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<h2 class="title" style="clear: both"><a id="envset_tx_max"></a>DB_ENV->set_tx_max()</h2>
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<pre class="programlisting">#include <db.h>
int
DB_ENV->set_tx_max(DB_ENV *dbenv, u_int32_t max); </pre>
<p>
Configure the Berkeley DB database environment to support at least
<span class="bold"><strong>max</strong></span> active transactions. This value
bounds the size of the memory allocated for transactions. Child
transactions are counted as active until they either commit or abort.
</p>
<p>
Transactions that update multiversion databases are not freed until
the last page version that the transaction created is flushed from
cache. This means that applications using multi-version concurrency
control may need a transaction for each page in cache, in the extreme
case.
</p>
<p>
When all of the memory available in the database environment for
transactions is in use, calls to
<a class="xref" href="txnbegin.html" title="DB_ENV->txn_begin()">DB_ENV->txn_begin()</a> will fail
(until some active transactions complete). If
<code class="classname">DB_ENV->set_tx_max()</code> is never called,
the database environment is configured to support at least 100
active transactions.
</p>
<p>
The database environment's number of active transactions may also be
configured using the environment's <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> file. The
syntax of the entry in that file is a single line with the string
"set_tx_max", one or more whitespace characters, and the number of
transactions. Because the <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> file is
read when the database environment is opened, it will silently
overrule configuration done before that time.
</p>
<p>
The <code class="methodname">DB_ENV->set_tx_max()</code> method configures a database environment,
not only operations performed using the specified
<a class="link" href="env.html" title="Chapter 5. The DB_ENV Handle">DB_ENV</a> handle.
</p>
<p>
The <code class="methodname">DB_ENV->set_tx_max()</code> method may not be called after the
<a class="xref" href="envopen.html" title="DB_ENV->open()">DB_ENV->open()</a> method is called.
If the database environment already exists when
<a class="xref" href="envopen.html" title="DB_ENV->open()">DB_ENV->open()</a> is called, the
information specified to <code class="methodname">DB_ENV->set_tx_max()</code> will be ignored.
</p>
<p>
The <code class="methodname">DB_ENV->set_tx_max()</code> <span>
<span>
method returns a non-zero error value on failure and 0 on success.
</span>
</span>
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1707414"></a>Parameters</h3>
</div>
</div>
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<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1707828"></a>max</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>max</strong></span> parameter configures the
minimum number of simultaneously active transactions supported by
Berkeley DB database environment.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1707416"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">DB_ENV->set_tx_max()</code> <span>
<span>
method may fail and return one of the following non-zero errors:
</span>
</span>
</p>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1707608"></a>EINVAL</h4>
</div>
</div>
</div>
<p>
If the method was called after <a class="xref" href="envopen.html" title="DB_ENV->open()">DB_ENV->open()</a>
was called; or if an invalid flag value or parameter was specified.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1707973"></a>Class</h3>
</div>
</div>
</div>
<p>
<a class="link" href="env.html" title="Chapter 5. The DB_ENV Handle">DB_ENV</a>,
<a class="link" href="txn.html" title="Chapter 12. The DB_TXN Handle">DB_TXN</a>
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1707905"></a>See Also</h3>
</div>
</div>
</div>
<p>
<a class="xref" href="txn.html#txnlist" title="Transaction Subsystem and Related Methods">Transaction Subsystem and Related Methods</a>
</p>
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