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<p>Database opens were changed in the Berkeley DB 3.0 release in a similar way to
environment opens.</p>
<p>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 <a href="../api_reference/C/dbcreate.html" class="olink">db_create()</a> and <a href="../api_reference/C/dbopen.html" class="olink">DB->open()</a>.</p>
<p>Here's an example creating a Berkeley DB database using the 2.X interface:</p>
<pre class="programlisting">DB *dbp;
DB_ENV *dbenv;
int ret;
if ((ret = db_open(DATABASE,
DB_BTREE, DB_CREATE, 0664, dbenv, NULL, &dbp)) != 0)
return (ret);</pre>
<p>In the Berkeley DB 3.0 release, this code would be written as:</p>
<pre class="programlisting">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);
}</pre>
<p>As you can see, the arguments to db_open and to <a href="../api_reference/C/dbopen.html" class="olink">DB->open()</a> are
largely the same. There is some re-organization, and note that the
enclosing <a href="../api_reference/C/env.html" class="olink">DB_ENV</a> structure is specified when the <a href="../api_reference/C/db.html" class="olink">DB</a> object
is created using the <a href="../api_reference/C/dbcreate.html" class="olink">db_create()</a> function. There is one
additional argument to <a href="../api_reference/C/dbopen.html" class="olink">DB->open()</a>, argument #3. For backward
compatibility with the 2.X Berkeley DB releases, simply set that argument to
NULL.</p>
<p>There are two additional issues with the db_open call.</p>
<p>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
<a href="../api_reference/C/envopen.html#envopen_DB_INIT_MPOOL" class="olink">DB_INIT_MPOOL</a> flag if databases are going to be opened in the
environment.</p>
<p>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structure is no longer used, having been replaced by individual methods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 <a href="../api_reference/C/db.html" class="olink">DB</a> handle. That change is discussed in detail later in
this chapter.</p>
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