mirror of
https://github.com/berkeleydb/libdb.git
synced 2024-11-17 01:26:25 +00:00
211 lines
9.6 KiB
HTML
211 lines
9.6 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
|
||
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
||
<html xmlns="http://www.w3.org/1999/xhtml">
|
||
<head>
|
||
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
|
||
<title>DbSequence::get()</title>
|
||
<link rel="stylesheet" href="apiReference.css" type="text/css" />
|
||
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
|
||
<link rel="start" href="index.html" title="Berkeley DB C++ API Reference" />
|
||
<link rel="up" href="seq.html" title="Chapter 12. The DbSequence Handle" />
|
||
<link rel="prev" href="seqclose.html" title="DbSequence::close()" />
|
||
<link rel="next" href="seqget_cachesize.html" title="DbSequence::get_cachesize()" />
|
||
</head>
|
||
<body>
|
||
<div xmlns="" class="navheader">
|
||
<div class="libver">
|
||
<p>Library Version 11.2.5.2</p>
|
||
</div>
|
||
<table width="100%" summary="Navigation header">
|
||
<tr>
|
||
<th colspan="3" align="center">DbSequence::get()</th>
|
||
</tr>
|
||
<tr>
|
||
<td width="20%" align="left"><a accesskey="p" href="seqclose.html">Prev</a> </td>
|
||
<th width="60%" align="center">Chapter 12.
|
||
The DbSequence Handle
|
||
</th>
|
||
<td width="20%" align="right"> <a accesskey="n" href="seqget_cachesize.html">Next</a></td>
|
||
</tr>
|
||
</table>
|
||
<hr />
|
||
</div>
|
||
<div class="sect1" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
|
||
<h2 class="title" style="clear: both"><a id="seqget"></a>DbSequence::get()</h2>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<pre class="programlisting">#include <db_cxx.h>
|
||
|
||
int
|
||
DbSequence::get(DbTxn *txnid, int32_t delta, db_seq_t *retp,
|
||
u_int32_t flags);</pre>
|
||
<p>
|
||
The <code class="methodname">DbSequence::get()</code> method returns the next available element in
|
||
the sequence and changes the sequence value by <span class="bold"><strong>delta</strong></span>. The value of <span class="bold"><strong>delta</strong></span> must be greater than zero. If there are
|
||
enough cached values in the sequence handle then they will be
|
||
returned. Otherwise the next value will be fetched from the database
|
||
and incremented (decremented) by enough to cover the <span class="bold"><strong>delta</strong></span> and the next batch of cached values.
|
||
</p>
|
||
<p>
|
||
For maximum concurrency a non-zero cache size should be specified
|
||
prior to opening the sequence handle and
|
||
<a class="link" href="envset_flags.html#envset_flags_DB_TXN_NOSYNC">DB_TXN_NOSYNC</a>
|
||
should be specified for each <code class="methodname">DbSequence::get()</code> method call.
|
||
</p>
|
||
<p>
|
||
By default, sequence ranges do not wrap; to cause the sequence to wrap
|
||
around the beginning or end of its range, specify the
|
||
<a class="link" href="seqset_flags.html#seqset_flags_DB_SEQ_WRAP">DB_SEQ_WRAP</a>
|
||
flag to the <a class="xref" href="seqset_flags.html" title="DbSequence::set_flags()">DbSequence::set_flags()</a>
|
||
method.
|
||
</p>
|
||
<p>
|
||
The <code class="methodname">DbSequence::get()</code> method will return EINVAL if the record in the
|
||
database is not a valid sequence record, or the sequence has reached
|
||
the beginning or end of its range and is not configured to wrap.
|
||
</p>
|
||
<div class="sect2" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
|
||
<h3 class="title"><a id="id3647994"></a>Parameters</h3>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<div class="sect3" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
|
||
<h4 class="title"><a id="id3647999"></a>txnid</h4>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<p>
|
||
If the operation is part of an application-specified transaction, the
|
||
<span class="bold"><strong>txnid</strong></span> parameter is a transaction
|
||
handle returned from <a class="xref" href="txnbegin.html" title="DbEnv::txn_begin()">DbEnv::txn_begin()</a>; if the
|
||
operation is part of a Berkeley DB Concurrent Data Store group, the
|
||
<span class="bold"><strong>txnid</strong></span> parameter is a handle returned
|
||
from <a class="xref" href="envcdsgroup_begin.html" title="DbEnv::cdsgroup_begin()">DbEnv::cdsgroup_begin()</a>;
|
||
otherwise NULL. If no transaction handle is specified, but the
|
||
operation occurs in a transactional database, the operation will be
|
||
implicitly transaction protected. No <span class="bold"><strong>txnid</strong></span> handle may be specified if the sequence
|
||
handle was opened with a non-zero cache size.
|
||
</p>
|
||
<p>
|
||
If the underlying database handle was opened in a transaction, calling
|
||
<code class="methodname">DbSequence::get()</code> may result in changes to the sequence object;
|
||
these changes will be automatically committed in a transaction
|
||
internal to the Berkeley DB library. If the thread of control calling
|
||
<code class="methodname">DbSequence::get()</code> has an active transaction, which holds locks on
|
||
the same database as the one in which the sequence object is stored,
|
||
it is possible for a thread of control calling <code class="methodname">DbSequence::get()</code> to
|
||
self-deadlock because the active transaction's locks conflict with the
|
||
internal transaction's locks. For this reason, it is often preferable
|
||
for sequence objects to be stored in their own database.
|
||
</p>
|
||
</div>
|
||
<div class="sect3" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
|
||
<h4 class="title"><a id="id3647680"></a>delta</h4>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<p>
|
||
Specifies the amount to increment or decrement the sequence.
|
||
</p>
|
||
</div>
|
||
<div class="sect3" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
|
||
<h4 class="title"><a id="id3648356"></a>retp</h4>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<p>
|
||
<span class="bold"><strong>retp</strong></span> points to the memory to hold the
|
||
return value from the sequence.
|
||
</p>
|
||
</div>
|
||
<div class="sect3" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
|
||
<h4 class="title"><a id="id3635521"></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>
|
||
<code class="literal">DB_TXN_NOSYNC</code>
|
||
</p>
|
||
<p>
|
||
If the operation is implicitly transaction protected (the <span class="bold"><strong>txnid</strong></span> argument is NULL but the operation occurs
|
||
to a transactional database), do not synchronously flush the log when
|
||
the transaction commits.
|
||
</p>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<div class="sect2" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
|
||
<h3 class="title"><a id="id3648285"></a>Class</h3>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<p>
|
||
<a class="link" href="seq.html" title="Chapter 12. The DbSequence Handle">DbSequence</a>
|
||
</p>
|
||
</div>
|
||
<div class="sect2" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
|
||
<h3 class="title"><a id="id3648219"></a>See Also</h3>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<p>
|
||
<a class="xref" href="seq.html#seqlist" title="Sequences and Related Methods">Sequences and Related Methods</a>
|
||
</p>
|
||
</div>
|
||
</div>
|
||
<div class="navfooter">
|
||
<hr />
|
||
<table width="100%" summary="Navigation footer">
|
||
<tr>
|
||
<td width="40%" align="left"><a accesskey="p" href="seqclose.html">Prev</a> </td>
|
||
<td width="20%" align="center">
|
||
<a accesskey="u" href="seq.html">Up</a>
|
||
</td>
|
||
<td width="40%" align="right"> <a accesskey="n" href="seqget_cachesize.html">Next</a></td>
|
||
</tr>
|
||
<tr>
|
||
<td width="40%" align="left" valign="top">DbSequence::close() </td>
|
||
<td width="20%" align="center">
|
||
<a accesskey="h" href="index.html">Home</a>
|
||
</td>
|
||
<td width="40%" align="right" valign="top"> DbSequence::get_cachesize()</td>
|
||
</tr>
|
||
</table>
|
||
</div>
|
||
</body>
|
||
</html>
|