flags = DB_CREATE | // If the environment does not
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// exist, create it.
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DB_INIT_LOCK | // Initialize locking
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DB_INIT_LOG | // Initialize logging
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DB_INIT_MPOOL | // Initialize the cache
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DB_INIT_TXN; // Initialize transactions
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std::string envHome("/export1/testEnv");
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DbEnv myEnv(0);
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try {
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myEnv.open(envHome.c_str(), env_flags, 0);
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} catch(DbException &e) {
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std::cerr << "Error opening database environment: "
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<< envHome << std::endl;
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std::cerr << e.what() << std::endl;
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return (EXIT_FAILURE);
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}
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try {
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myEnv.close(0);
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} catch(DbException &e) {
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std::cerr << "Error closing database environment: "
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<< envHome << std::endl;
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std::cerr << e.what() << std::endl;
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return (EXIT_FAILURE);
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}
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return (EXIT_SUCCESS);
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} </pre>
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<p>
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You then create and open your database(s) as you would for a non-transactional system.
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<span>
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The only difference is that you must pass the environment handle to
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the
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<span>
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<code class="methodname">DbEnv::open()</code> method,
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</span>
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and you must open the database within a transaction.
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Typically auto commit is used for this purpose. To do so, pass
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<code class="literal">DB_AUTO_COMMIT</code> to the database open command.
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It is recommended that you close all your databases before you close
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your environment.
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For example:
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</span>
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</p>
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<pre class="programlisting">#include "db_cxx.h"
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...
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int main(void)
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{
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u_int32_t env_flags = DB_CREATE | // If the environment does not
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// exist, create it.
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DB_INIT_LOCK | // Initialize locking
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DB_INIT_LOG | // Initialize logging
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DB_INIT_MPOOL | // Initialize the cache
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DB_INIT_TXN; // Initialize transactions
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<strong class="userinput"><code>u_int32_t db_flags = DB_CREATE | DB_AUTO_COMMIT;
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Db *dbp = NULL;
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const char *file_name = "mydb.db";</code></strong>
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std::string envHome("/export1/testEnv");
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DbEnv myEnv(0);
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try {
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myEnv.open(envHome.c_str(), env_flags, 0);
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<strong class="userinput"><code>dbp = new Db(&myEnv, 0);
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dbp->open(NULL, // Txn pointer
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file_name, // File name
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NULL, // Logical db name
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DB_BTREE, // Database type (using btree)
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db_flags, // Open flags
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0); // File mode. Using defaults </code></strong>
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} catch(DbException &e) {
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std::cerr << "Error opening database and environment: "
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<< file_name << ", "
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<< envHome << std::endl;
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std::cerr << e.what() << std::endl;
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}
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try {
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<strong class="userinput"><code>dbp->close(0);</code></strong>
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myEnv.close(0);
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} catch(DbException &e) {
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std::cerr << "Error closing database and environment: "
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<< file_name << ", "
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<< envHome << std::endl;
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std::cerr << e.what() << std::endl;
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return (EXIT_FAILURE);
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}
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return (EXIT_SUCCESS);
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} </pre>
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<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
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<h3 class="title">Note</h3>
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<p>
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Never close a database that has active transactions. Make sure
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all transactions are resolved (either committed or aborted)
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before closing the database.
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</p>
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</div>
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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="enabletxn.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="enabletxn.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="usingtxns.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 2. Enabling Transactions </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"> Chapter 3. Transaction Basics</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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