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<th colspan="3" align="center">DbEnv::log_set_config()</th>
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<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="envlog_set_config"></a>DbEnv::log_set_config()</h2>
</div>
</div>
</div>
<pre class="programlisting">#include <db_cxx.h>
int
DbEnv::log_set_config(u_int32_t flags, int onoff); </pre>
<p>
The <code class="methodname">DbEnv::log_set_config()</code> method configures the Berkeley DB
logging subsystem.
</p>
<p>
The <code class="methodname">DbEnv::log_set_config()</code> method configures a database
environment, not only operations performed using the specified
<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> handle.
</p>
<p>
The <code class="methodname">DbEnv::log_set_config()</code> method may be called at any time during
the life of the application.
</p>
<p>
The <code class="methodname">DbEnv::log_set_config()</code> <span>
<span>
method either returns a non-zero error value or throws an
exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
</span>
</span>
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp8376264"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp8370056"></a>flags</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>flags</strong></span> parameter must be set by
bitwise inclusively <span class="bold"><strong>OR</strong></span>'ing together
one or more of the following values:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p><a id="log_set_config_DB_LOG_DIRECT"></a>
<code class="literal">DB_LOG_DIRECT</code>
</p>
<p>
Turn off system buffering of Berkeley DB log files to avoid double
caching.
</p>
<p>
Calling <code class="methodname">DbEnv::log_set_config()</code> with the DB_LOG_DIRECT flag only
affects the specified <a class="link" href="env.html" title="Chapter 5. 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
<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> handles opened in the
environment must either set the DB_LOG_DIRECT flag or the flag should
be specified in the <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> configuration file.
</p>
<p>
The <code class="literal">DB_LOG_DIRECT</code> flag may be used to configure Berkeley DB at any
time during the life of the application.
</p>
</li>
<li>
<p><a id="log_set_config_DB_LOG_DSYNC"></a>
<code class="literal">DB_LOG_DSYNC</code>
</p>
<p>
Configure Berkeley DB to flush log writes to the backing disk before
returning from the write system call, rather than flushing log 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 log files. This flag may offer a
performance increase on some systems and a performance decrease on
others.
</p>
<p>
Calling <code class="methodname">DbEnv::log_set_config()</code> with the DB_LOG_DSYNC flag only
affects the specified <a class="link" href="env.html" title="Chapter 5. 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
<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> handles opened in the
environment must either set the DB_LOG_DSYNC flag or the flag should
be specified in the <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> configuration file.
</p>
<p>
The <code class="literal">DB_LOG_DSYNC</code> flag may be used to configure Berkeley DB at any time
during the life of the application.
</p>
</li>
<li>
<p><a id="log_set_config_DB_LOG_AUTO_REMOVE"></a>
<code class="literal">DB_LOG_AUTO_REMOVE</code>
</p>
<p>
If set, Berkeley DB will automatically remove log files that are no
longer needed.
</p>
<p>
Automatic log file removal is likely to make catastrophic recovery
impossible.
</p>
<p>
Replication Manager applications operate in a
group-aware manner for log file removal, and automatic log
file removal simplifies the application.
</p>
<p>
Replication Base API applications will rarely want to configure automatic log
file removal as it increases the likelihood a master will be unable to
satisfy a client's request for a recent log record.
</p>
<p>
Calling <code class="methodname">DbEnv::log_set_config()</code> with the
<code class="literal">DB_LOG_AUTO_REMOVE</code> flag
affects the database environment, including all threads of control
accessing the database environment.
</p>
<p>
The <code class="literal">DB_LOG_AUTO_REMOVE</code> flag may be used to configure Berkeley DB at
any time during the life of the application.
</p>
</li>
<li>
<p><a id="log_set_config_DB_LOG_IN_MEMORY"></a>
<code class="literal">DB_LOG_IN_MEMORY</code>
</p>
<p>
If set, maintain transaction logs in memory rather than on disk. 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,
integrity will not persist. All database files must be verified
and/or restored from a replication group master or archival backup
after application or system failure.
</p>
<p>
When in-memory logs are configured and no more log buffer space is
available, Berkeley DB methods may return an additional error value,
<code class="literal">DB_LOG_BUFFER_FULL</code>. When
choosing log buffer and file sizes for in-memory logs, applications
should ensure the in-memory log buffer size is large enough that no
transaction will ever span the entire buffer, and avoid a state where
the in-memory buffer is full and no space can be freed because a
transaction that started in the first log "file" is still active.
</p>
<p>
Calling <code class="methodname">DbEnv::log_set_config()</code> with the
<code class="literal">DB_LOG_IN_MEMORY</code> flag
affects the database environment, including all threads of control
accessing the database environment.
</p>
<p>
The <code class="literal">DB_LOG_IN_MEMORY</code> flag may be used to configure Berkeley DB only
before the <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a>
method is called.
</p>
</li>
<li>
<p>
<code class="literal">DB_LOG_ZERO</code>
</p>
<p>
If set, zero all pages of a log file when that log file is created.
This has shown to provide greater transaction throughput in some
environments. The log file will be zeroed by the thread which needs to
re-create the new log file. Other threads may not write to the log
file while this is happening.
</p>
<p>
Calling <code class="methodname">DbEnv::log_set_config()</code> with the
<code class="literal">DB_LOG_ZERO</code> flag affects only the current environment handle.
</p>
<p>
The <code class="literal">DB_LOG_ZERO</code> flag may be used to configure Berkeley DB at any time.
</p>
</li>
</ul>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp8392312"></a>onoff</h4>
</div>
</div>
</div>
<p>
If the <span class="bold"><strong>onoff</strong></span> parameter is zero, the
specified flags are cleared; otherwise they are set.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp8357144"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">DbEnv::log_set_config()</code> <span>
<span>
method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a>
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors:
</span>
</span>
</p>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp8390600"></a>EINVAL</h4>
</div>
</div>
</div>
<p>
An invalid flag value or parameter was specified.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp8396880"></a>Class</h3>
</div>
</div>
</div>
<p>
<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a>
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp8393856"></a>See Also</h3>
</div>
</div>
</div>
<p>
<a class="xref" href="lsn.html#loglist" title="Logging Subsystem and Related Methods">Logging Subsystem and Related Methods</a>
</p>
</div>
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