1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
|
<!--$Id: intro.html,v 1.1.1.1 2003/11/20 22:14:14 toshok Exp $-->
<!--Copyright 1997-2002 by Sleepycat Software, Inc.-->
<!--All rights reserved.-->
<!--See the file LICENSE for redistribution information.-->
<html>
<head>
<title>Berkeley DB Reference Guide: Berkeley DB and the memory pool</title>
<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
<meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,java,C,C++">
</head>
<body bgcolor=white>
<a name="2"><!--meow--></a><a name="3"><!--meow--></a><a name="4"><!--meow--></a>
<table width="100%"><tr valign=top>
<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Memory Pool Subsystem</dl></h3></td>
<td align=right><a href="../../ref/log/limits.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../../reftoc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../../ref/mp/config.html"><img src="../../images/next.gif" alt="Next"></a>
</td></tr></table>
<p>
<h1 align=center>Berkeley DB and the memory pool</h1>
<p>The Memory Pool subsystem is the general-purpose shared memory buffer
pool used by Berkeley DB. This module is useful outside of the Berkeley DB package
for processes that require page-oriented, shared and cached file access.
<p>A <i>memory pool</i> is a memory cache shared among any number of
threads of control. The <a href="../../api_c/env_open.html#DB_INIT_MPOOL">DB_INIT_MPOOL</a> flag to the
<a href="../../api_c/env_open.html">DB_ENV->open</a> method opens and optionally creates a memory pool. When
that pool is no longer in use, it should be closed using the
<a href="../../api_c/env_close.html">DB_ENV->close</a> method.
<p>The <a href="../../api_c/memp_fcreate.html">DB_ENV->memp_fcreate</a> method returns a <a href="../../api_c/mempfile_class.html">DB_MPOOLFILE</a> handle on an
underlying file within the memory pool. The file may be opened using
the <a href="../../api_c/memp_fopen.html">DB_MPOOLFILE->open</a> method. The <a href="../../api_c/memp_fget.html">DB_MPOOLFILE->get</a> method is used to retrieve
pages from files in the pool. All retrieved pages must be subsequently
returned using the <a href="../../api_c/memp_fput.html">DB_MPOOLFILE->put</a> method. At the time pages are returned,
they may be marked <b>dirty</b>, which causes them to be written to
the underlying file before being discarded from the pool. If there is
insufficient room to bring a new page in the pool, a page is selected
to be discarded from the pool using a least-recently-used algorithm.
Pages in files may also be explicitly marked clean or dirty using the
<a href="../../api_c/memp_fset.html">DB_MPOOLFILE->set</a> method. All dirty pages in the pool from the file may be
flushed using the <a href="../../api_c/memp_fsync.html">DB_MPOOLFILE->sync</a> method. When the file handle is no
longer in use, it should be closed using the <a href="../../api_c/memp_fclose.html">DB_MPOOLFILE->close</a> method.
<p>There are additional configuration interfaces that apply when opening
a new file in the memory pool:
<p><ul type=disc>
<li>The <a href="../../api_c/memp_set_clear_len.html">DB_MPOOLFILE->set_clear_len</a> method specifies the number of bytes to clear
when creating a new page in the memory pool.
<li>The <a href="../../api_c/memp_set_fileid.html">DB_MPOOLFILE->set_fileid</a> method specifies a unique ID associated with the file.
<li>The <a href="../../api_c/memp_set_ftype.html">DB_MPOOLFILE->set_ftype</a> method specifies the type of file for the purposes of
page input and output processing.
<li>The <a href="../../api_c/memp_set_lsn_offset.html">DB_MPOOLFILE->set_lsn_offset</a> method specifies the byte offset of each page's
log sequence number (<a href="../../api_c/lsn_class.html">DB_LSN</a>) for the purposes of transaction
checkpoints.
<li>The <a href="../../api_c/memp_set_pgcookie.html">DB_MPOOLFILE->set_pgcookie</a> method specifies an application provided argument
for the purposes of page input and output processing.
</ul>
<p>There are additional interfaces for the memory pool as a whole:
<p><ul type=disc>
<li>It is possible to gradually flush buffers from the pool in order to
maintain a consistent percentage of clean buffers in the pool using
the <a href="../../api_c/memp_trickle.html">DB_ENV->memp_trickle</a> method.
<li>Because special-purpose processing may be necessary when pages are read
or written (for example, compression or endian conversion), the
<a href="../../api_c/memp_register.html">DB_ENV->memp_register</a> function allows applications to specify automatic
input and output processing in these cases.
<li>The <a href="../../utility/db_stat.html">db_stat</a> utility uses the <a href="../../api_c/memp_stat.html">DB_ENV->memp_stat</a> method to display
statistics about the efficiency of the pool.
<li>All dirty pages in the pool may be flushed using the <a href="../../api_c/memp_sync.html">DB_ENV->memp_sync</a> method.
In addition, <a href="../../api_c/memp_sync.html">DB_ENV->memp_sync</a> takes an argument that is specific to
database systems, and which allows the memory pool to be flushed up to
a specified log sequence number (<a href="../../api_c/lsn_class.html">DB_LSN</a>).
<li>The entire pool may be discarded using the <a href="../../api_c/env_remove.html">DB_ENV->remove</a> method.
</ul>
<!--$Id: intro.html,v 1.1.1.1 2003/11/20 22:14:14 toshok Exp $-->
<p><table border=1 align=center>
<tr><th>Memory Pools and Related Methods</th><th>Description</th></tr>
<tr><td><a href="../../api_c/env_set_cachesize.html">DB_ENV->set_cachesize</a></td><td>Set the environment cache size</td></tr>
<tr><td><a href="../../api_c/env_set_mp_mmapsize.html">DB_ENV->set_mp_mmapsize</a></td><td>Set maximum mapped-in database file size</td></tr>
<tr><td><a href="../../api_c/memp_register.html">DB_ENV->memp_register</a></td><td>Register input/output functions for a file in a memory pool</td></tr>
<tr><td><a href="../../api_c/memp_stat.html">DB_ENV->memp_stat</a></td><td>Return memory pool statistics</td></tr>
<tr><td><a href="../../api_c/memp_sync.html">DB_ENV->memp_sync</a></td><td>Flush pages from a memory pool</td></tr>
<tr><td><a href="../../api_c/memp_trickle.html">DB_ENV->memp_trickle</a></td><td>Trickle flush pages from a memory pool</td></tr>
<tr><td><a href="../../api_c/memp_fcreate.html">DB_ENV->memp_fcreate</a></td><td>Open a file in a memory pool</td></tr>
<tr><td><a href="../../api_c/memp_fclose.html">DB_MPOOLFILE->close</a></td><td>Close a file in a memory pool</td></tr>
<tr><td><a href="../../api_c/memp_fget.html">DB_MPOOLFILE->get</a></td><td>Get page from a file in a memory pool</td></tr>
<tr><td><a href="../../api_c/memp_fopen.html">DB_MPOOLFILE->open</a></td><td>Open a file in a memory pool</td></tr>
<tr><td><a href="../../api_c/memp_fput.html">DB_MPOOLFILE->put</a></td><td>Return a page to a memory pool</td></tr>
<tr><td><a href="../../api_c/memp_fset.html">DB_MPOOLFILE->set</a></td><td>Set memory pool page status</td></tr>
<tr><td><a href="../../api_c/memp_fsync.html">DB_MPOOLFILE->sync</a></td><td>Flush pages from a file in a memory pool</td></tr>
<tr><td><a href="../../api_c/memp_set_clear_len.html">DB_MPOOLFILE->set_clear_len</a></td><td>Set file page bytes to be cleared</td></tr>
<tr><td><a href="../../api_c/memp_set_fileid.html">DB_MPOOLFILE->set_fileid</a></td><td>Set file unique identifier</td></tr>
<tr><td><a href="../../api_c/memp_set_ftype.html">DB_MPOOLFILE->set_ftype</a></td><td>Set file type</td></tr>
<tr><td><a href="../../api_c/memp_set_lsn_offset.html">DB_MPOOLFILE->set_lsn_offset</a></td><td>Set file log-sequence-number offset</td></tr>
<tr><td><a href="../../api_c/memp_set_pgcookie.html">DB_MPOOLFILE->set_pgcookie</a></td><td>Set file cookie for pgin/pgout</td></tr>
</table>
<table width="100%"><tr><td><br></td><td align=right><a href="../../ref/log/limits.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../../reftoc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../../ref/mp/config.html"><img src="../../images/next.gif" alt="Next"></a>
</td></tr></table>
<p><font size=1><a href="http://www.sleepycat.com">Copyright Sleepycat Software</a></font>
</body>
</html>
|
