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<h1>DbEnv.txn_begin</h1>
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<h3><pre>
import com.sleepycat.db.*;
<p>
public DbTxn txn_begin(DbTxn parent, int flags)
throws DbException;
</pre></h3>
<h1>Description</h1>
<p>The DbEnv.txn_begin method creates a new transaction in the environment
and returns a <a href="../api_java/txn_class.html">DbTxn</a> that uniquely identifies it.
<p>If the <b>parent</b> argument is non-null, the new transaction will
be a nested transaction, with the transaction indicated by
<b>parent</b> as its parent. Transactions may be
nested to any level.
<p>The <b>flags</b> parameter must be set to 0 or one of the following
values:
<p><dl compact>
<p><dt><a name="Db.DB_TXN_NOSYNC">Db.DB_TXN_NOSYNC</a><dd>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), i.e.,
database integrity will be maintained but it is possible that this
transaction may be undone during recovery instead of being redone.
<p>This behavior may be set for an entire Berkeley DB environment as part of the
<a href="../api_java/env_set_flags.html">DbEnv.set_flags</a> interface.
<p><dt><a name="Db.DB_TXN_NOWAIT">Db.DB_TXN_NOWAIT</a><dd>If a lock is unavailable for any Berkeley DB operation performed in the context
of this transaction, return immediately instead of blocking on the lock.
The error return in the case will be <a href="../ref/program/errorret.html#DB_LOCK_NOTGRANTED">Db.DB_LOCK_NOTGRANTED</a>.
<p><dt><a name="Db.DB_TXN_SYNC">Db.DB_TXN_SYNC</a><dd>Synchronously flush the log when this transaction commits or prepares.
This means the transaction will exhibit all of the ACID (atomicity,
consistency and isolation and durability) properties.
<p>This behavior is the default for Berkeley DB environments unless the
<a href="../api_java/env_open.html#DB_TXN_NOSYNC">Db.DB_TXN_NOSYNC</a> flag was specified to the <a href="../api_java/env_set_flags.html">DbEnv.set_flags</a>
interface.
</dl>
<p><b>Note: An transaction may not span threads,
i.e., each transaction must begin and end in the same thread, and each
transaction may only be used by a single thread.</b>
<p><b>Note: cursors may not span transactions, i.e., each cursor must be opened
and closed within a single transaction.</b>
<p><b>Note: a parent transaction may not issue any Berkeley DB operations, except for
DbEnv.txn_begin, <a href="../api_java/txn_abort.html">DbTxn.abort</a> and <a href="../api_java/txn_commit.html">DbTxn.commit</a>, while it has
active child transactions (child transactions that have not yet been
committed or aborted).</b>
<p>The DbEnv.txn_begin method throws an exception that encapsulates a non-zero error value on
failure.
<h1>Errors</h1>
<p>The DbEnv.txn_begin method may fail and throw an exception encapsulating a non-zero error for the following conditions:
<p><dl compact>
<p><dt>ENOMEM<dd>The maximum number of concurrent transactions has been reached.
</dl>
<p>The DbEnv.txn_begin method may fail and throw an exception for errors specified for other Berkeley DB and C library or system methods.
If a catastrophic error has occurred, the DbEnv.txn_begin method may fail and throw
a <a href="../api_java/runrec_class.html">DbRunRecoveryException</a>, in which case all subsequent Berkeley DB calls
will fail in the same way.
<h3>Classes</h3>
<a href="../api_java/dbenv_class.html">DbEnv</a>, <a href="../api_java/txn_class.html">DbTxn</a>
<h1>See Also</h1>
<a href="../api_java/env_set_tx_max.html">DbEnv.set_tx_max</a>,
<a href="../api_java/env_set_tx_timestamp.html">DbEnv.set_tx_timestamp</a>,
<a href="../api_java/txn_abort.html">DbTxn.abort</a>,
<a href="../api_java/txn_begin.html">DbEnv.txn_begin</a>,
<a href="../api_java/txn_checkpoint.html">DbEnv.txn_checkpoint</a>,
<a href="../api_java/txn_commit.html">DbTxn.commit</a>,
<a href="../api_java/txn_id.html">DbTxn.id</a>,
<a href="../api_java/txn_prepare.html">DbTxn.prepare</a>
and
<a href="../api_java/txn_stat.html">DbEnv.txn_stat</a>.
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