mirror of
https://github.com/berkeleydb/libdb.git
synced 2024-11-16 17:16:25 +00:00
209 lines
6.8 KiB
HTML
209 lines
6.8 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>Transactional cursors</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="Berkeley DB Programmer's Reference Guide" />
|
||
<link rel="up" href="transapp.html" title="Chapter 11. Berkeley DB Transactional Data Store Applications" />
|
||
<link rel="prev" href="transapp_read.html" title="Degrees of isolation" />
|
||
<link rel="next" href="transapp_nested.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">Transactional cursors</th>
|
||
</tr>
|
||
<tr>
|
||
<td width="20%" align="left"><a accesskey="p" href="transapp_read.html">Prev</a> </td>
|
||
<th width="60%" align="center">Chapter 11.
|
||
Berkeley DB Transactional Data Store Applications
|
||
</th>
|
||
<td width="20%" align="right"> <a accesskey="n" href="transapp_nested.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="transapp_cursor"></a>Transactional cursors</h2>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<p>Berkeley DB cursors may be used inside a transaction, exactly as any other
|
||
<a href="../api_reference/C/db.html" class="olink">DB</a> method. The enclosing transaction ID must be specified when
|
||
the cursor is created, but it does not then need to be further specified
|
||
on operations performed using the cursor. One important point to
|
||
remember is that a cursor <span class="bold"><strong>must be closed</strong></span> before the enclosing
|
||
transaction is committed or aborted.</p>
|
||
<p>The following code fragment uses a cursor to store a new key in the cats
|
||
database with four associated data items. The key is a name. The data
|
||
items are a company name and a list of the breeds of cat owned. Each
|
||
of the data entries is stored as a duplicate data item. In this
|
||
example, transactions are necessary to ensure that either all or none
|
||
of the data items appear in case of system or application failure.</p>
|
||
<pre class="programlisting">int
|
||
main(int argc, char *argv)
|
||
{
|
||
extern int optind;
|
||
DB *db_cats, *db_color, *db_fruit;
|
||
DB_ENV *dbenv;
|
||
int ch;
|
||
|
||
while ((ch = getopt(argc, argv, "")) != EOF)
|
||
switch (ch) {
|
||
case '?':
|
||
default:
|
||
usage();
|
||
}
|
||
argc -= optind;
|
||
argv += optind;
|
||
|
||
env_dir_create();
|
||
env_open(&dbenv);
|
||
|
||
/* Open database: Key is fruit class; Data is specific type. */
|
||
db_open(dbenv, &db_fruit, "fruit", 0);
|
||
|
||
/* Open database: Key is a color; Data is an integer. */
|
||
db_open(dbenv, &db_color, "color", 0);
|
||
|
||
/*
|
||
* Open database:
|
||
* Key is a name; Data is: company name, cat breeds.
|
||
*/
|
||
db_open(dbenv, &db_cats, "cats", 1);
|
||
|
||
add_fruit(dbenv, db_fruit, "apple", "yellow delicious");
|
||
|
||
add_color(dbenv, db_color, "blue", 0);
|
||
add_color(dbenv, db_color, "blue", 3);
|
||
|
||
<span class="bold"><strong> add_cat(dbenv, db_cats,
|
||
"Amy Adams",
|
||
"Oracle",
|
||
"abyssinian",
|
||
"bengal",
|
||
"chartreaux",
|
||
NULL);</strong></span>
|
||
|
||
return (0);
|
||
}
|
||
|
||
<span class="bold"><strong>int
|
||
add_cat(DB_ENV *dbenv, DB *db, char *name, ...)
|
||
{
|
||
va_list ap;
|
||
DBC *dbc;
|
||
DBT key, data;
|
||
DB_TXN *tid;
|
||
int fail, ret, t_ret;
|
||
char *s;
|
||
|
||
/* Initialization. */
|
||
fail = 0;
|
||
|
||
memset(&key, 0, sizeof(key));
|
||
memset(&data, 0, sizeof(data));
|
||
key.data = name;
|
||
key.size = strlen(name);
|
||
|
||
retry: /* Begin the transaction. */
|
||
if ((ret = dbenv->txn_begin(dbenv, NULL, &tid, 0)) != 0) {
|
||
dbenv->err(dbenv, ret, "DB_ENV->txn_begin");
|
||
exit (1);
|
||
}
|
||
|
||
/* Delete any previously existing item. */
|
||
switch (ret = db->del(db, tid, &key, 0)) {
|
||
case 0:
|
||
case DB_NOTFOUND:
|
||
break;
|
||
case DB_LOCK_DEADLOCK:
|
||
default:
|
||
/* Retry the operation. */
|
||
if ((t_ret = tid->abort(tid)) != 0) {
|
||
dbenv->err(dbenv, t_ret, "DB_TXN->abort");
|
||
exit (1);
|
||
}
|
||
if (fail++ == MAXIMUM_RETRY)
|
||
return (ret);
|
||
goto retry;
|
||
}
|
||
|
||
/* Create a cursor. */
|
||
if ((ret = db->cursor(db, tid, &dbc, 0)) != 0) {
|
||
dbenv->err(dbenv, ret, "db->cursor");
|
||
exit (1);
|
||
}
|
||
|
||
/* Append the items, in order. */
|
||
va_start(ap, name);
|
||
while ((s = va_arg(ap, char *)) != NULL) {
|
||
data.data = s;
|
||
data.size = strlen(s);
|
||
switch (ret = dbc->put(dbc, &key, &data, DB_KEYLAST)) {
|
||
case 0:
|
||
break;
|
||
case DB_LOCK_DEADLOCK:
|
||
default:
|
||
va_end(ap);
|
||
|
||
/* Retry the operation. */
|
||
if ((t_ret = dbc->close(dbc)) != 0) {
|
||
dbenv->err(
|
||
dbenv, t_ret, "dbc->close");
|
||
exit (1);
|
||
}
|
||
if ((t_ret = tid->abort(tid)) != 0) {
|
||
dbenv->err(dbenv, t_ret, "DB_TXN->abort");
|
||
exit (1);
|
||
}
|
||
if (fail++ == MAXIMUM_RETRY)
|
||
return (ret);
|
||
goto retry;
|
||
}
|
||
}
|
||
va_end(ap);
|
||
|
||
/* Success: commit the change. */
|
||
if ((ret = dbc->close(dbc)) != 0) {
|
||
dbenv->err(dbenv, ret, "dbc->close");
|
||
exit (1);
|
||
}
|
||
if ((ret = tid->commit(tid, 0)) != 0) {
|
||
dbenv->err(dbenv, ret, "DB_TXN->commit");
|
||
exit (1);
|
||
}
|
||
return (0);
|
||
}</strong></span></pre>
|
||
</div>
|
||
<div class="navfooter">
|
||
<hr />
|
||
<table width="100%" summary="Navigation footer">
|
||
<tr>
|
||
<td width="40%" align="left"><a accesskey="p" href="transapp_read.html">Prev</a> </td>
|
||
<td width="20%" align="center">
|
||
<a accesskey="u" href="transapp.html">Up</a>
|
||
</td>
|
||
<td width="40%" align="right"> <a accesskey="n" href="transapp_nested.html">Next</a></td>
|
||
</tr>
|
||
<tr>
|
||
<td width="40%" align="left" valign="top">Degrees of isolation </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>
|