<!--$Id: env_set_mp_mmapsize.so,v 10.40 2004/09/28 15:04:21 bostic Exp $--> <!--Copyright (c) 1997,2007 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> <h3>DbEnv::set_mp_mmapsize</h3> </td> <td align=right> <a href="../../db46-devel-4.6.21/api_cxx/api_core.html"><img src="../../db46-devel-4.6.21/images/api.gif" alt="API"></a> <a href="../../db46-devel-4.6.21/ref/toc.html"><img src="../../db46-devel-4.6.21/images/ref.gif" alt="Ref"></a></td> </tr></table> <hr size=1 noshade> <tt> <h3><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></h3> <hr size=1 noshade> <h3>Description: DbEnv::set_mp_mmapsize</h3> <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 <b>DB_CONFIG</b> 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 <b>DB_CONFIG</b> 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="../../db46-devel-4.6.21/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> <h3>Parameters</h3> <dl compact> <dt><b>mp_mmapsize</b><dd>The <b>mp_mmapsize</b> parameter is the maximum file size, in bytes, for a file to be mapped into the process address space. </dl> <h3>Errors</h3> <p>The DbEnv::set_mp_mmapsize method may fail and throw <a href="../../db46-devel-4.6.21/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> <dl compact> <dt>EINVAL<dd>If the method was called after <a href="../../db46-devel-4.6.21/api_cxx/env_open.html">DbEnv::open</a> was called; or if an invalid flag value or parameter was specified. </dl> <hr size=1 noshade> <h3>Description: DbEnv::get_mp_mmapsize</h3> <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> <h3>Parameters</h3> <dl compact> <dt><b>mp_mmapsizep</b><dd>The DbEnv::get_mp_mmapsize method returns the maximum file map size in <b>mp_mmapsizep</b>. </dl> <hr size=1 noshade> <h3>Class</h3> <a href="../../db46-devel-4.6.21/api_cxx/env_class.html">DbEnv</a>, <a href="../../db46-devel-4.6.21/api_cxx/mempfile_class.html">DbMpoolFile</a> <h3>See Also</h3> <a href="../../db46-devel-4.6.21/api_cxx/memp_list.html">Memory Pools and Related Methods</a> </tt> <table width="100%"><tr><td><br></td><td align=right> <a href="../../db46-devel-4.6.21/api_cxx/api_core.html"><img src="../../db46-devel-4.6.21/images/api.gif" alt="API"></a><a href="../../db46-devel-4.6.21/ref/toc.html"><img src="../../db46-devel-4.6.21/images/ref.gif" alt="Ref"></a> </td></tr></table> <p><font size=1>Copyright (c) 1996,2007 Oracle. All rights reserved.</font> </body> </html>