2
<!--Copyright 1997-2002 by Sleepycat Software, Inc.-->
3
<!--All rights reserved.-->
4
<!--See the file LICENSE for redistribution information.-->
7
<title>Berkeley DB: DB_ENV->txn_begin</title>
8
<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
9
<meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,java,C,C++">
12
<a name="2"><!--meow--></a>
13
<table width="100%"><tr valign=top>
15
<h1>DB_ENV->txn_begin</h1>
18
<a href="../api_c/c_index.html"><img src="../images/api.gif" alt="API"></a><a href="../reftoc.html"><img src="../images/ref.gif" alt="Ref"></a>
26
DB_ENV->txn_begin(DB_ENV *env,
27
DB_TXN *parent, DB_TXN **tid, u_int32_t flags);
30
<p>The DB_ENV->txn_begin method creates a new transaction in the environment
31
and copies a pointer to a <a href="../api_c/txn_class.html">DB_TXN</a> that uniquely identifies it into
32
the memory to which <b>tid</b> refers.
33
Calling the <a href="../api_c/txn_abort.html">DB_TXN->abort</a>,
34
<a href="../api_c/txn_commit.html">DB_TXN->commit</a> or <a href="../api_c/txn_discard.html">DB_TXN->discard</a> methods will discard the returned
36
<p>If the <b>parent</b> argument is non-NULL, the new transaction will
37
be a nested transaction, with the transaction indicated by
38
<b>parent</b> as its parent. Transactions may be
40
In the presence of distributed transactions and two-phase commit,
41
only the parental transaction, that is a transaction without
42
a <b>parent</b> specified, should be passed as an argument to
43
<a href="../api_c/txn_prepare.html">DB_TXN->prepare</a>.
44
<p>The <b>flags</b> value must be set to 0 or by bitwise inclusively <b>OR</b>'ing together one or
45
more of the following values:
47
<p><dt><a name="DB_DIRTY_READ">DB_DIRTY_READ</a><dd>All read operations performed by the transaction will read modified but
48
not yet committed data. Silently ignored if the <a href="../api_c/db_open.html#DB_DIRTY_READ">DB_DIRTY_READ</a>
49
flag was not specified when the underlying database was opened.
50
<p><dt><a name="DB_TXN_NOSYNC">DB_TXN_NOSYNC</a><dd>Do not synchronously flush the log when this transaction commits or
51
prepares. This means the transaction will exhibit the ACI (atomicity,
52
consistency, and isolation) properties, but not D (durability); that is,
53
database integrity will be maintained but it is possible that this
54
transaction may be undone during recovery.
55
<p>This behavior may be set for a Berkeley DB environment using the
56
<a href="../api_c/env_set_flags.html">DB_ENV->set_flags</a> interface. Any value specified in this
57
interface overrides that setting.
58
<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
60
return DB_LOCK_NOTGRANTED
61
immediately instead of blocking on the lock.
62
<p><dt><a name="DB_TXN_SYNC">DB_TXN_SYNC</a><dd>Synchronously flush the log when this transaction commits or prepares.
63
This means the transaction will exhibit all of the ACID (atomicity,
64
consistency, isolation, and durability) properties.
65
<p>This behavior is the default for Berkeley DB environments unless the
66
<a href="../api_c/env_set_flags.html#DB_TXN_NOSYNC">DB_TXN_NOSYNC</a> flag was specified to the <a href="../api_c/env_set_flags.html">DB_ENV->set_flags</a>
67
interface. Any value specified in this interface overrides that
70
<p><b>Note: A transaction may not span threads; that is, each transaction must
71
begin and end in the same thread, and each transaction may be used only
72
by a single thread.</b>
73
<p><b>Note: Cursors may not span transactions; that is, each cursor must be
74
opened and closed within a single transaction.</b>
75
<p><b>Note: A parent transaction may not issue any Berkeley DB operations -- except for
76
DB_ENV->txn_begin, <a href="../api_c/txn_abort.html">DB_TXN->abort</a> and <a href="../api_c/txn_commit.html">DB_TXN->commit</a> -- while it has
77
active child transactions (child transactions that have not yet been
78
committed or aborted).</b>
79
<p>The DB_ENV->txn_begin method returns a non-zero error value on failure and 0 on success.
81
<p>The DB_ENV->txn_begin method may fail and return a non-zero error for the following conditions:
83
<p><dt>ENOMEM<dd>The maximum number of concurrent transactions has been reached.
85
<p>The DB_ENV->txn_begin method may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions.
86
If a catastrophic error has occurred, the DB_ENV->txn_begin method may fail and
87
return <a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a>,
88
in which case all subsequent Berkeley DB calls will fail in the same way.
90
<a href="../api_c/env_class.html">DB_ENV</a>, <a href="../api_c/txn_class.html">DB_TXN</a>
92
<a href="../api_c/txn_list.html">Transaction Subsystem and Related Methods</a>
94
<table width="100%"><tr><td><br></td><td align=right>
95
<a href="../api_c/c_index.html"><img src="../images/api.gif" alt="API"></a><a href="../reftoc.html"><img src="../images/ref.gif" alt="Ref"></a>
97
<p><font size=1><a href="http://www.sleepycat.com">Copyright Sleepycat Software</a></font>