<!--$Id: env_set_cachesize.so,v 10.46 2003/11/08 19:17:28 bostic Exp $--> <!--Copyright 1997-2003 by Sleepycat Software, Inc.--> <!--All rights reserved.--> <!--See the file LICENSE for redistribution information.--> <html> <head> <title>Berkeley DB: DbEnv::set_cachesize</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> <table width="100%"><tr valign=top> <td> <h3>DbEnv::set_cachesize</h3> </td> <td align=right> <a href="../../db42-devel-4.2.52/api_cxx/api_index.html"><img src="../../db42-4.2.52/images/api.gif" alt="API"></a> <a href="../../db42-devel-4.2.52/ref/toc.html"><img src="../../db42-4.2.52/images/ref.gif" alt="Ref"></a> </td></tr></table> <hr size=1 noshade> <tt> <h3><pre> #include <db_cxx.h> <p> int DbEnv::set_cachesize(u_int32_t gbytes, u_int32_t bytes, int ncache); <p> int DbEnv::get_cachesize(u_int32_t *gbytesp, u_int32_t *bytesp, int *ncachep); </pre></h3> <hr size=1 noshade> <h3>Description: DbEnv::set_cachesize</h3> <a name="3"><!--meow--></a> <a name="4"><!--meow--></a> <p>Set the size of the shared memory buffer pool -- that is, the cache. The cache should be the size of the normal working data set of the application, with some small amount of additional memory for unusual situations. (Note: the working set is not the same as the number of pages accessed simultaneously, and is usually much larger.)</p> <p>The default cache size is 256KB, and may not be specified as less than 20KB. Any cache size less than 500MB is automatically increased by 25% to account for buffer pool overhead; cache sizes larger than 500MB are used as specified. The current maximum size of a single cache is 4GB. (All sizes are in powers-of-two, that is, 256KB is 2^32 not 256,000.) For information on tuning the Berkeley DB cache size, see <a href="../../db42-devel-4.2.52/ref/am_conf/cachesize.html">Selecting a cache size</a>.</p> <p>It is possible to specify caches to Berkeley DB larger than 4GB and/or large enough they cannot be allocated contiguously on some architectures. For example, some releases of Solaris limit the amount of memory that may be allocated contiguously by a process. If <b>ncache</b> is 0 or 1, the cache will be allocated contiguously in memory. If it is greater than 1, the cache will be broken up into <b>ncache</b> equally sized, separate pieces of memory.</p> <p>The database environment's cache size may also be set 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_cachesize", one or more whitespace characters, and the cache size specified in three parts: the gigabytes of cache, the additional bytes of cache, and the number of caches, also separated by whitespace characters. For example, "set_cachesize 2 524288000 3" would create a 2.5GB logical cache, split between three physical caches. 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_cachesize method configures a database environment, not only operations performed using the specified <a href="../../db42-devel-4.2.52/api_cxx/env_class.html">DbEnv</a> handle.</p> <p>The DbEnv::set_cachesize method may not be called after the <a href="../../db42-devel-4.2.52/api_cxx/env_open.html">DbEnv::open</a> method is called. If the database environment already exists when <a href="../../db42-devel-4.2.52/api_cxx/env_open.html">DbEnv::open</a> is called, the information specified to DbEnv::set_cachesize will be ignored. </p> <p>The DbEnv::set_cachesize 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> <p><dl compact> <p><dt><b>bytes</b><dd> The size of the cache is set to <b>gbytes</b> gigabytes plus <b>bytes</b>. <p><dt><b>gbytes</b><dd> The size of the cache is set to <b>gbytes</b> gigabytes plus <b>bytes</b>. <p><dt><b>ncache</b><dd> The <b>ncache</b> parameter is the number of caches to create. </dl> <h3>Errors</h3> <p>The DbEnv::set_cachesize method may fail and throw <a href="../../db42-devel-4.2.52/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> <p><dl compact> <p><dt>EINVAL<dd>If the specified cache size was impossibly small; the method was called after <a href="../../db42-devel-4.2.52/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_cachesize</h3> <p>The DbEnv::get_cachesize method returns the current size and composition of the cache.</p> <p>The DbEnv::get_cachesize method may be called at any time during the life of the application.</p> <p>The DbEnv::get_cachesize 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> <p><dl compact> <p><dt><b>bytesp</b><dd> The <b>bytesp</b> parameter references memory into which the additional bytes of memory in the cache is copied. <p><dt><b>gbytesp</b><dd> The <b>gbytesp</b> parameter references memory into which the gigabytes of memory in the cache is copied. <p><dt><b>ncachep</b><dd> The <b>ncachep</b> parameter references memory into which the number of caches is copied. </dl> <hr size=1 noshade> <h3>Class</h3> <a href="../../db42-devel-4.2.52/api_cxx/env_class.html">DbEnv</a> <h3>See Also</h3> <a href="../../db42-devel-4.2.52/api_cxx/env_list.html">Database Environments and Related Methods</a> </tt> <table width="100%"><tr><td><br></td><td align=right> <a href="../../db42-devel-4.2.52/api_cxx/api_index.html"><img src="../../db42-4.2.52/images/api.gif" alt="API"></a><a href="../../db42-devel-4.2.52/ref/toc.html"><img src="../../db42-4.2.52/images/ref.gif" alt="Ref"></a> </td></tr></table> <p><font size=1><a href="../../db42-devel-4.2.52/sleepycat/legal.html">Copyright (c) 1996-2003</a> <a href="http://www.sleepycat.com">Sleepycat Software, Inc.</a> - All rights reserved.</font> </body> </html>
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