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<div class="sect1" lang="en" xml:lang="en">
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<div>
<div>
<h2 class="title" style="clear: both"><a id="dbcursor"></a>Db::cursor()</h2>
</div>
</div>
</div>
<pre class="programlisting">#include <db_cxx.h>
int
Db::cursor(DbTxn *txnid, Dbc **cursorp, u_int32_t flags);</pre>
<p>
The <code class="methodname">Db::cursor()</code> method returns a created database cursor.
</p>
<p>
Cursors may span threads, but only serially, that is, the application
must serialize access to the cursor handle.
</p>
<p>
The <code class="methodname">Db::cursor()</code> <span>
<span>
method either returns a non-zero error value or throws an
exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
</span>
</span>
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1654007"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1654518"></a>cursorp</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>cursorp</strong></span> parameter references
memory into which a pointer to the allocated cursor is copied.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1654741"></a>flags</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>flags</strong></span> parameter must be set to 0
or by bitwise inclusively <span class="bold"><strong>OR</strong></span>'ing
together one or more of the following values:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p><a id="cursor_DB_BULK"></a>
<code class="literal">DB_BULK</code>
</p>
<p>
Configure a cursor to optimize for bulk operations. Each
successive operation on a cursor configured with this flag
attempts to continue on the same database page as the previous
operation, falling back to a search if a different page is
required. This avoids searching if there is a high degree of
locality between cursor operations. This flag is currently
only effective with the btree access method: for other access
methods it is ignored.
</p>
</li>
<li>
<p><a id="cursor_DB_READ_COMMITTED"></a>
<code class="literal">DB_READ_COMMITTED</code>
</p>
<p>
Configure a transactional cursor to have degree 2 isolation. This
ensures the stability of the current data item read by this cursor but
permits data read by this cursor to be modified or deleted prior to
the commit of the transaction for this cursor.
</p>
</li>
<li>
<p><a id="cursor_DB_READ_UNCOMMITTED"></a>
<code class="literal">DB_READ_UNCOMMITTED</code>
</p>
<p>
Configure a transactional cursor to have degree 1 isolation. Read
operations performed by the cursor may return modified but not yet
committed data. Silently ignored if the
<a class="link" href="dbopen.html#dbopen_DB_READ_UNCOMMITTED">DB_READ_UNCOMMITTED</a>
flag was not specified when the underlying database was opened.
</p>
</li>
<li>
<p><a id="cursor_DB_WRITECURSOR"></a>
<code class="literal">DB_WRITECURSOR</code>
</p>
<p>
Specify that the cursor will be used to update the database. The
underlying database environment must have been opened using the
<a class="link" href="envopen.html#envopen_DB_INIT_CDB">DB_INIT_CDB</a> flag.
</p>
</li>
<li>
<p><a id="cursor_DB_TXN_SNAPSHOT"></a>
<code class="literal">DB_TXN_SNAPSHOT</code>
</p>
<p>
Configure a transactional cursor to operate with read-only <a href="../../programmer_reference/transapp_read.html" class="olink">snapshot isolation</a>. For
databases with the
<a class="link" href="dbopen.html#dbopen_DB_MULTIVERSION">DB_MULTIVERSION</a>
flag set, data values will be read as they are when the cursor is
opened, without taking read locks.
</p>
<p>
This flag implicitly begins a transaction that is committed when the cursor is
closed.
</p>
<p>
This flag is silently ignored if
<a class="link" href="dbopen.html#dbopen_DB_MULTIVERSION">DB_MULTIVERSION</a>
is not set on the underlying database or if a transaction is supplied in
the <span class="bold"><strong>txnid</strong></span> parameter.
</p>
</li>
</ul>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1654901"></a>txnid</h4>
</div>
</div>
</div>
<p>
To transaction-protect cursor operations, cursors must be
opened and closed within the context of a transaction. The
<span class="bold"><strong>txnid</strong></span> parameter specifies the
transaction context in which the cursor may be used.
</p>
<p>
Cursor operations are not automatically transaction-protected, even if the
<a class="link" href="envset_flags.html#envset_flags_DB_AUTO_COMMIT">DB_AUTO_COMMIT</a>
flag is specified to the
<a class="xref" href="envset_flags.html" title="DbEnv::set_flags()">DbEnv::set_flags()</a> or
<a class="xref" href="dbopen.html" title="Db::open()">Db::open()</a> methods. If
cursor operations are to be transaction-protected, the <span class="bold"><strong>txnid</strong></span> parameter must be a transaction handle
returned from <a class="xref" href="txnbegin.html" title="DbEnv::txn_begin()">DbEnv::txn_begin()</a>; otherwise,
NULL.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1654976"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">Db::cursor()</code> <span>
<span>
method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a>
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors:
</span>
</span>
</p>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1654514"></a><span>DbRepHandleDeadException or</span> DB_REP_HANDLE_DEAD</h4>
</div>
</div>
</div>
<p>
When a client synchronizes with the master, it is possible for committed
transactions to be rolled back. This invalidates all the database and cursor
handles opened in the replication environment. Once this occurs, an attempt to use
such a handle will
<span>
throw a <a class="xref" href="dbrephandledead.html" title="DbRepHandleDeadException">DbRepHandleDeadException</a> (if
your application is configured to throw exceptions), or
</span>
return <code class="literal">DB_REP_HANDLE_DEAD</code>.
The application will need to discard the handle and open a new one in order to
continue processing.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1654706"></a><span>DbDeadlockException or </span>DB_REP_LOCKOUT</h4>
</div>
</div>
</div>
<p>
The operation was blocked by client/master synchronization.
</p>
<p>
<a class="xref" href="dbdeadlock.html" title="DbDeadlockException">DbDeadlockException</a> is thrown if
your Berkeley DB API is configured to throw exceptions.
Otherwise, <code class="literal">DB_REP_LOCKOUT</code> is returned.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1654912"></a>EINVAL</h4>
</div>
</div>
</div>
<p>
An invalid flag value or parameter was specified.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1654829"></a>Class</h3>
</div>
</div>
</div>
<p>
<a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a>
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1654806"></a>See Also</h3>
</div>
</div>
</div>
<p>
<a class="xref" href="dbc.html#dbclist" title="Database Cursors and Related Methods">Database Cursors and Related Methods</a>
</p>
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