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<!--$Id: envopen.so,v 11.12 2000/03/18 21:43:20 bostic Exp $-->
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<title>Berkeley DB Reference Guide: Release 3.0: environment open/close/unlink</title>
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<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,java,C,C++">
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<body bgcolor=white>
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<table><tr valign=top>
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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Upgrading Berkeley DB Applications</dl></h3></td>
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<td width="1%"><a href="../../ref/upgrade.3.0/intro.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../../ref/toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../../ref/upgrade.3.0/func.html"><img src="../../images/next.gif" alt="Next"></a>
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</td></tr></table>
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<p>
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<h1 align=center>Release 3.0: environment open/close/unlink</h1>
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<p>The hardest part of upgrading your application from a 2.X code base to
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the 3.0 release is translating the Berkeley DB environment open, close and
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remove calls.
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<p>There were two logical changes in this part of the Berkeley DB interface.
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First, in Berkeley DB 3.0, there are no longer separate structures that
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represent each subsystem (e.g., DB_LOCKTAB or DB_TXNMGR) and an overall
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DB_ENV environment structure. Instead there is only the
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DB_ENV structure. This means that DB_ENV references should
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be passed around by your application instead of passing around DB_LOCKTAB
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or DB_TXNMGR references. This is likely to be a simple change for most
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applications as few applications use the lock_XXX, log_XXX,
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memp_XXX or txn_XXX interfaces to create Berkeley DB environments.
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<p>The second change is that there are no longer separate open, close, and
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unlink interfaces to the
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Berkeley DB subsystems, e.g., in previous releases, it was possible to open a
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lock subsystem either using db_appinit or using the lock_open call. In
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the 3.0 release the XXX_open interfaces to the subsystems have been
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removed, and subsystems must now be opened using the 3.0 replacement for the
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db_appinit call.
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<p>To upgrade your application, first find each place your application opens,
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closes and/or removes a Berkeley DB environment. This will be code of the form:
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<p><blockquote><pre>db_appinit, db_appexit
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lock_open, lock_close, lock_unlink
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log_open, log_close, log_unlink
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memp_open, memp_close, memp_unlink
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txn_open, txn_close, txn_unlink</pre></blockquote>
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<p>Each of these groups of calls should be replaced with calls to:
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<p><blockquote><pre><a href="../../api_c/env_create.html">db_env_create</a>, <a href="../../api_c/env_open.html">DBENV->open</a>, <a href="../../api_c/env_close.html">DBENV->close</a>,
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<a href="../../api_c/env_remove.html">DBENV->remove</a></pre></blockquote>
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<p>The <a href="../../api_c/env_create.html">db_env_create</a> call and the call to the <a href="../../api_c/env_open.html">DBENV->open</a>
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method replace the db_appinit, lock_open, log_open, memp_open and txn_open
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calls. The <a href="../../api_c/env_close.html">DBENV->close</a> method replaces the db_appexit,
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lock_close, log_close, memp_close and txn_close calls. The
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<a href="../../api_c/env_remove.html">DBENV->remove</a> call replaces the lock_unlink, log_unlink,
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memp_unlink and txn_unlink calls.
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<p>Here's an example creating a Berkeley DB environment using the 2.X interface:
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<p><blockquote><pre>/*
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* db_init --
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* Initialize the environment.
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*/
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DB_ENV *
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db_init(home)
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char *home;
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{
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DB_ENV *dbenv;
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<p>
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if ((dbenv = (DB_ENV *)calloc(sizeof(DB_ENV), 1)) == NULL)
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return (errno);
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<p>
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if ((errno = db_appinit(home, NULL, dbenv,
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DB_INIT_LOCK | DB_INIT_LOG | DB_INIT_MPOOL | DB_INIT_TXN |
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DB_USE_ENVIRON)) == 0)
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return (dbenv);
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<p>
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free(dbenv);
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return (NULL);
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}</pre></blockquote>
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<p>In the Berkeley DB 3.0 release, this code would be written as:
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<p><blockquote><pre>/*
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* db_init --
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* Initialize the environment.
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*/
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int
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db_init(home, dbenvp)
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char *home;
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DB_ENV **dbenvp;
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{
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int ret;
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DB_ENV *dbenv;
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<p>
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if ((ret = db_env_create(&dbenv, 0)) != 0)
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return (ret);
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<p>
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if ((ret = dbenv->open(dbenv, home, NULL,
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DB_INIT_LOCK | DB_INIT_LOG | DB_INIT_MPOOL | DB_INIT_TXN |
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DB_USE_ENVIRON, 0)) == 0) {
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*dbenvp = dbenv;
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return (0);
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}
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<p>
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(void)dbenv->close(dbenv, 0);
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return (ret);
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}</pre></blockquote>
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<p>As you can see, the arguments to db_appinit and to <a href="../../api_c/env_open.html">DBENV->open</a> are
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largely the same. There is some minor re-organization: the mapping is
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that arguments #1, 2, 3, and 4 to db_appinit become arguments #2, 3, 1
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and 4 to <a href="../../api_c/env_open.html">DBENV->open</a>. There is one additional argument to
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<a href="../../api_c/env_open.html">DBENV->open</a>, argument #5. For backward compatibility with the 2.X
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Berkeley DB releases, simply set that argument to 0.
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<p>It is only slightly more complex to translate calls to XXX_open to the
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<a href="../../api_c/env_open.html">DBENV->open</a> method. Here's an example of creating a lock region
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using the 2.X interface:
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<p><blockquote><pre>lock_open(dir, DB_CREATE, 0664, dbenv, ®ionp);</pre></blockquote>
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<p>In the Berkeley DB 3.0 release, this code would be written as:
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<p><blockquote><pre>if ((ret = db_env_create(&dbenv, 0)) != 0)
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return (ret);
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<p>
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if ((ret = dbenv->open(dbenv,
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dir, NULL, DB_CREATE | DB_INIT_LOCK, 0664)) == 0) {
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*dbenvp = dbenv;
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return (0);
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}</pre></blockquote>
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<p>Note that in this example, you no longer need the DB_LOCKTAB structure
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reference that was required in Berkeley DB 2.X releases.
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<p>The final issue with upgrading the db_appinit call is the DB_MPOOL_PRIVATE
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option previously provided for the db_appinit interface. If your
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application is using this flag, it should almost certainly use the new
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<a href="../../api_c/env_open.html#DB_PRIVATE">DB_PRIVATE</a> flag to the <a href="../../api_c/env_open.html">DBENV->open</a> interface. Regardless,
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you should carefully consider this change before converting to use the
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<a href="../../api_c/env_open.html#DB_PRIVATE">DB_PRIVATE</a> flag.
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<p>Translating db_appexit or XXX_close calls to <a href="../../api_c/env_close.html">DBENV->close</a> is equally
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simple. Instead of taking a reference to a per-subsystem structure such
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as DB_LOCKTAB or DB_TXNMGR, all calls take a reference to a DB_ENV
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structure. The calling sequence is otherwise unchanged. Note that as
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the application no longer allocates the memory for the DB_ENV structure,
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application code to discard it after the call to db_appexit() is no longer
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needed.
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<p>Translating XXX_unlink calls to <a href="../../api_c/env_remove.html">DBENV->remove</a> is slightly more complex.
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As with <a href="../../api_c/env_close.html">DBENV->close</a>, the call takes a reference to a DB_ENV
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structure instead of a per-subsystem structure. The calling sequence is
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slightly different, however. Here is an example of removing a lock region
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using the 2.X interface:
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<p><blockquote><pre>DB_ENV *dbenv;
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<p>
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ret = lock_unlink(dir, 1, dbenv);</pre></blockquote>
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<p>In the Berkeley DB 3.0 release, this code fragment would be written as:
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<p><blockquote><pre>DB_ENV *dbenv;
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<p>
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ret = dbenv->remove(dbenv, dir, NULL, DB_FORCE);</pre></blockquote>
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<p>The additional argument to the <a href="../../api_c/env_remove.html">DBENV->remove</a> function is a
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configuration argument similar to that previously taken by db_appinit and
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now taken by the <a href="../../api_c/env_open.html">DBENV->open</a> method. For backward compatibility
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this new argument should simply be set to NULL. The force argument to
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XXX_unlink is now a flag value that is set by bitwise inclusively <b>OR</b>'ing it the
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<a href="../../api_c/env_remove.html">DBENV->remove</a> flag argument.
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<table><tr><td><br></td><td width="1%"><a href="../../ref/upgrade.3.0/intro.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../../ref/toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../../ref/upgrade.3.0/func.html"><img src="../../images/next.gif" alt="Next"></a>
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</td></tr></table>
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<p><font size=1><a href="http://www.sleepycat.com">Copyright Sleepycat Software</a></font>
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