mirror of
https://github.com/yasuhirokimura/db18
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Yasuhiro KIMURA
214 lines
6.9 KiB
HTML
214 lines
6.9 KiB
HTML
<?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>Transactional cursors</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="Berkeley DB Programmer's Reference Guide" />
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<link rel="up" href="transapp.html" title="Chapter 11. Berkeley DB Transactional Data Store Applications" />
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<link rel="prev" href="transapp_read.html" title="Degrees of isolation" />
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<link rel="next" href="transapp_nested.html" title="Nested transactions" />
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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 18.1.40</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">Transactional cursors</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="transapp_read.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 11. Berkeley DB Transactional Data Store Applications </th>
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<td width="20%" align="right"> <a accesskey="n" href="transapp_nested.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="transapp_cursor"></a>Transactional cursors</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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Berkeley DB cursors may be used inside a transaction,
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exactly as any other <a href="../api_reference/C/db.html" class="olink">DB</a> method. The enclosing transaction ID
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must be specified when the cursor is created, but it does not
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then need to be further specified on operations performed
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using the cursor. One important point to remember is that a
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cursor <span class="bold"><strong>must be closed</strong></span> before
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the enclosing transaction is committed or aborted.
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</p>
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<p>
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The following code fragment uses a cursor to store a new key
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in the cats database with four associated data items. The key
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is a name. The data items are a company name and a list of the
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breeds of cat owned. Each of the data entries is stored as a
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duplicate data item. In this example, transactions are
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necessary to ensure that either all or none of the data items
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appear in case of system or application failure.
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</p>
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<pre class="programlisting">int
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main(int argc, char *argv)
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{
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extern int optind;
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DB *db_cats, *db_color, *db_fruit;
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DB_ENV *dbenv;
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int ch;
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while ((ch = getopt(argc, argv, "")) != EOF)
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switch (ch) {
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case '?':
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default:
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usage();
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}
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argc -= optind;
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argv += optind;
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env_dir_create();
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env_open(&dbenv);
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/* Open database: Key is fruit class; Data is specific type. */
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db_open(dbenv, &db_fruit, "fruit", 0);
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/* Open database: Key is a color; Data is an integer. */
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db_open(dbenv, &db_color, "color", 0);
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/*
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* Open database:
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* Key is a name; Data is: company name, cat breeds.
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*/
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db_open(dbenv, &db_cats, "cats", 1);
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add_fruit(dbenv, db_fruit, "apple", "yellow delicious");
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add_color(dbenv, db_color, "blue", 0);
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add_color(dbenv, db_color, "blue", 3);
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<span class="bold"><strong> add_cat(dbenv, db_cats,
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"Amy Adams",
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"Oracle",
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"abyssinian",
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"bengal",
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"chartreaux",
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NULL);</strong></span>
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return (0);
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}
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<span class="bold"><strong>int
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add_cat(DB_ENV *dbenv, DB *db, char *name, ...)
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{
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va_list ap;
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DBC *dbc;
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DBT key, data;
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DB_TXN *tid;
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int fail, ret, t_ret;
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char *s;
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/* Initialization. */
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fail = 0;
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memset(&key, 0, sizeof(key));
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memset(&data, 0, sizeof(data));
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key.data = name;
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key.size = strlen(name);
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retry: /* Begin the transaction. */
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if ((ret = dbenv->txn_begin(dbenv, NULL, &tid, 0)) != 0) {
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dbenv->err(dbenv, ret, "DB_ENV->txn_begin");
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exit (1);
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}
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/* Delete any previously existing item. */
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switch (ret = db->del(db, tid, &key, 0)) {
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case 0:
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case DB_NOTFOUND:
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break;
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case DB_LOCK_DEADLOCK:
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default:
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/* Retry the operation. */
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if ((t_ret = tid->abort(tid)) != 0) {
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dbenv->err(dbenv, t_ret, "DB_TXN->abort");
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exit (1);
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}
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if (fail++ == MAXIMUM_RETRY)
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return (ret);
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goto retry;
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}
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/* Create a cursor. */
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if ((ret = db->cursor(db, tid, &dbc, 0)) != 0) {
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dbenv->err(dbenv, ret, "db->cursor");
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exit (1);
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}
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/* Append the items, in order. */
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va_start(ap, name);
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while ((s = va_arg(ap, char *)) != NULL) {
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data.data = s;
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data.size = strlen(s);
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switch (ret = dbc->put(dbc, &key, &data, DB_KEYLAST)) {
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case 0:
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break;
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case DB_LOCK_DEADLOCK:
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default:
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va_end(ap);
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/* Retry the operation. */
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if ((t_ret = dbc->close(dbc)) != 0) {
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dbenv->err(
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dbenv, t_ret, "dbc->close");
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exit (1);
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}
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if ((t_ret = tid->abort(tid)) != 0) {
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dbenv->err(dbenv, t_ret, "DB_TXN->abort");
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exit (1);
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}
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if (fail++ == MAXIMUM_RETRY)
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return (ret);
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goto retry;
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}
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}
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va_end(ap);
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/* Success: commit the change. */
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if ((ret = dbc->close(dbc)) != 0) {
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dbenv->err(dbenv, ret, "dbc->close");
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exit (1);
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}
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if ((ret = tid->commit(tid, 0)) != 0) {
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dbenv->err(dbenv, ret, "DB_TXN->commit");
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exit (1);
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}
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return (0);
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}</strong></span></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="transapp_read.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="transapp.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="transapp_nested.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">Degrees of isolation </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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