<?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_MPOOLFILE->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="memp.html" title="Chapter 8. The DB_MPOOLFILE Handle" /> <link rel="prev" href="mempfclose.html" title="DB_MPOOLFILE->close()" /> <link rel="next" href="mempfopen.html" title="DB_MPOOLFILE->open()" /> </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_MPOOLFILE->get()</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="mempfclose.html">Prev</a> </td> <th width="60%" align="center">Chapter 8. The DB_MPOOLFILE Handle </th> <td width="20%" align="right"> <a accesskey="n" href="mempfopen.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="mempfget"></a>DB_MPOOLFILE->get()</h2> </div> </div> </div> <pre class="programlisting">#include <db.h> int DB_MPOOLFILE->get(DB_MPOOLFILE *mpf, db_pgno_t *pgnoaddr, DB_TXN * txnid, u_int32_t flags, void **pagep); </pre> <p> The <code class="methodname">DB_MPOOLFILE->get()</code> method returns pages from the cache. </p> <p> All pages returned by <code class="methodname">DB_MPOOLFILE->get()</code> will be retained (that is, <span class="emphasis"><em>latched</em></span>) in the cache until a subsequent call to <a class="xref" href="mempput.html" title="DB_MPOOLFILE->put()">DB_MPOOLFILE->put()</a>. There is no deadlock detection among latches so care must be taken in the application if the DB_MPOOL_DIRTY or DB_MPOOL_EDIT flags are used as these get exlusive latches on the pages. </p> <p> The returned page is <span class="bold"><strong>size_t</strong></span> type aligned. </p> <p> Fully or partially created pages have all their bytes set to a nul byte, unless the <a class="xref" href="mempset_clear_len.html" title="DB_MPOOLFILE->set_clear_len()">DB_MPOOLFILE->set_clear_len()</a> method was called to specify other behavior before the file was opened. </p> <p><a id="fget_DB_PAGE_NOTFOUND"></a> The <code class="methodname">DB_MPOOLFILE->get()</code> method will return <code class="literal">DB_PAGE_NOTFOUND</code> if the requested page does not exist and DB_MPOOL_CREATE was not set. Unless otherwise specified, the <code class="methodname">DB_MPOOLFILE->get()</code> <span> <span> method returns a non-zero error value on failure and 0 on success. </span> </span> </p> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp61387872"></a>Parameters</h3> </div> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp61387224"></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="mpoolfget_DB_MPOOL_CREATE"></a> <code class="literal">DB_MPOOL_CREATE</code> </p> <p> If the specified page does not exist, create it. In this case, the <a class="link" href="mempregister.html" title="DB_ENV->memp_register()">pgin</a> method, if specified, is called. </p> </li> <li> <p><a id="fget_DB_MPOOL_DIRTY"></a> <code class="literal">DB_MPOOL_DIRTY</code> </p> <p> The page will be modified and must be written to the source file before being evicted from the cache. For files open with the <a class="link" href="dbopen.html#dbopen_DB_MULTIVERSION">DB_MULTIVERSION</a> flag set, a new copy of the page will be made if this is the first time the specified transaction is modifying it. A page fetched with the <code class="literal">DB_MPOOL_DIRTY</code> flag will be <span class="bold"><strong>exclusively latched</strong></span> until a subsequent call to <a class="xref" href="mempput.html" title="DB_MPOOLFILE->put()">DB_MPOOLFILE->put()</a>. </p> </li> <li> <p><a id="fget_DB_MPOOL_EDIT"></a> <code class="literal">DB_MPOOL_EDIT</code> </p> <p> The page will be modified and must be written to the source file before being evicted from the cache. No copy of the page will be made, regardless of the <a class="link" href="dbopen.html#dbopen_DB_MULTIVERSION">DB_MULTIVERSION</a> setting. This flag is only intended for use in situations where a transaction handle is not available, such as during aborts or recovery. A page fetched with the <code class="literal">DB_MPOOL_EDIT</code> flag will be <span class="bold"><strong>exclusively latched</strong></span> until a subsequent call to <a class="xref" href="mempput.html" title="DB_MPOOLFILE->put()">DB_MPOOLFILE->put()</a>. </p> </li> <li> <p><a id="fget_DB_MPOOL_LAST"></a> <code class="literal">DB_MPOOL_LAST</code> </p> <p> Return the last page of the source file, and copy its page number into the memory location to which <span class="bold"><strong>pgnoaddr</strong></span> refers. </p> </li> <li> <p><a id="mpoolfget_DB_MPOOL_NEW"></a> <code class="literal">DB_MPOOL_NEW</code> </p> <p> Create a new page in the file, and copy its page number into the memory location to which <span class="bold"><strong>pgnoaddr</strong></span> refers. In this case, the <code class="literal">pgin_fcn</code> callback, if specified on <a class="xref" href="mempregister.html" title="DB_ENV->memp_register()">DB_ENV->memp_register()</a>, is <span class="bold"><strong>not</strong></span> called. </p> </li> </ul> </div> <p> The <code class="literal">DB_MPOOL_CREATE</code>, <code class="literal">DB_MPOOL_LAST</code>, and <code class="literal">DB_MPOOL_NEW</code> flags are mutually exclusive. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp61393160"></a>pagep</h4> </div> </div> </div> <p> The <span class="bold"><strong>pagep</strong></span> parameter references memory into which a pointer to the returned page is copied. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp61402880"></a>pgnoaddr</h4> </div> </div> </div> <p> If the <span class="bold"><strong>flags</strong></span> parameter is set to <code class="literal">DB_MPOOL_LAST</code> or <code class="literal">DB_MPOOL_NEW</code>, the page number of the created page is copied into the memory location to which the <span class="bold"><strong>pgnoaddr</strong></span> parameter refers. Otherwise, the <span class="bold"><strong>pgnoaddr</strong></span> parameter is the page to create or retrieve. </p> <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"> <h3 class="title">Note</h3> <p> Page numbers begin at 0; that is, the first page in the file is page number 0, not page number 1. </p> </div> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp61404856"></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>; otherwise NULL. A transaction is required if the file is open for multiversion concurrency control by passing <a class="link" href="dbopen.html#dbopen_DB_MULTIVERSION">DB_MULTIVERSION</a> to <a class="xref" href="mempfopen.html" title="DB_MPOOLFILE->open()">DB_MPOOLFILE->open()</a> and the DB_MPOOL_DIRTY, DB_MPOOL_CREATE or DB_MPOOL_NEW flags were specified. Otherwise it is ignored. </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp61405936"></a>Errors</h3> </div> </div> </div> <p> The <code class="methodname">DB_MPOOLFILE->get()</code> <span> <span> method may fail and 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="idp61398608"></a>EACCES</h4> </div> </div> </div> <p> The <code class="literal">DB_MPOOL_DIRTY</code> or <code class="literal">DB_MPOOL_EDIT</code> flag was set and the source file was not opened for writing. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp61400504"></a>EAGAIN</h4> </div> </div> </div> <p> The page reference count has overflowed. (This should never happen unless there is a bug in the application.) </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp61415336"></a>EINVAL</h4> </div> </div> </div> <p> If the <code class="literal">DB_MPOOL_NEW</code> flag was set, and the source file was not opened for writing; more than one of <code class="literal">DB_MPOOL_CREATE</code>, <code class="literal">DB_MPOOL_LAST</code>, and <code class="literal">DB_MPOOL_NEW</code> was set; or if an invalid flag value or parameter was specified. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp61368272"></a>DB_LOCK_DEADLOCK</h4> </div> </div> </div> <p> For transactions configured with <a class="link" href="txnbegin.html#txnbegin_DB_TXN_SNAPSHOT">DB_TXN_SNAPSHOT</a>, the page has been modified since the transaction began. </p> </div> <div class="sect3" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h4 class="title"><a id="idp61397872"></a>ENOMEM</h4> </div> </div> </div> <p> The cache is full, and no more pages will fit in the cache. </p> </div> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp61396256"></a>Class</h3> </div> </div> </div> <p> <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> </p> </div> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="idp61417672"></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>