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<h3>DB_ENV->txn_begin</h3>
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<h3><pre>
#include <db.h>
<p>
int
DB_ENV->txn_begin(DB_ENV *env,
DB_TXN *parent, DB_TXN **tid, u_int32_t flags);
</pre></h3>
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<h3>Description: DB_ENV->txn_begin</h3>
<p>The DB_ENV->txn_begin method creates a new transaction in the environment
and copies a pointer to a <a href="../../db43-devel-4.3.21/api_c/txn_class.html">DB_TXN</a> that uniquely identifies it into
the memory to which <b>tid</b> refers. Calling the <a href="../../db43-devel-4.3.21/api_c/txn_abort.html">DB_TXN->abort</a>,
<a href="../../db43-devel-4.3.21/api_c/txn_commit.html">DB_TXN->commit</a> or <a href="../../db43-devel-4.3.21/api_c/txn_discard.html">DB_TXN->discard</a> methods will discard the returned
handle.</p>
<p><b>Note: Transactions may only span threads if they do so serially;
that is, each transaction must be active in only a single thread
of control at a time. This restriction holds for parents of nested
transactions as well; not two children may be concurrently active in
more than one thread of control at any one time.</b></p>
<p><b>Note: Cursors may not span transactions; that is, each cursor must be
opened and closed within a single transaction.</b></p>
<p><b>Note: A parent transaction may not issue any Berkeley DB operations -- except for
DB_ENV->txn_begin, <a href="../../db43-devel-4.3.21/api_c/txn_abort.html">DB_TXN->abort</a> and <a href="../../db43-devel-4.3.21/api_c/txn_commit.html">DB_TXN->commit</a> -- while it has
active child transactions (child transactions that have not yet been
committed or aborted).</b></p>
<p>The DB_ENV->txn_begin method
returns a non-zero error value on failure
and 0 on success.
</p>
<h3>Parameters</h3>
<dl compact>
<dt><b>flags</b><dd>The <b>flags</b> parameter must be set to 0 or by bitwise inclusively <b>OR</b>'ing together one
or more of the following values:
<dl compact>
<dt><a name="DB_DEGREE_2">DB_DEGREE_2</a><dd>This transaction will have degree 2 isolation. This provides for cursor
stability but not repeatable reads. Data items which have been
previously read by this transaction may be deleted or modified by other
transactions before this transaction completes.
<dt><a name="DB_DIRTY_READ">DB_DIRTY_READ</a><dd>All read operations performed by the transaction may read modified but
not yet committed data. Silently ignored if the <a href="../../db43-devel-4.3.21/api_c/db_open.html#DB_DIRTY_READ">DB_DIRTY_READ</a>
flag was not specified when the underlying database was opened.
<dt><a name="DB_TXN_NOSYNC">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); that is,
database integrity will be maintained but it is possible that this
transaction may be undone during recovery.
<p>This behavior may be set for a Berkeley DB environment using the
<a href="../../db43-devel-4.3.21/api_c/env_set_flags.html">DB_ENV->set_flags</a> method. Any value specified to this method
overrides that setting.</p>
<dt><a name="DB_TXN_NOWAIT">DB_TXN_NOWAIT</a><dd>If a lock is unavailable for any Berkeley DB operation performed in the context
of this transaction, cause the operation to
return DB_LOCK_DEADLOCK
immediately instead of blocking on the lock.
<dt><a name="DB_TXN_SYNC">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, isolation, and durability) properties.
<p>This behavior is the default for Berkeley DB environments unless the
<a href="../../db43-devel-4.3.21/api_c/env_set_flags.html#DB_TXN_NOSYNC">DB_TXN_NOSYNC</a> flag was specified to the
<a href="../../db43-devel-4.3.21/api_c/env_set_flags.html">DB_ENV->set_flags</a> method. Any value specified to this method
overrides that setting.</p>
</dl>
<dt><b>parent</b><dd>If the <b>parent</b> parameter 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.
In the presence of distributed transactions and two-phase commit, only
the parental transaction, that is a transaction without a <b>parent</b>
specified, should be passed as an parameter to <a href="../../db43-devel-4.3.21/api_c/txn_prepare.html">DB_TXN->prepare</a>.
</dl>
<h3>Errors</h3>
<p>The DB_ENV->txn_begin method
may fail and return one of the following non-zero errors:</p>
<dl compact>
<dt>ENOMEM<dd>The maximum number of concurrent transactions has been reached.
</dl>
<hr size=1 noshade>
<h3>Class</h3>
<a href="../../db43-devel-4.3.21/api_c/env_class.html">DB_ENV</a>, <a href="../../db43-devel-4.3.21/api_c/txn_class.html">DB_TXN</a>
<h3>See Also</h3>
<a href="../../db43-devel-4.3.21/api_c/txn_list.html">Transaction Subsystem and Related Methods</a>
</tt>
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