DbEnv::set_flags(u_int32_t flags, int onoff); </pre>
<p>
Configure a database environment.
</p>
<p>
The database environment's flag values may also be configured
using the environment's <ahref="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG"class="olink">DB_CONFIG</a> file. The syntax of the entry
in that file is a single line with the string "set_flags", one or
more whitespace characters, and the method flag parameter as a
string, and optionally one or more whitespace characters, and the
string "on" or "off". If the optional string is omitted, the
default is "on"; for example, "set_flags DB_TXN_NOSYNC" or
"set_flags DB_TXN_NOSYNC on". Because the <ahref="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG"class="olink">DB_CONFIG</a> file is read
when the database environment is opened, it will silently overrule
configuration done before that time.
</p>
<p>
The <codeclass="methodname">DbEnv::set_flags()</code><span>
<span>
method either returns a non-zero error value or throws an
exception that encapsulates a non-zero error value on
The <aclass="xref"href="db_hotbackup.html"title="db_hotbackup">db_hotbackup</a>
utility implements the protocol described above.
</p>
</li>
<li>
<p><aid="set_flags_DB_DSYNC_DB"></a>
<codeclass="literal">DB_DSYNC_DB</code>
</p>
<p>
Configure Berkeley DB to flush database writes to the backing disk
before returning from the write system call, rather than flushing
database writes explicitly in a separate system call, as necessary.
This is only available on some systems (for example, systems
supporting the IEEE/ANSI Std 1003.1 (POSIX) standard O_DSYNC flag, or
systems supporting the Windows FILE_FLAG_WRITE_THROUGH flag). This
flag may result in inaccurate file modification times and other
file-level information for Berkeley DB database files. This flag will
almost certainly result in a performance decrease on most systems.
This flag is only applicable to certain filesysystems (for example, the
Veritas VxFS filesystem), where the filesystem's support for trickling
writes back to stable storage behaves badly (or more likely, has been
misconfigured).
</p>
<p>
Calling <codeclass="methodname">DbEnv::set_flags()</code> with the DB_DSYNC_DB flag only affects
the specified <aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a>
handle (and any other Berkeley DB handles opened within the scope of
that handle). For consistent behavior across the environment, all
<aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a> handles opened in
the environment must either set the DB_DSYNC_DB flag or the flag
should be specified in the <ahref="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG"class="olink">DB_CONFIG</a> configuration file.
</p>
<p>
The DB_DSYNC_DB flag may be used to configure Berkeley DB at any time
during the life of the application.
</p>
</li>
<li>
<p><aid="set_flags_DB_MULTIVERSION"></a>
<codeclass="literal">DB_MULTIVERSION</code>
</p>
<p>
If set, all databases in the environment will be opened as if
DB_MULTIVERSION is passed to the <aclass="xref"href="dbopen.html"title="Db::open()">Db::open()</a>
method. This flag will be ignored for queue databases for which DB_MULTIVERSION is not
supported.
</p>
<p>
Calling <codeclass="methodname">DbEnv::set_flags()</code> with the DB_MULTIVERSION flag only
affects the specified <aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a> handle (and any other
Berkeley DB handles opened within the scope of that handle). For
consistent behavior across the environment, all <aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a>
handles opened in the environment must either set the DB_MULTIVERSION flag or the flag
Calling <codeclass="methodname">DbEnv::set_flags()</code> with the DB_PANIC_ENVIRONMENT flag
affects the database environment, including all threads of control
accessing the database environment.
</p>
<p>
The DB_PANIC_ENVIRONMENT flag may be used to configure Berkeley DB
only after the <aclass="xref"href="envopen.html"title="DbEnv::open()">DbEnv::open()</a> method is called.
</p>
</li>
<li>
<p><aid="set_flags_DB_REGION_INIT"></a>
<codeclass="literal">DB_REGION_INIT</code>
</p>
<p>
In some applications, the expense of page-faulting the underlying
shared memory regions can affect performance. (For example, if the
page-fault occurs while holding a lock, other lock requests can
convoy, and overall throughput may decrease.) If set, Berkeley DB
will page-fault shared regions into memory when initially creating or
joining a Berkeley DB environment. In addition, Berkeley DB will
write the shared regions when creating an environment, forcing the
underlying virtual memory and filesystems to instantiate both the
necessary memory and the necessary disk space. This can also avoid
out-of-disk space failures later on.
</p>
<p>
Calling <codeclass="methodname">DbEnv::set_flags()</code> with the DB_REGION_INIT flag only affects
the specified <aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a>
handle (and any other Berkeley DB handles opened within the scope of
that handle). For consistent behavior across the environment, all
<aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a> handles opened in
the environment must either set the DB_REGION_INIT flag or the flag
should be specified in the <ahref="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG"class="olink">DB_CONFIG</a> configuration file.
</p>
<p>
The DB_REGION_INIT flag may be used to configure Berkeley DB at any
time during the life of the application.
</p>
</li>
<li>
<p><aid="envset_flags_DB_TIME_NOTGRANTED"></a>
<codeclass="literal">DB_TIME_NOTGRANTED</code>
</p>
<p>
If set, database calls timing out based on lock or transaction timeout
This allows applications to distinguish between operations which have
deadlocked and operations which have exceeded their time limits.
</p>
<p>
Calling <codeclass="methodname">DbEnv::set_flags()</code> with the DB_TIME_NOTGRANTED flag only
affects the specified <aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a> handle (and any other
Berkeley DB handles opened within the scope of that handle). For
consistent behavior across the environment, all
<aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a> handles opened in the
environment must either set the DB_TIME_NOTGRANTED flag or the flag
should be specified in the <ahref="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG"class="olink">DB_CONFIG</a> configuration file.
</p>
<p>
The <codeclass="literal">DB_TIME_NOTGRANTED</code> flag may be used to configure Berkeley DB at
any time during the life of the application.
</p>
<p>
Note that the <aclass="xref"href="lockget.html"title="DbEnv::lock_get()">DbEnv::lock_get()</a>
and <aclass="xref"href="lockvec.html"title="DbEnv::lock_vec()">DbEnv::lock_vec()</a>
methods are unaffected by this flag.
</p>
</li>
<li>
<p><aid="envset_flags_DB_TXN_NOSYNC"></a>
<codeclass="literal">DB_TXN_NOSYNC</code>
</p>
<p>
If set, Berkeley DB will not write or synchronously flush the log on
transaction commit. This means that transactions exhibit the ACI
(atomicity, consistency, and isolation) properties, but not D
(durability); that is, database integrity will be maintained, but if
the application or system fails, it is possible some number of the
most recently committed transactions may be undone during recovery.
The number of transactions at risk is governed by how many log updates
can fit into the log buffer, how often the operating system flushes
dirty buffers to disk, and how often the log is checkpointed.
</p>
<p>
Calling <codeclass="methodname">DbEnv::set_flags()</code> with the DB_TXN_NOSYNC flag only affects
the specified <aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a>
handle (and any other Berkeley DB handles opened within the scope of
that handle). For consistent behavior across the environment, all
<aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a> handles opened in
the environment must either set the DB_TXN_NOSYNC flag or the flag
should be specified in the <ahref="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG"class="olink">DB_CONFIG</a> configuration file.
</p>
<p>
The DB_TXN_NOSYNC flag may be used to configure Berkeley DB at any
time during the life of the application.
</p>
</li>
<li>
<p><aid="set_flags_DB_TXN_NOWAIT"></a>
<codeclass="literal">DB_TXN_NOWAIT</code>
</p>
<p>
If set and a lock is unavailable for any Berkeley DB operation
performed in the context of a transaction, cause the operation to
Calling <codeclass="methodname">DbEnv::set_flags()</code> with the DB_TXN_NOWAIT flag only affects
the specified <aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a>
handle (and any other Berkeley DB handles opened within the scope of
that handle). For consistent behavior across the environment, all
<aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a> handles opened in
the environment must either set the DB_TXN_NOWAIT flag or the flag
should be specified in the <ahref="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG"class="olink">DB_CONFIG</a> configuration file.
</p>
<p>
The DB_TXN_NOWAIT flag may be used to configure Berkeley DB at any
time during the life of the application.
</p>
</li>
<li>
<p><aid="set_flags_DB_TXN_SNAPSHOT"></a>
<codeclass="literal">DB_TXN_SNAPSHOT</code>
</p>
<p>
If set, all transactions in the environment will be started as if
DB_TXN_SNAPSHOT were passed to the
<aclass="xref"href="txnbegin.html"title="DbEnv::txn_begin()">DbEnv::txn_begin()</a> method, and all
non-transactional cursors will be opened as if DB_TXN_SNAPSHOT were
passed to the <aclass="xref"href="dbcursor.html"title="Db::cursor()">Db::cursor()</a> method.
</p>
<p>
Calling <codeclass="methodname">DbEnv::set_flags()</code> with the DB_TXN_SNAPSHOT flag only
affects the specified <aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a>
handle (and any other Berkeley DB handles opened within the scope of that handle). For
consistent behavior across the environment, all
<aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a> handles opened in the
environment must either set the DB_TXN_SNAPSHOT flag or the flag
should be specified in the <ahref="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG"class="olink">DB_CONFIG</a> configuration file.
</p>
<p>
The DB_TXN_SNAPSHOT flag may be used to configure Berkeley DB at any
time during the life of the application.
</p>
</li>
<li>
<p><aid="set_flags_DB_TXN_WRITE_NOSYNC"></a>
<codeclass="literal">DB_TXN_WRITE_NOSYNC</code>
</p>
<p>
If set, Berkeley DB will write, but will not synchronously flush, the
log on transaction commit. This means that transactions exhibit the
ACI (atomicity, consistency, and isolation) properties, but not D
(durability); that is, database integrity will be maintained, but if
the system fails, it is possible some number of the most recently
committed transactions may be undone during recovery. The number of
transactions at risk is governed by how often the system flushes dirty
buffers to disk and how often the log is checkpointed.
</p>
<p>
Calling <codeclass="methodname">DbEnv::set_flags()</code> with the DB_TXN_WRITE_NOSYNC flag only
affects the specified <aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a>
handle (and any other Berkeley DB handles opened within the scope of that handle). For
consistent behavior across the environment, all
<aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a> handles opened in the
environment must either set the DB_TXN_WRITE_NOSYNC flag or the flag
should be specified in the <ahref="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG"class="olink">DB_CONFIG</a> configuration file.
</p>
<p>
The DB_TXN_WRITE_NOSYNC flag may be used to configure Berkeley DB at
any time during the life of the application.
</p>
</li>
<li>
<p><aid="set_flags_DB_YIELDCPU"></a>
<codeclass="literal">DB_YIELDCPU</code>
</p>
<p>
If set, Berkeley DB will yield the processor immediately after each
page or mutex acquisition. This functionality should never be used
for purposes other than stress testing.
</p>
<p>
Calling <codeclass="methodname">DbEnv::set_flags()</code> with the DB_YIELDCPU flag only affects
the specified <aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a>
handle (and any other Berkeley DB handles opened within the scope of
that handle). For consistent behavior across the environment, all
<aclass="link"href="env.html"title="Chapter5. The DbEnv Handle">DbEnv</a> handles opened in
the environment must either set the DB_YIELDCPU flag or the flag
should be specified in the <ahref="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG"class="olink">DB_CONFIG</a> configuration file.
</p>
<p>
The DB_YIELDCPU flag may be used to configure Berkeley DB at any time
