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14<b><i>env</i> <b>txn</b></b>
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22<b><pre>env txn
23	[-nosync]
24	[-nowait]
25	[-parent txnid]
26	[-sync]
27</pre></b>
28<b>Description(env txn)</b>
29<p>The <i>env</i> <b>txn</b> command begins a transaction.  The returned transaction
30handle is bound to a Tcl command of the form <b>env.txnX</b>, where
31X is an integer starting at 0 (for example, env0.txn0 and env0.txn1).
32It is through this Tcl command that the script accesses the transaction
33methods.</p>
34<p>The options are as follows:</p>
35<br>
36<b>-nosync</b><ul compact><li>Do not synchronously flush the log when this transaction commits or
37prepares. This means the transaction will exhibit the ACI (atomicity,
38consistency, and isolation) properties, but not D (durability); that
39is, database integrity will be maintained, but it is possible that this
40transaction may be undone during recovery instead of being redone.
41<p>This behavior may be set for an entire Berkeley DB environment as part of the
42<b>berkdb env</b> call.</p></ul>
43<b>-nowait</b><ul compact><li>If a lock is unavailable for any Berkeley DB operation performed in the context
44of this transaction, throw a Tcl error immediately instead of blocking on
45the lock.</ul>
46<b>-parent txnid</b><ul compact><li>Create the new transaction as a nested transaction, with the specified
47transaction indicated as its parent.  Transactions may be nested to any
48level.</ul>
49<b>-sync</b><ul compact><li>Synchronously flush the log when this transaction commits or prepares.
50This means the transaction will exhibit all of the ACID (atomicity,
51consistency, isolation, and durability) properties.
52<p>This behavior is the default for Berkeley DB environments unless the
53<b>-nosync</b> option was specified to the <b>berkdb env</b> call.</p></ul>
54<br>
55<p>The <i>env</i> <b>txn</b> command returns a transaction handle on success.</p>
56<p>In the case of error, a Tcl error is thrown.</p>
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