Berkeley DB Reference Guide: Upgrading Berkeley DB Applications

Release 3.0: database open/close

Database opens were changed in the Berkeley DB 3.0 release in a similar way to environment opens.

To upgrade your application, first find each place your application opens a database, that is, calls the db_open function. Each of these calls should be replaced with calls to db_create and DB->open.

Here's an example creating a Berkeley DB database using the 2.X interface:

DB *dbp;
DB_ENV *dbenv;
int ret;

if ((ret = db_open(DATABASE,
    DB_BTREE, DB_CREATE, 0664, dbenv, NULL, &dbp)) != 0)
	return (ret);

In the Berkeley DB 3.0 release, this code would be written as:

DB *dbp;
DB_ENV *dbenv;
int ret;

if ((ret = db_create(&dbp, dbenv, 0)) != 0)
	return (ret);

if ((ret = dbp->open(dbp,
    DATABASE, NULL, DB_BTREE, DB_CREATE, 0664)) != 0) {
	(void)dbp->close(dbp, 0);
	return (ret);
}

As you can see, the arguments to db_open and to DB->open are largely the same. There is some re-organization, and note that the enclosing DB_ENV structure is specified when the DB object is created using the db_create interface. There is one additional argument to DB->open, argument #3. For backward compatibility with the 2.X Berkeley DB releases, simply set that argument to NULL.

There are two additional issues with the db_open call.

First, it was possible in the 2.X releases for an application to provide an environment that did not contain a shared memory buffer pool as the database environment, and Berkeley DB would create a private one automatically. This functionality is no longer available, applications must specify the DB_INIT_MPOOL flag if databases are going to be opened in the environment.

The final issue with upgrading the db_open call is that the DB_INFO structure is no longer used, having been replaced by individual methods on the DB handle. That change is discussed in detail later in this chapter.

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