<?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>DB_SEQUENCE->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 11. The DB_SEQUENCE Handle" /> <link rel="prev" href="seqclose.html" title="DB_SEQUENCE->close()" /> <link rel="next" href="seqget_cachesize.html" title="DB_SEQUENCE->get_cachesize()" /> </head> <body> <div xmlns="" class="navheader"> <div class="libver"> <p>Library Version 11.2.5.3</p> </div> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">DB_SEQUENCE->get()</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="seqclose.html">Prev</a> </td> <th width="60%" align="center">Chapter 11. The DB_SEQUENCE 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>DB_SEQUENCE->get()</h2> </div> </div> </div> <pre class="programlisting">#include <db.h> int DB_SEQUENCE->get(DB_SEQUENCE *seq, DB_TXN *txnid, int32_t delta, db_seq_t *retp, u_int32_t flags); </pre> <p> The <code class="methodname">DB_SEQUENCE->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">DB_SEQUENCE->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="DB_SEQUENCE->set_flags()">DB_SEQUENCE->set_flags()</a> method. </p> <p> The <code class="methodname">DB_SEQUENCE->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="idp54587600"></a>Parameters</h3> </div> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp54587792"></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="DB_ENV->txn_begin()">DB_ENV->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="DB_ENV->cdsgroup_begin()">DB_ENV->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">DB_SEQUENCE->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">DB_SEQUENCE->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">DB_SEQUENCE->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="idp54530312"></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="idp54598976"></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="idp54585448"></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="idp54594624"></a>Class</h3> </div> </div> </div> <p> <a class="link" href="seq.html" title="Chapter 11. The DB_SEQUENCE Handle">DB_SEQUENCE</a> </p> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp54590448"></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">DB_SEQUENCE->close() </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> DB_SEQUENCE->get_cachesize()</td> </tr> </table> </div> </body> </html>