125 lines
6.1 KiB
HTML
125 lines
6.1 KiB
HTML
<!--$Id: env_set_cachesize.html 63573 2008-05-23 21:43:21Z trent.nelson $-->
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<!--Copyright (c) 1997,2008 Oracle. All rights reserved.-->
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<!--See the file LICENSE for redistribution information.-->
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<html>
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<head>
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<title>Berkeley DB: DbEnv::set_cachesize</title>
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<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++">
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</head>
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<body bgcolor=white>
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<table width="100%"><tr valign=top>
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<td>
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<b>DbEnv::set_cachesize</b>
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</td>
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<td align=right>
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<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a>
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<a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td>
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</tr></table>
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<hr size=1 noshade>
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<tt>
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<b><pre>
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#include <db_cxx.h>
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<p>
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int
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DbEnv::set_cachesize(u_int32_t gbytes, u_int32_t bytes, int ncache);
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<p>
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int
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DbEnv::get_cachesize(u_int32_t *gbytesp, u_int32_t *bytesp, int *ncachep);
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</pre></b>
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<hr size=1 noshade>
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<b>Description: DbEnv::set_cachesize</b>
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<p>Set the size of the shared memory buffer pool -- that is, the cache.
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The cache should be the size of the normal working data set of the
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application, with some small amount of additional memory for unusual
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situations. (Note: the working set is not the same as the number of
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pages accessed simultaneously, and is usually much larger.)</p>
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<p>The default cache size is 256KB, and may not be specified as less than
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20KB. Any cache size less than 500MB is automatically increased by 25%
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to account for buffer pool overhead; cache sizes larger than 500MB are
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used as specified. The maximum size of a single cache is 4GB on 32-bit
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systems and 10TB on 64-bit systems. (All sizes are in powers-of-two,
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that is, 256KB is 2^18 not 256,000.) For information on tuning the Berkeley DB
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cache size, see <a href="../ref/am_conf/cachesize.html">Selecting a
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cache size</a>.</p>
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<p>It is possible to specify caches to Berkeley DB large enough they cannot be
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allocated contiguously on some architectures. For example, some
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releases of Solaris limit the amount of memory that may be allocated
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contiguously by a process. If <b>ncache</b> is 0 or 1, the cache will
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be allocated contiguously in memory. If it is greater than 1, the cache
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will be split across <b>ncache</b> separate regions, where the
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<b>region size</b> is equal to the initial cache size divided by
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<b>ncache</b>.</p>
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<p>The memory pool may be resized by calling DbEnv::set_cachesize
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after the environment is open. The supplied size will be rounded to
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the nearest multiple of the region size and may not be larger than the
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maximum size configured with <a href="../api_cxx/env_set_cache_max.html">DbEnv::set_cache_max</a>. The
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<b>ncache</b> parameter is ignored when resizing the cache.</p>
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<p>The database environment's initial cache size may also be configured using the
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environment's <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> file. The syntax of the entry in that
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file is a single line with the string "set_cachesize", one or more whitespace
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characters, and the initial cache size specified in three parts: the gigabytes of
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cache, the additional bytes of cache, and the number of caches, also
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separated by whitespace characters. For example, "set_cachesize 2
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524288000 3" would create a 2.5GB logical cache, split between three
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physical caches.
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Because the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> file is read when the database environment
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is opened, it will silently overrule configuration done before that
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time.</p>
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<p>The DbEnv::set_cachesize method configures a database environment, not only operations
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performed using the specified <a href="../api_cxx/env_class.html">DbEnv</a> handle.</p>
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<p>The DbEnv::set_cachesize method may be called at any time during the life of the
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application.</p>
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<p>The DbEnv::set_cachesize method
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either returns a non-zero error value
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or throws an exception that encapsulates a non-zero error value on
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failure, and returns 0 on success.
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</p>
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<b>Parameters</b> <br>
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<b>bytes</b><ul compact><li>The size of the cache is set to <b>gbytes</b> gigabytes plus <b>bytes</b>.</ul>
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<b>gbytes</b><ul compact><li>The size of the cache is set to <b>gbytes</b> gigabytes plus <b>bytes</b>.</ul>
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<b>ncache</b><ul compact><li>The <b>ncache</b> parameter is the number of caches to create.</ul>
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<br>
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<br><b>Errors</b>
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<p>The DbEnv::set_cachesize method
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may fail and throw
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<a href="../api_cxx/except_class.html">DbException</a>,
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encapsulating one of the following non-zero errors, or return one of
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the following non-zero errors:</p>
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<br>
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<b>EINVAL</b><ul compact><li>If the specified cache size was impossibly small;
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; or if an
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invalid flag value or parameter was specified.</ul>
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<br>
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<hr size=1 noshade>
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<b>Description: DbEnv::get_cachesize</b>
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<p>The DbEnv::get_cachesize method returns the current size and composition of the
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cache.</p>
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<p>The DbEnv::get_cachesize method may be called at any time during the life of the
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application.</p>
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<p>The DbEnv::get_cachesize method
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either returns a non-zero error value
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or throws an exception that encapsulates a non-zero error value on
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failure, and returns 0 on success.
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</p>
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<b>Parameters</b> <br>
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<b>bytesp</b><ul compact><li>The <b>bytesp</b> parameter references memory into which
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the additional bytes of memory in the cache is copied.</ul>
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<b>gbytesp</b><ul compact><li>The <b>gbytesp</b> parameter references memory into which
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the gigabytes of memory in the cache is copied.</ul>
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<b>ncachep</b><ul compact><li>The <b>ncachep</b> parameter references memory into which
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the number of caches is copied.</ul>
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<br>
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<hr size=1 noshade>
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<br><b>Class</b>
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<a href="../api_cxx/env_class.html">DbEnv</a>
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<br><b>See Also</b>
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<a href="../api_cxx/env_list.html">Database Environments and Related Methods</a>
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</tt>
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<table width="100%"><tr><td><br></td><td align=right>
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<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>
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</td></tr></table>
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<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font>
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