Import BSDDB 4.7.25 (as of svn r89086)
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Zachary Ware
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docs/api_cxx/env_set_tx_max.html
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docs/api_cxx/env_set_tx_max.html
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<!--$Id: env_set_tx_max.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_tx_max</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_tx_max</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_tx_max(u_int32_t max);
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<p>
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int
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DbEnv::get_tx_max(u_int32_t *tx_maxp);
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</pre></b>
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<hr size=1 noshade>
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<b>Description: DbEnv::set_tx_max</b>
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<p>Configure the Berkeley DB database environment to support at least <b>max</b>
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active transactions. This value bounds the size of the memory allocated
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for transactions. Child transactions are counted as active until they
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either commit or abort.</p>
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<p>Transactions that update multiversion databases are not freed until the
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last page version that the transaction created is flushed from cache.
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This means that applications using multi-version concurrency control may
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need a transaction for each page in cache, in the extreme case.</p>
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<p>When all of the memory available in the database environment for
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transactions is in use, calls to <a href="../api_cxx/txn_begin.html">DbEnv::txn_begin</a> will fail (until some
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active transactions complete). If this interface is never called, the
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database environment is configured to support at least 100 active
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transactions.</p>
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<p>The database environment's number of active transactions 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_tx_max", one or more whitespace
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characters, and the number of transactions.
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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_tx_max 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_tx_max method may not be called after the <a href="../api_cxx/env_open.html">DbEnv::open</a> method is
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called.
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If the database environment already exists when
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<a href="../api_cxx/env_open.html">DbEnv::open</a> is called, the information specified to DbEnv::set_tx_max
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will be ignored.
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</p>
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<p>The DbEnv::set_tx_max 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>max</b><ul compact><li>The <b>max</b> parameter configures the minimum number of
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simultaneously active transactions supported by Berkeley DB database
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environment.</ul>
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<br>
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<br><b>Errors</b>
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<p>The DbEnv::set_tx_max 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 method was called after <a href="../api_cxx/env_open.html">DbEnv::open</a> was called; 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_tx_max</b>
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<p>The DbEnv::get_tx_max method returns the number of active transactions.</p>
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<p>The DbEnv::get_tx_max 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_tx_max 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>tx_maxp</b><ul compact><li>The DbEnv::get_tx_max method returns the
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number of active transactions in <b>tx_maxp</b>.</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>, <a href="../api_cxx/txn_class.html">DbTxn</a>
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<br><b>See Also</b>
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<a href="../api_cxx/txn_list.html">Transaction Subsystem 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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</body>
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</html>
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