Import BSDDB 4.7.25 (as of svn r89086)
This commit is contained in:
Zachary Ware
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docs/gsg_txn/C/autocommit.html
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231
docs/gsg_txn/C/autocommit.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>Auto Commit</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 V1.62.4" />
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<link rel="home" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" />
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<link rel="up" href="usingtxns.html" title="Chapter 3. Transaction Basics" />
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<link rel="previous" href="abortresults.html" title="Aborting a Transaction" />
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<link rel="next" href="nestedtxn.html" title="Nested Transactions" />
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</head>
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<body>
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<div class="navheader">
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Auto Commit</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="abortresults.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 3. Transaction Basics</th>
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<td width="20%" align="right"> <a accesskey="n" href="nestedtxn.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="autocommit"></a>Auto Commit</h2>
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</div>
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</div>
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<div></div>
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</div>
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<p>
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While transactions are frequently used to provide atomicity to
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multiple database
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operations, it is sometimes necessary to perform
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a single database
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operation under the control of a transaction.
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Rather than force you to obtain a transaction, perform the single
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write operation, and then either commit or abort the transaction,
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you can automatically group this sequence of events using
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<span class="emphasis"><em>auto commit</em></span>.
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</p>
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<p>
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To use auto commit:
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</p>
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<div class="orderedlist">
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<ol type="1">
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<li>
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<p>
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Open your environment and your databases
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so that they support
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transactions. See <a href="enabletxn.html">Enabling Transactions</a>
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for details.
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</p>
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<p>
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Note that frequently auto commit is used for the environment
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or database open. To use auto commit for either your
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environment or database open, specify
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<tt class="literal">DB_AUTO_COMMIT</tt> to the
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<tt class="methodname">DB_ENV->set_flags()</tt>
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or
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<tt class="methodname">DB->open()</tt>
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method. If you specify auto commit for the environment
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open, then you do not need to also specify auto commit
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for the database open.
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</p>
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</li>
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<li>
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<p>
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Do not provide a transactional handle to the method that is
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performing the database
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write operation.
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</p>
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</li>
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</ol>
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</div>
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<p>
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Note that auto commit is not available for cursors. You must always
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open your cursor using a transaction if you want the cursor's
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operations to be transactional protected. See
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<a href="txncursor.html">Transactional Cursors</a> for details on using
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transactional cursors.
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</p>
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<p>
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For example, the following uses auto commit to perform the database write operation:
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</p>
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<pre class="programlisting">#include <stdio.h>
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#include <stdlib.h>
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#include "db.h"
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int
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main(void)
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{
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int ret, ret_c;
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u_int32_t db_flags, env_flags;
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DB *dbp;
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DB_ENV *envp;
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DBT key, data;
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const char *db_home_dir = "/tmp/myEnvironment";
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const char *file_name = "mydb.db";
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const char *keystr ="thekey";
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const char *datastr = "thedata";
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dbp = NULL;
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envp = NULL;
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/* Open the environment */
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ret = db_env_create(&envp, 0);
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if (ret != 0) {
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fprintf(stderr, "Error creating environment handle: %s\n",
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db_strerror(ret));
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return (EXIT_FAILURE);
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}
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env_flags = DB_CREATE | /* Create the environment if it does
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* not already exist. */
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DB_INIT_TXN | /* Initialize transactions */
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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 in-memory cache. */
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ret = envp->open(envp, db_home_dir, env_flags, 0);
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if (ret != 0) {
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fprintf(stderr, "Error opening environment: %s\n",
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db_strerror(ret));
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goto err;
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}
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/* Initialize the DB handle */
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ret = db_create(&dbp, envp, 0);
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if (ret != 0) {
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envp->err(envp, ret, "Database creation failed");
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goto err;
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}
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db_flags = DB_CREATE | DB_AUTO_COMMIT;
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/*
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* Open the database. Note that we are using auto commit for the open,
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* so the database is able to support transactions.
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*/
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ret = dbp->open(dbp, /* Pointer to the database */
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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 */
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if (ret != 0) {
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envp->err(envp, ret, "Database '%s' open failed",
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file_name);
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goto err;
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}
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/* Prepare the DBTs */
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memset(&key, 0, sizeof(DBT));
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memset(&data, 0, sizeof(DBT));
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key.data = &keystr;
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key.size = strlen(keystr) + 1;
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data.data = &datastr;
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data.size = strlen(datastr) + 1;
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/*
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* Perform the database write. A txn handle is not provided, but the
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* database support auto commit, so auto commit is used for the write.
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*/
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ret = dbp->put(dbp, NULL, &key, &data, 0);
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if (ret != 0) {
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envp->err(envp, ret, "Database put failed.");
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goto err;
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}
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err:
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/* Close the database */
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if (dbp != NULL) {
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ret_c = dbp->close(dbp, 0);
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if (ret_c != 0) {
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envp->err(envp, ret_c, "Database close failed.");
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ret = ret_c
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}
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}
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/* Close the environment */
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if (envp != NULL) {
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ret_c = envp->close(envp, 0);
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if (ret_c != 0) {
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fprintf(stderr, "environment close failed: %s\n",
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db_strerror(ret_c));
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ret = ret_c;
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}
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}
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return (ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE);
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} </pre>
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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="abortresults.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="usingtxns.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="nestedtxn.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">Aborting a Transaction </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"> Nested Transactions</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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