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<title>Berkeley DB: DB_ENV->set_cachesize</title>
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<h1>DB_ENV->set_cachesize</h1>
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<a href="../api_c/c_index.html"><img src="../images/api.gif" alt="API"></a><a href="../reftoc.html"><img src="../images/ref.gif" alt="Ref"></a>
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DB_ENV->set_cachesize(DB_ENV *dbenv,
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u_int32_t gbytes, u_int32_t bytes, int ncache);
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<p>Set the size of the shared memory buffer pool -- that is, the cache --
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to <b>gbytes</b> gigabytes plus <b>bytes</b>. The cache should be
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the size of the normal working data set of the application, with some
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small amount of additional memory for unusual situations. (Note: the
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working set is not the same as the number of pages accessed
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simultaneously, and should be quite a bit larger!)
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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 current maximum size of a single cache is 4GB.
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For information on tuning the Berkeley DB cache size, see
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<a href="../ref/am_conf/cachesize.html">Selecting a cache size</a>.
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<p>It is possible to specify caches to Berkeley DB that are large enough so that
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they cannot be allocated contiguously on some architectures. For
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example, some releases of Solaris limit the amount of memory that may
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be allocated contiguously by a process. If <b>ncache</b> is 0 or 1,
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the cache will be allocated contiguously in memory. If it is greater
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than 1, the cache will be broken up into <b>ncache</b> equally sized,
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separate pieces of memory.
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<p>Because databases opened within Berkeley DB environments use the cache
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specified to the environment, it is an error to attempt to set a
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cache in a database created within an environment.
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<p>The DB_ENV->set_cachesize interface may be used only to configure Berkeley DB before
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the <a href="../api_c/env_open.html">DB_ENV->open</a> interface is called.
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<p>The DB_ENV->set_cachesize function returns a non-zero error value on failure and 0 on success.
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<p>The database environment's cache size may also be set using the environment's
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<b>DB_CONFIG</b> file. The syntax of the entry in that file is a
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single line with the string "set_cachesize", one or more whitespace characters,
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and the three arguments specified to this interface, separated by whitespace
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characters, for example, "set_cachesize 1 500 2". Because the <b>DB_CONFIG</b> file is read when the database
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environment is opened, it will silently overrule configuration done
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<p>The DB_ENV->set_cachesize function may fail and return a non-zero error for the following conditions:
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<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
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<a href="../api_c/env_open.html">DB_ENV->open</a>
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<p>The specified cache size was impossibly small.
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<p>The DB_ENV->set_cachesize function may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions.
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If a catastrophic error has occurred, the DB_ENV->set_cachesize function may fail and return
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<a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a>, in which case all subsequent Berkeley DB calls will fail
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<a href="../api_c/env_create.html">db_env_create</a>,
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<a href="../api_c/env_close.html">DB_ENV->close</a>,
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<a href="../api_c/env_err.html">DB_ENV->err</a>, <a href="../api_c/env_err.html">DB_ENV->errx</a>
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<a href="../api_c/env_open.html">DB_ENV->open</a>,
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<a href="../api_c/env_remove.html">DB_ENV->remove</a>,
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<a href="../api_c/env_set_alloc.html">DB_ENV->set_alloc</a>,
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<a href="../api_c/env_set_cachesize.html">DB_ENV->set_cachesize</a>,
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<a href="../api_c/env_set_data_dir.html">DB_ENV->set_data_dir</a>,
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<a href="../api_c/env_set_errcall.html">DB_ENV->set_errcall</a>,
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<a href="../api_c/env_set_errfile.html">DB_ENV->set_errfile</a>,
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<a href="../api_c/env_set_errpfx.html">DB_ENV->set_errpfx</a>,
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<a href="../api_c/env_set_feedback.html">DB_ENV->set_feedback</a>,
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<a href="../api_c/env_set_flags.html">DB_ENV->set_flags</a>,
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<a href="../api_c/env_set_mutexlocks.html">DB_ENV->set_mutexlocks</a>,
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<a href="../api_c/env_set_pageyield.html">db_env_set_pageyield</a>,
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<a href="../api_c/env_set_paniccall.html">DB_ENV->set_paniccall</a>,
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<a href="../api_c/env_set_panicstate.html">db_env_set_panicstate</a>,
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<a href="../api_c/env_set_rec_init.html">DB_ENV->set_recovery_init</a>,
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<a href="../api_c/env_set_rpc_server.html">DB_ENV->set_rpc_server</a>,
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<a href="../api_c/env_set_region_init.html">db_env_set_region_init</a>,
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<a href="../api_c/env_set_shm_key.html">DB_ENV->set_shm_key</a>,
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<a href="../api_c/env_set_tas_spins.html">db_env_set_tas_spins</a>,
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<a href="../api_c/env_set_tmp_dir.html">DB_ENV->set_tmp_dir</a>,
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<a href="../api_c/env_set_verbose.html">DB_ENV->set_verbose</a>,
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<a href="../api_c/env_strerror.html">db_strerror</a>
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<a href="../api_c/env_version.html">db_version</a>.
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