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194 lines
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>environment open/close/unlink</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Berkeley DB Upgrade Guide" />
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<link rel="up" href="upgrade_3_0_toc.html" title="Chapter 14. Upgrading Berkeley DB 2.X applications to Berkeley DB 3.0" />
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<link rel="prev" href="upgrade_3_0_toc.html" title="Chapter 14. Upgrading Berkeley DB 2.X applications to Berkeley DB 3.0" />
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<link rel="next" href="upgrade_3_0_func.html" title="function arguments" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 11.2.5.2</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">environment open/close/unlink</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="upgrade_3_0_toc.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 14. Upgrading Berkeley DB 2.X applications to Berkeley DB 3.0</th>
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<td width="20%" align="right"> <a accesskey="n" href="upgrade_3_0_func.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="upgrade_3_0_envopen"></a>environment open/close/unlink</h2>
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</div>
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</div>
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</div>
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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.</p>
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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 (for example, DB_LOCKTAB or DB_TXNMGR) and an
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overall <a href="../api_reference/C/env.html" class="olink">DB_ENV</a> environment structure. Instead there is only the
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<a href="../api_reference/C/env.html" class="olink">DB_ENV</a> references should be passed around by your application instead of passing around
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DB_LOCKTAB or DB_TXNMGR references. This is likely to be a simple
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change for most applications as few applications use the lock_XXX,
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log_XXX, memp_XXX or txn_XXX interfaces to create Berkeley DB environments.</p>
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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 Berkeley DB subsystems. For example, in previous
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releases, it was possible to open a lock subsystem either using
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db_appinit or using the lock_open call. In the 3.0 release the XXX_open
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interfaces to the subsystems have been removed, and subsystems must now
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be opened using the 3.0 replacement for the db_appinit call.</p>
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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:</p>
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<pre class="programlisting">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>
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<p>Each of these groups of calls should be replaced with calls to
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<a href="../api_reference/C/envcreate.html" class="olink">db_env_create()</a>, <a href="../api_reference/C/envopen.html" class="olink">DB_ENV->open()</a>, <a href="../api_reference/C/envclose.html" class="olink">DB_ENV->close()</a>, and <a href="../api_reference/C/envremove.html" class="olink">DB_ENV->remove()</a>.
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</p>
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<p>The <a href="../api_reference/C/envcreate.html" class="olink">db_env_create()</a> call and the call to the <a href="../api_reference/C/envopen.html" class="olink">DB_ENV->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_reference/C/envclose.html" class="olink">DB_ENV->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_reference/C/envremove.html" class="olink">DB_ENV->remove()</a> call replaces the lock_unlink, log_unlink,
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memp_unlink and txn_unlink calls.</p>
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<p>Here's an example creating a Berkeley DB environment using the 2.X interface:</p>
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<pre class="programlisting">/*
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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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if ((dbenv = (DB_ENV *)calloc(sizeof(DB_ENV), 1)) == NULL)
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return (errno);
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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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free(dbenv);
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return (NULL);
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}</pre>
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<p>In the Berkeley DB 3.0 release, this code would be written as:</p>
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<pre class="programlisting">/*
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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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if ((ret = db_env_create(&dbenv, 0)) != 0)
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return (ret);
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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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(void)dbenv->close(dbenv, 0);
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return (ret);
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}</pre>
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<p>As you can see, the arguments to db_appinit and to <a href="../api_reference/C/envopen.html" class="olink">DB_ENV->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_reference/C/envopen.html" class="olink">DB_ENV->open()</a>. There is one additional argument to
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<a href="../api_reference/C/envopen.html" class="olink">DB_ENV->open()</a>, argument #5. For backward compatibility with the 2.X
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Berkeley DB releases, simply set that argument to 0.</p>
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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_reference/C/envopen.html" class="olink">DB_ENV->open()</a> method. Here's an example of creating a lock region
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using the 2.X interface:</p>
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<pre class="programlisting">lock_open(dir, DB_CREATE, 0664, dbenv, &regionp);</pre>
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<p>In the Berkeley DB 3.0 release, this code would be written as:</p>
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<pre class="programlisting">if ((ret = db_env_create(&dbenv, 0)) != 0)
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return (ret);
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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>
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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.</p>
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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 call. If your application
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is using this flag, it should almost certainly use the new
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<a href="../api_reference/C/envopen.html#envopen_DB_PRIVATE" class="olink">DB_PRIVATE</a> flag to the <a href="../api_reference/C/envopen.html" class="olink">DB_ENV->open()</a> method. Regardless, you
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should carefully consider this change before converting to use the
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<a href="../api_reference/C/envopen.html#envopen_DB_PRIVATE" class="olink">DB_PRIVATE</a> flag.</p>
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<p>Translating db_appexit or XXX_close calls to <a href="../api_reference/C/envclose.html" class="olink">DB_ENV->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 <a href="../api_reference/C/env.html" class="olink">DB_ENV</a>
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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.</p>
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<p>Translating XXX_unlink calls to <a href="../api_reference/C/envremove.html" class="olink">DB_ENV->remove()</a> is slightly more complex.
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As with <a href="../api_reference/C/envclose.html" class="olink">DB_ENV->close()</a>, the call takes a reference to a <a href="../api_reference/C/env.html" class="olink">DB_ENV</a>
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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:</p>
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<pre class="programlisting">DB_ENV *dbenv;
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ret = lock_unlink(dir, 1, dbenv);</pre>
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<p>In the Berkeley DB 3.0 release, this code fragment would be written as:</p>
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<pre class="programlisting">DB_ENV *dbenv;
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ret = dbenv->remove(dbenv, dir, NULL, DB_FORCE);</pre>
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<p>The additional argument to the <a href="../api_reference/C/envremove.html" class="olink">DB_ENV->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_reference/C/envopen.html" class="olink">DB_ENV->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 <span class="bold"><strong>OR</strong></span>'ing it the
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<a href="../api_reference/C/envremove.html" class="olink">DB_ENV->remove()</a> flag argument.</p>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="upgrade_3_0_toc.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="upgrade_3_0_toc.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="upgrade_3_0_func.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Chapter 14. Upgrading Berkeley DB 2.X applications to Berkeley DB 3.0 </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> function arguments</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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