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<h2 class="title" style="clear: both"><a id="txn"></a><span class="emphasis"><em>env</em></span> txn</h2>
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<pre class="programlisting">env txn
[-nosync]
[-nowait]
[-parent txnid]
[-sync] </pre>
<p>
The <span class="emphasis"><em>env</em></span> <span class="bold"><strong>txn</strong></span>
command begins a transaction. The returned transaction handle is
bound to a Tcl command of the form <span class="bold"><strong>env.txnX</strong></span>, where X is an integer starting at 0
(for example, env0.txn0 and env0.txn1). It is through this Tcl command
that the script accesses the transaction methods.
</p>
<p>
The options are as follows:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<span class="bold"><strong>-nosync</strong></span>
</p>
<p>
Do not synchronously flush the log when this transaction commits or
prepares. This means the transaction will exhibit the ACI (atomicity,
consistency, and isolation) properties, but not D (durability); that
is, database integrity will be maintained, but it is possible that
this transaction may be undone during recovery instead of being
redone.
</p>
<p>
This behavior may be set for an entire Berkeley DB environment as part
of the <span class="bold"><strong>berkdb env</strong></span> call.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-nowait</strong></span>
</p>
<p>
If a lock is unavailable for any Berkeley DB operation performed in
the context of this transaction, throw a Tcl error immediately instead
of blocking on the lock.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-parent txnid</strong></span>
</p>
<p>
Create the new transaction as a nested transaction, with the specified
transaction indicated as its parent. Transactions may be nested to
any level.
</p>
</li>
<li>
<p>
<span class="bold"><strong>-sync</strong></span>
</p>
<p>
Synchronously flush the log when this transaction commits or prepares.
This means the transaction will exhibit all of the ACID (atomicity,
consistency, isolation, and durability) properties.
</p>
<p>
This behavior is the default for Berkeley DB environments unless the
<span class="bold"><strong>-nosync</strong></span> option was specified to the
<span class="bold"><strong>berkdb env</strong></span> call.
</p>
</li>
</ul>
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<p>
The <span class="emphasis"><em>env</em></span> <span class="bold"><strong>txn</strong></span>
command returns a transaction handle on success.
</p>
<p>
In the case of error, a Tcl error is thrown.
</p>
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