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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 DB_THREAD flag, and so may be used by any number of threads we subsequently create.
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;
	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, address, cat breeds.
	 */
	db_open(dbenv, &db_cats, "cats", 1);
	return (0);
}
void
db_open(DB_ENV *dbenv, DB **dbp, char *name, int dups)
{
	DB *db;
	int ret;
	/* Create the database handle. */
	if ((ret = db_create(&db, dbenv, 0)) != 0) {
		dbenv->err(dbenv, ret, "db_create");
		exit (1);
	}
	/* Optionally, turn on duplicate data items. */
	if (dups && (ret = db->set_flags(db, DB_DUP)) != 0) {
		dbenv->err(dbenv, ret, "db->set_flags: DB_DUP");
		exit (1);
	}
	/*
	 * Open a database in the environment:
	 *	create if it doesn't exist
	 *	free-threaded handle
	 *	read/write owner only
	 */
	if ((ret = db->open(db, name, NULL,
	    DB_BTREE, DB_CREATE | DB_THREAD, S_IRUSR | S_IWUSR)) != 0) {
		dbenv->err(dbenv, ret, "db->open: %s", name);
		exit (1);
	}
	*dbp = db;
}
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.
After running this initial code, we can use the db_stat utility to display information about a database we have created:
prompt> 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.
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