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HTML
363 lines
16 KiB
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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>DB_MPOOLFILE->get()</title>
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<link rel="stylesheet" href="apiReference.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 C API Reference" />
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<link rel="up" href="memp.html" title="Chapter 8. The DB_MPOOLFILE Handle" />
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<link rel="prev" href="mempfclose.html" title="DB_MPOOLFILE->close()" />
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<link rel="next" href="mempfopen.html" title="DB_MPOOLFILE->open()" />
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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">DB_MPOOLFILE->get()</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="mempfclose.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 8.
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The DB_MPOOLFILE Handle
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="mempfopen.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="mempfget"></a>DB_MPOOLFILE->get()</h2>
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</div>
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</div>
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</div>
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<pre class="programlisting">#include <db.h>
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int
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DB_MPOOLFILE->get(DB_MPOOLFILE *mpf,
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db_pgno_t *pgnoaddr, DB_TXN * txnid, u_int32_t flags, void **pagep); </pre>
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<p>
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The <code class="methodname">DB_MPOOLFILE->get()</code> method returns pages from the cache.
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</p>
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<p>
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All pages returned by <code class="methodname">DB_MPOOLFILE->get()</code> will be retained (that is,
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<span class="emphasis"><em>latched</em></span>) in the cache until a subsequent call to
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<a class="xref" href="mempput.html" title="DB_MPOOLFILE->put()">DB_MPOOLFILE->put()</a>.
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There is no deadlock detection among latches so care must be taken in the application if the DB_MPOOL_DIRTY
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or DB_MPOOL_EDIT flags are used as these get exlusive latches on the pages.
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</p>
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<p>
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The returned page is <span class="bold"><strong>size_t</strong></span> type
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aligned.
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</p>
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<p>
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Fully or partially created pages have all their bytes set to a nul
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byte, unless the
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<a class="xref" href="mempset_clear_len.html" title="DB_MPOOLFILE->set_clear_len()">DB_MPOOLFILE->set_clear_len()</a>
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method was called to specify other behavior before the file was
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opened.
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</p>
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<p><a id="fget_DB_PAGE_NOTFOUND"></a>
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The <code class="methodname">DB_MPOOLFILE->get()</code> method will return
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<code class="literal">DB_PAGE_NOTFOUND</code> if the requested page does not exist and DB_MPOOL_CREATE
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was not set. Unless otherwise specified, the <code class="methodname">DB_MPOOLFILE->get()</code>
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<span>
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<span>
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method returns a non-zero error value on failure and 0 on success.
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</span>
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</span>
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</p>
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<div class="sect2" 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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<h3 class="title"><a id="id3917172"></a>Parameters</h3>
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</div>
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</div>
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</div>
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<div class="sect3" 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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<h4 class="title"><a id="id3917161"></a>flags</h4>
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</div>
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</div>
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</div>
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<p>
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The <span class="bold"><strong>flags</strong></span> parameter must be set to 0
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or by bitwise inclusively <span class="bold"><strong>OR</strong></span>'ing
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together one or more of the following values:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p><a id="mpoolfget_DB_MPOOL_CREATE"></a>
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<code class="literal">DB_MPOOL_CREATE</code>
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</p>
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<p>
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If the specified page does not exist, create it. In this case, the
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<a class="link" href="mempregister.html" title="DB_ENV->memp_register()">pgin</a> method, if
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specified, is called.
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</p>
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</li>
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<li>
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<p><a id="fget_DB_MPOOL_DIRTY"></a>
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<code class="literal">DB_MPOOL_DIRTY</code>
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</p>
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<p>
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The page will be modified and must be written to the source file
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before being evicted from the cache. For files open with the
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<a class="link" href="dbopen.html#dbopen_DB_MULTIVERSION">DB_MULTIVERSION</a>
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flag set, a new copy of the page will be made if this is the first
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time the specified transaction is modifying it.
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A page fetched with the <code class="literal">DB_MPOOL_DIRTY</code> flag will be
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<span class="bold"><strong>exclusively latched</strong></span> until
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a subsequent call to <a class="xref" href="mempput.html" title="DB_MPOOLFILE->put()">DB_MPOOLFILE->put()</a>.
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</p>
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</li>
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<li>
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<p><a id="fget_DB_MPOOL_EDIT"></a>
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<code class="literal">DB_MPOOL_EDIT</code>
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</p>
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<p>
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The page will be modified and must be written to the source file
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before being evicted from the cache. No copy of the page will be made,
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regardless of the
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<a class="link" href="dbopen.html#dbopen_DB_MULTIVERSION">DB_MULTIVERSION</a>
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setting. This flag is only intended for use in situations where a
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transaction handle is not available, such as during aborts or
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recovery.
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A page fetched with the <code class="literal">DB_MPOOL_EDIT</code> flag will be
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<span class="bold"><strong>exclusively latched</strong></span> until
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a subsequent call to <a class="xref" href="mempput.html" title="DB_MPOOLFILE->put()">DB_MPOOLFILE->put()</a>.
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</p>
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</li>
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<li>
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<p><a id="fget_DB_MPOOL_LAST"></a>
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<code class="literal">DB_MPOOL_LAST</code>
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</p>
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<p>
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Return the last page of the source file, and copy its page number into
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the memory location to which <span class="bold"><strong>pgnoaddr</strong></span>
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refers.
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</p>
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</li>
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<li>
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<p><a id="mpoolfget_DB_MPOOL_NEW"></a>
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<code class="literal">DB_MPOOL_NEW</code>
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</p>
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<p>
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Create a new page in the file, and copy its page number into the
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memory location to which <span class="bold"><strong>pgnoaddr</strong></span>
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refers. In this case, the <code class="literal">pgin_fcn</code> callback, if specified on
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<a class="xref" href="mempregister.html" title="DB_ENV->memp_register()">DB_ENV->memp_register()</a>, is
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<span class="bold"><strong>not</strong></span> called.
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</p>
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</li>
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</ul>
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</div>
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<p>
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The <code class="literal">DB_MPOOL_CREATE</code>, <code class="literal">DB_MPOOL_LAST</code>, and
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<code class="literal">DB_MPOOL_NEW</code> flags are mutually exclusive.
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</p>
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</div>
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<div class="sect3" 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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<h4 class="title"><a id="id3917260"></a>pagep</h4>
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</div>
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</div>
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</div>
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<p>
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The <span class="bold"><strong>pagep</strong></span> parameter references memory
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into which a pointer to the returned page is copied.
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</p>
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</div>
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<div class="sect3" 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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<h4 class="title"><a id="id3917422"></a>pgnoaddr</h4>
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</div>
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</div>
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</div>
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<p>
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If the <span class="bold"><strong>flags</strong></span> parameter is set to
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<code class="literal">DB_MPOOL_LAST</code> or <code class="literal">DB_MPOOL_NEW</code>, the
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page number of the created page is copied into the memory location to
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which the <span class="bold"><strong>pgnoaddr</strong></span> parameter refers.
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Otherwise, the <span class="bold"><strong>pgnoaddr</strong></span> parameter is the
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page to create or retrieve.
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</p>
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<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
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<h3 class="title">Note</h3>
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<p>
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Page numbers begin at 0; that is, the first page in the file is page number 0,
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not page number 1.
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</p>
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</div>
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</div>
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<div class="sect3" 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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<h4 class="title"><a id="id3917254"></a>txnid</h4>
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</div>
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</div>
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</div>
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<p>
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If the operation is part of an application-specified transaction, the
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<span class="bold"><strong>txnid</strong></span> parameter is a transaction
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handle returned from <a class="xref" href="txnbegin.html" title="DB_ENV->txn_begin()">DB_ENV->txn_begin()</a>;
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otherwise NULL. A transaction is required if the file is open for multiversion
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concurrency control by passing
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<a class="link" href="dbopen.html#dbopen_DB_MULTIVERSION">DB_MULTIVERSION</a>
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to
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<a class="xref" href="mempfopen.html" title="DB_MPOOLFILE->open()">DB_MPOOLFILE->open()</a>
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and the DB_MPOOL_DIRTY, DB_MPOOL_CREATE or DB_MPOOL_NEW flags were
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specified. Otherwise it is ignored.
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</p>
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</div>
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</div>
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<div class="sect2" 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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<h3 class="title"><a id="id3917473"></a>Errors</h3>
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</div>
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</div>
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</div>
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<p>
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The <code class="methodname">DB_MPOOLFILE->get()</code> <span>
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<span>
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method may fail and return one of the following non-zero errors:
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</span>
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</span>
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</p>
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<div class="sect3" 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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<h4 class="title"><a id="id3917349"></a>EACCES</h4>
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</div>
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</div>
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</div>
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<p>
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The <code class="literal">DB_MPOOL_DIRTY</code> or
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<code class="literal">DB_MPOOL_EDIT</code> flag was set and the source file was
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not opened for writing.
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</p>
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</div>
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<div class="sect3" 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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<h4 class="title"><a id="id3917383"></a>EAGAIN</h4>
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</div>
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</div>
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</div>
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<p>
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The page reference count has overflowed. (This should never happen
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unless there is a bug in the application.)
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</p>
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</div>
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<div class="sect3" 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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<h4 class="title"><a id="id3917630"></a>EINVAL</h4>
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</div>
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</div>
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</div>
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<p>
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If the <code class="literal">DB_MPOOL_NEW</code> flag was set, and the source
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file was not opened for writing; more than one of
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<code class="literal">DB_MPOOL_CREATE</code>, <code class="literal">DB_MPOOL_LAST</code>,
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|||
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|
and <code class="literal">DB_MPOOL_NEW</code> was set; or if an invalid flag
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value or parameter was specified.
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</p>
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</div>
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<div class="sect3" 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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<h4 class="title"><a id="id3916963"></a>DB_LOCK_DEADLOCK</h4>
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</div>
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</div>
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</div>
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<p>
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For transactions configured with
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<a class="link" href="txnbegin.html#txnbegin_DB_TXN_SNAPSHOT">DB_TXN_SNAPSHOT</a>,
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the page has been modified since the transaction began.
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</p>
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</div>
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<div class="sect3" 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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<h4 class="title"><a id="id3916966"></a>ENOMEM</h4>
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</div>
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</div>
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</div>
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<p>
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The cache is full, and no more pages will fit in the cache.
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</p>
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</div>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
|
|||
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<div>
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|||
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<div>
|
|||
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<h3 class="title"><a id="id3917312"></a>Class</h3>
|
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</div>
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</div>
|
|||
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</div>
|
|||
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<p>
|
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|
|
<a class="link" href="env.html" title="Chapter 5. The DB_ENV Handle">DB_ENV</a>, <a class="link" href="memp.html" title="Chapter 8. The DB_MPOOLFILE Handle">DB_MPOOLFILE</a>
|
|||
|
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</p>
|
|||
|
|
</div>
|
|||
|
|
<div class="sect2" lang="en" xml:lang="en">
|
|||
|
|
<div class="titlepage">
|
|||
|
|
<div>
|
|||
|
|
<div>
|
|||
|
|
<h3 class="title"><a id="id3917669"></a>See Also</h3>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
<p>
|
|||
|
|
<a class="xref" href="memp.html#memplist" title="Memory Pools and Related Methods">Memory Pools 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="mempfclose.html">Prev</a> </td>
|
|||
|
|
<td width="20%" align="center">
|
|||
|
|
<a accesskey="u" href="memp.html">Up</a>
|
|||
|
|
</td>
|
|||
|
|
<td width="40%" align="right"> <a accesskey="n" href="mempfopen.html">Next</a></td>
|
|||
|
|
</tr>
|
|||
|
|
<tr>
|
|||
|
|
<td width="40%" align="left" valign="top">DB_MPOOLFILE->close() </td>
|
|||
|
|
<td width="20%" align="center">
|
|||
|
|
<a accesskey="h" href="index.html">Home</a>
|
|||
|
|
</td>
|
|||
|
|
<td width="40%" align="right" valign="top"> DB_MPOOLFILE->open()</td>
|
|||
|
|
</tr>
|
|||
|
|
</table>
|
|||
|
|
</div>
|
|||
|
|
</body>
|
|||
|
|
</html>
|