1<!--$Id: env_set_tx_max.so,v 10.47 2006/06/19 22:25:31 bostic Exp $--> 2<!--Copyright (c) 1997,2008 Oracle. All rights reserved.--> 3<!--See the file LICENSE for redistribution information.--> 4<html> 5<head> 6<title>Berkeley DB: DbEnv::set_tx_max</title> 7<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> 8<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> 9</head> 10<body bgcolor=white> 11<table width="100%"><tr valign=top> 12<td> 13<b>DbEnv::set_tx_max</b> 14</td> 15<td align=right> 16<a href="/api_cxx/api_core.html"><img src="/images/api.gif" alt="API"></a> 17<a href="/ref/toc.html"><img src="/images/ref.gif" alt="Ref"></a></td> 18</tr></table> 19<hr size=1 noshade> 20<tt> 21<b><pre> 22#include <db_cxx.h> 23<p> 24int 25DbEnv::set_tx_max(u_int32_t max); 26<p> 27int 28DbEnv::get_tx_max(u_int32_t *tx_maxp); 29</pre></b> 30<hr size=1 noshade> 31<b>Description: DbEnv::set_tx_max</b> 32<p>Configure the Berkeley DB database environment to support at least <b>max</b> 33active transactions. This value bounds the size of the memory allocated 34for transactions. Child transactions are counted as active until they 35either commit or abort.</p> 36<p>Transactions that update multiversion databases are not freed until the 37last page version that the transaction created is flushed from cache. 38This means that applications using multi-version concurrency control may 39need a transaction for each page in cache, in the extreme case.</p> 40<p>When all of the memory available in the database environment for 41transactions is in use, calls to <a href="/api_cxx/txn_begin.html">DbEnv::txn_begin</a> will fail (until some 42active transactions complete). If this interface is never called, the 43database environment is configured to support at least 100 active 44transactions.</p> 45<p>The database environment's number of active transactions may also be configured using the 46environment's <a href="/ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> file. The syntax of the entry in that 47file is a single line with the string "set_tx_max", one or more whitespace 48characters, and the number of transactions. 49Because the <a href="/ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> file is read when the database environment 50is opened, it will silently overrule configuration done before that 51time.</p> 52<p>The DbEnv::set_tx_max method configures a database environment, not only operations 53performed using the specified <a href="/api_cxx/env_class.html">DbEnv</a> handle.</p> 54<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 55called. 56If the database environment already exists when 57<a href="/api_cxx/env_open.html">DbEnv::open</a> is called, the information specified to DbEnv::set_tx_max 58will be ignored. 59</p> 60<p>The DbEnv::set_tx_max method 61either returns a non-zero error value 62or throws an exception that encapsulates a non-zero error value on 63failure, and returns 0 on success. 64</p> 65<b>Parameters</b> <br> 66 <b>max</b><ul compact><li>The <b>max</b> parameter configures the minimum number of 67simultaneously active transactions supported by Berkeley DB database 68environment.</ul> 69<br> 70<br><b>Errors</b> 71<p>The DbEnv::set_tx_max method 72may fail and throw 73<a href="/api_cxx/except_class.html">DbException</a>, 74encapsulating one of the following non-zero errors, or return one of 75the following non-zero errors:</p> 76<br> 77<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 78invalid flag value or parameter was specified.</ul> 79<br> 80<hr size=1 noshade> 81<b>Description: DbEnv::get_tx_max</b> 82<p>The DbEnv::get_tx_max method returns the number of active transactions.</p> 83<p>The DbEnv::get_tx_max method may be called at any time during the life of the 84application.</p> 85<p>The DbEnv::get_tx_max method 86either returns a non-zero error value 87or throws an exception that encapsulates a non-zero error value on 88failure, and returns 0 on success. 89</p> 90<b>Parameters</b> <br> 91 <b>tx_maxp</b><ul compact><li>The DbEnv::get_tx_max method returns the 92number of active transactions in <b>tx_maxp</b>.</ul> 93<br> 94<hr size=1 noshade> 95<br><b>Class</b> 96<a href="/api_cxx/env_class.html">DbEnv</a>, <a href="/api_cxx/txn_class.html">DbTxn</a> 97<br><b>See Also</b> 98<a href="/api_cxx/txn_list.html">Transaction Subsystem and Related Methods</a> 99</tt> 100<table width="100%"><tr><td><br></td><td align=right> 101<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> 102</td></tr></table> 103<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font> 104</body> 105</html> 106
