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<!--$Id: txn_begin.so,v 10.37 2001/01/11 17:47:12 bostic Exp $-->
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<!--Copyright 1997, 1998, 1999, 2000 by Sleepycat Software, Inc.-->
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<html>
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<title>Berkeley DB: DbEnv.txn_begin</title>
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<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,java,C,C++">
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<a name="2"><!--meow--></a>
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<table><tr valign=top>
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<td>
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<h1>DbEnv.txn_begin</h1>
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</td>
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<td width="1%">
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<a href="../api_java/java_index.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a>
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</td></tr></table>
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<tt>
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<h3><pre>
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import com.sleepycat.db.*;
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<p>
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public DbTxn txn_begin(DbTxn parent, int flags)
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throws DbException;
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</pre></h3>
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<h1>Description</h1>
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<p>The DbEnv.txn_begin method creates a new transaction in the environment
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and returns a <a href="../api_java/txn_class.html">DbTxn</a> that uniquely identifies it.
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<p>If the <b>parent</b> argument is non-null, the new transaction will
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be a nested transaction, with the transaction indicated by
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<b>parent</b> as its parent. Transactions may be
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nested to any level.
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<p>The <b>flags</b> parameter must be set to 0 or one of the following
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values:
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<p><dl compact>
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<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
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prepares. This means the transaction will exhibit the ACI (atomicity,
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consistency and isolation) properties, but not D (durability), i.e.,
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database integrity will be maintained but it is possible that this
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transaction may be undone during recovery instead of being redone.
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<p>This behavior may be set for an entire Berkeley DB environment as part of the
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<a href="../api_java/env_set_flags.html">DbEnv.set_flags</a> interface.
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<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
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of this transaction, return immediately instead of blocking on the lock.
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The error return in the case will be <a href="../ref/program/errorret.html#DB_LOCK_NOTGRANTED">Db.DB_LOCK_NOTGRANTED</a>.
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<p><dt><a name="Db.DB_TXN_SYNC">Db.DB_TXN_SYNC</a><dd>Synchronously flush the log when this transaction commits or prepares.
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This means the transaction will exhibit all of the ACID (atomicity,
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consistency and isolation and durability) properties.
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<p>This behavior is the default for Berkeley DB environments unless the
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<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>
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interface.
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</dl>
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<p><b>Note: An transaction may not span threads,
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i.e., each transaction must begin and end in the same thread, and each
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transaction may only be used by a single thread.</b>
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<p><b>Note: cursors may not span transactions, i.e., each cursor must be opened
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and closed within a single transaction.</b>
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<p><b>Note: a parent transaction may not issue any Berkeley DB operations, except for
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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
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active child transactions (child transactions that have not yet been
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committed or aborted).</b>
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<p>The DbEnv.txn_begin method throws an exception that encapsulates a non-zero error value on
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failure.
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<h1>Errors</h1>
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<p>The DbEnv.txn_begin method may fail and throw an exception encapsulating a non-zero error for the following conditions:
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<p><dl compact>
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<p><dt>ENOMEM<dd>The maximum number of concurrent transactions has been reached.
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</dl>
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<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.
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If a catastrophic error has occurred, the DbEnv.txn_begin method may fail and throw
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a <a href="../api_java/runrec_class.html">DbRunRecoveryException</a>, in which case all subsequent Berkeley DB calls
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will fail in the same way.
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<h3>Classes</h3>
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<a href="../api_java/dbenv_class.html">DbEnv</a>, <a href="../api_java/txn_class.html">DbTxn</a>
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<h1>See Also</h1>
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<a href="../api_java/env_set_tx_max.html">DbEnv.set_tx_max</a>,
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<a href="../api_java/env_set_tx_timestamp.html">DbEnv.set_tx_timestamp</a>,
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<a href="../api_java/txn_abort.html">DbTxn.abort</a>,
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<a href="../api_java/txn_begin.html">DbEnv.txn_begin</a>,
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<a href="../api_java/txn_checkpoint.html">DbEnv.txn_checkpoint</a>,
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<a href="../api_java/txn_commit.html">DbTxn.commit</a>,
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<a href="../api_java/txn_id.html">DbTxn.id</a>,
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<a href="../api_java/txn_prepare.html">DbTxn.prepare</a>
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and
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<a href="../api_java/txn_stat.html">DbEnv.txn_stat</a>.
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</tt>
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<table><tr><td><br></td><td width="1%">
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<a href="../api_java/java_index.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a>
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