99 lines
4.4 KiB
HTML
99 lines
4.4 KiB
HTML
<!--$Id: env_set_mp_mmapsize.html 63573 2008-05-23 21:43:21Z trent.nelson $-->
|
|
<!--Copyright (c) 1997,2008 Oracle. All rights reserved.-->
|
|
<!--See the file LICENSE for redistribution information.-->
|
|
<html>
|
|
<head>
|
|
<title>Berkeley DB: DbEnv::set_mp_mmapsize</title>
|
|
<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
|
|
<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++">
|
|
</head>
|
|
<body bgcolor=white>
|
|
<table width="100%"><tr valign=top>
|
|
<td>
|
|
<b>DbEnv::set_mp_mmapsize</b>
|
|
</td>
|
|
<td align=right>
|
|
<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a>
|
|
<a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td>
|
|
</tr></table>
|
|
<hr size=1 noshade>
|
|
<tt>
|
|
<b><pre>
|
|
#include <db_cxx.h>
|
|
<p>
|
|
int
|
|
DbEnv::set_mp_mmapsize(size_t mp_mmapsize);
|
|
<p>
|
|
int
|
|
DbEnv::get_mp_mmapsize(size_t *mp_mmapsizep);
|
|
</pre></b>
|
|
<hr size=1 noshade>
|
|
<b>Description: DbEnv::set_mp_mmapsize</b>
|
|
<p>Files that are opened read-only in the pool (and that satisfy a few
|
|
other criteria) are, by default, mapped into the process address space
|
|
instead of being copied into the local cache. This can result in
|
|
better-than-usual performance because available virtual memory is
|
|
normally much larger than the local cache, and page faults are faster
|
|
than page copying on many systems. However, it can cause resource
|
|
starvation in the presence of limited virtual memory, and it can result
|
|
in immense process sizes in the presence of large databases.</p>
|
|
<p>The DbEnv::get_mp_mmapsize method sets the maximum file size, in bytes,
|
|
for a file to be mapped into the process address space. If no value is
|
|
specified, it defaults to 10MB.</p>
|
|
<p>The database environment's maximum mapped file size may also be configured using the
|
|
environment's <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> file. The syntax of the entry in that
|
|
file is a single line with the string "set_mp_mmapsize", one or more whitespace
|
|
characters, and the size in bytes.
|
|
Because the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> file is read when the database environment
|
|
is opened, it will silently overrule configuration done before that
|
|
time.</p>
|
|
<p>The DbEnv::set_mp_mmapsize method configures a database environment, not only operations
|
|
performed using the specified <a href="../api_cxx/env_class.html">DbEnv</a> handle.</p>
|
|
<p>The DbEnv::set_mp_mmapsize method may be called at any time during the life of the
|
|
application.</p>
|
|
<p>The DbEnv::set_mp_mmapsize method
|
|
either returns a non-zero error value
|
|
or throws an exception that encapsulates a non-zero error value on
|
|
failure, and returns 0 on success.
|
|
</p>
|
|
<b>Parameters</b> <br>
|
|
<b>mp_mmapsize</b><ul compact><li>The <b>mp_mmapsize</b> parameter is the maximum file size, in bytes,
|
|
for a file to be mapped into the process address space.</ul>
|
|
<br>
|
|
<br><b>Errors</b>
|
|
<p>The DbEnv::set_mp_mmapsize method
|
|
may fail and throw
|
|
<a href="../api_cxx/except_class.html">DbException</a>,
|
|
encapsulating one of the following non-zero errors, or return one of
|
|
the following non-zero errors:</p>
|
|
<br>
|
|
<b>EINVAL</b><ul compact><li>If the method was called after <a href="../api_cxx/env_open.html">DbEnv::open</a> was called; or if an
|
|
invalid flag value or parameter was specified.</ul>
|
|
<br>
|
|
<hr size=1 noshade>
|
|
<b>Description: DbEnv::get_mp_mmapsize</b>
|
|
<p>The DbEnv::get_mp_mmapsize method returns the maximum file map size.</p>
|
|
<p>The DbEnv::get_mp_mmapsize method may be called at any time during the life of the
|
|
application.</p>
|
|
<p>The DbEnv::get_mp_mmapsize method
|
|
either returns a non-zero error value
|
|
or throws an exception that encapsulates a non-zero error value on
|
|
failure, and returns 0 on success.
|
|
</p>
|
|
<b>Parameters</b> <br>
|
|
<b>mp_mmapsizep</b><ul compact><li>The DbEnv::get_mp_mmapsize method returns the
|
|
maximum file map size in <b>mp_mmapsizep</b>.</ul>
|
|
<br>
|
|
<hr size=1 noshade>
|
|
<br><b>Class</b>
|
|
<a href="../api_cxx/env_class.html">DbEnv</a>, <a href="../api_cxx/mempfile_class.html">DbMpoolFile</a>
|
|
<br><b>See Also</b>
|
|
<a href="../api_cxx/memp_list.html">Memory Pools and Related Methods</a>
|
|
</tt>
|
|
<table width="100%"><tr><td><br></td><td align=right>
|
|
<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a>
|
|
</td></tr></table>
|
|
<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font>
|
|
</body>
|
|
</html>
|