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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Transaction Protected Applications</dl></h3></td>
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<p>
<h1 align=center>Opening the databases</h1>
<p>Next, we open three databases ("color" and "fruit" and "cats"), in the
database environment.  Again, our DB database handles are
declared to be free-threaded using the <a href="../../api_c/env_open.html#DB_THREAD">DB_THREAD</a> flag, and so
may be used by any number of threads we subsequently create.
<p><blockquote><pre>int
main(int argc, char *argv)
{
	extern char *optarg;
	extern int optind;
	DB *db_cats, *db_color, *db_fruit;
	DB_ENV *dbenv;
	pthread_t ptid;
	int ch;
<p>
	while ((ch = getopt(argc, argv, "")) != EOF)
		switch (ch) {
		case '?':
		default:
			usage();
		}
	argc -= optind;
	argv += optind;
<p>
	env_dir_create();
	env_open(&dbenv);
<p>
<b>	/* Open database: Key is fruit class; Data is specific type. */
	db_open(dbenv, &db_fruit, "fruit", 0);
<p>
	/* Open database: Key is a color; Data is an integer. */
	db_open(dbenv, &db_color, "color", 0);
<p>
	/*
	 * Open database:
	 *	Key is a name; Data is: company name, address, cat breeds.
	 */
	db_open(dbenv, &db_cats, "cats", 1);</b>
<p>
	return (0);
}
<p>
<b>void
db_open(DB_ENV *dbenv, DB **dbp, char *name, int dups)
{
	DB *db;
	int ret;
<p>
	/* Create the database handle. */
	if ((ret = db_create(&db, dbenv, 0)) != 0) {
		dbenv-&gt;err(dbenv, ret, "db_create");
		exit (1);
	}
<p>
	/* Optionally, turn on duplicate data items. */
	if (dups && (ret = db-&gt;set_flags(db, DB_DUP)) != 0) {
		dbenv-&gt;err(dbenv, ret, "db-&gt;set_flags: DB_DUP");
		exit (1);
	}
<p>
	/*
	 * Open a database in the environment:
	 *	create if it doesn't exist
	 *	free-threaded handle
	 *	read/write owner only
	 */
	if ((ret = db-&gt;open(db, name, NULL,
	    DB_BTREE, DB_CREATE | DB_THREAD, S_IRUSR | S_IWUSR)) != 0) {
		dbenv-&gt;err(dbenv, ret, "db-&gt;open: %s", name);
		exit (1);
	}
<p>
	*dbp = db;
}</b></pre></blockquote>
<p>There is no reason to wrap database opens inside of transactions.  All
database opens are transaction protected internally to Berkeley DB, and
applications using transaction-protected environments can simply rely on
files either being successfully re-created in a recovered environment,
or not appearing at all.
<p>After running this initial code, we can use the <a href="../../utility/db_stat.html">db_stat</a> utility
to display information about a database we have created:
<p><blockquote><pre>prompt&gt; db_stat -h TXNAPP -d color
53162   Btree magic number.
8       Btree version number.
Flags:
2       Minimum keys per-page.
8192    Underlying database page size.
1       Number of levels in the tree.
0       Number of unique keys in the tree.
0       Number of data items in the tree.
0       Number of tree internal pages.
0       Number of bytes free in tree internal pages (0% ff).
1       Number of tree leaf pages.
8166    Number of bytes free in tree leaf pages (0.% ff).
0       Number of tree duplicate pages.
0       Number of bytes free in tree duplicate pages (0% ff).
0       Number of tree overflow pages.
0       Number of bytes free in tree overflow pages (0% ff).
0       Number of pages on the free list.</pre></blockquote>
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