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<h1>DbMpoolFile</h1>
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<h3><pre>
#include <db_cxx.h>
<p>
class DbMpoolFile {
public:
DB_MPOOLFILE *DbMpoolFile::get_DB_MPOOLFILE();
const DB_MPOOLFILE *DbMpoolFile::get_const_DB_MPOOLFILE() const;
...
};
</pre></h3>
<h1>Description</h1>
<p>The memory pool interfaces for the Berkeley DB database environment are
methods of the <a href="../api_cxx/env_class.html">DbEnv</a> handle. The <a href="../api_cxx/env_class.html">DbEnv</a> memory pool
methods and the DbMpoolFile class provide general-purpose,
page-oriented buffer management of files. Although designed to work
with the other <a href="../api_cxx/db_class.html">Db</a> classes, they are also useful for more general
purposes. The memory pools are referred to in this document as simply
<i>pools</i>.
<p>Pools may be shared between processes. Pools are usually filled by
pages from one or more files. Pages in the pool are replaced in LRU
(least-recently-used) order, with each new page replacing the page that
has been unused the longest. Pages retrieved from the pool using
<a href="../api_cxx/memp_fget.html">DbMpoolFile::get</a> are <i>pinned</i> in the pool until they are
returned to the control of the buffer pool using the <a href="../api_cxx/memp_fput.html">DbMpoolFile::put</a>
method.
<p>The DbMpoolFile object is the handle for a file in the memory
pool. The handle is not free-threaded. Once the <a href="../api_cxx/memp_fclose.html">DbMpoolFile::close</a> method
is called, the handle may not be accessed again, regardless of that
method's return.
<p>Each DbMpoolFile object has an associated DB_MPOOLFILE
structure, which is used by the underlying implementation of Berkeley DB and
its C-language API. The DbMpoolFile::get_DB_MPOOLFILE method returns
a pointer to this struct. Given a const DbMpoolFile object,
DbTxn::get_const_DB_MPOOLFILE returns a const pointer to the same
struct.
<p>These methods may be useful for Berkeley DB applications including both C
and C++ language software. It should not be necessary to use these
calls in a purely C++ application.
<h1>Class</h1>
<a href="../api_cxx/env_class.html">DbEnv</a>, DbMpoolFile
<h1>See Also</h1>
<a href="../api_cxx/memp_list.html">Memory Pools and Related Methods</a>
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