Sindbad~EG File Manager
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<div class="sect1" lang="en" xml:lang="en">
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<h2 class="title" style="clear: both"><a id="envlog_set_config"></a>
<span>DbEnv::log_set_config()</span>
</h2>
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<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="idm139755613080288"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idm139755613065904"></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_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_BLOB"></a>
<code class="literal">DB_LOG_EXT_FILE</code>
</p>
<p>
Enables full logging of
<a class="link" href="blob.html" title="Chapter 14. External Files">external file</a> data. Only
use this flag if using replication or running a hot
backup; otherwise, it will impose a performance
penalty on external file operations.
</p>
<p>
This flag is off by default, unless Replication is
enabled for the environment. In that case, it is
on by default.
</p>
<p>
The <code class="literal">DB_LOG_EXT_FILE</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_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_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()">
<span>DbEnv::open()</span>
</a>
method is called.
</p>
</li>
<li>
<p><a id="log_set_config_DB_LOG_NOSYNC"></a>
<code class="literal">DB_LOG_NOSYNC</code>
</p>
<p>
If set, the transaction log is not flushed from the
operating system cache to stable storage when a
transaction commits or the logging system switches
log files. This can further increase performance
when all of the applications in an environment use
less-than-durable transactions (DB_TXN_NOSYNC and
DB_TXN_WRITE_NOSYNC).
</p>
<p>
Turning on <code class="literal">DB_LOG_NOSYNC</code> removes
the durability guarantee of current or future
DB_TXN_SYNC transactions, as well as any
transactions which have been active since the last
checkpoint. All database files must be verified
and/or restored from a replication group master or
archival backup after system failure.
</p>
<p>
Turning off <code class="literal">DB_LOG_NOSYNC</code> may be
done at any time. Current and future DB
DB_TXN_SYNC transactions will return to full ACID
characteristics once a checkpoint or log file
switch occurs.
</p>
<p>
Calling
<code class="methodname">DbEnv::log_set_config()</code>
with the <code class="literal">DB_LOG_NOSYNC</code> flag
affects the database environment, including all
threads of control accessing the database
environment.
</p>
<p>
The <code class="literal">DB_LOG_NOSYNC</code> flag may be
used to configure Berkeley DB at any time.
<a class="xref" href="envopen.html" title="DbEnv::open()">
<span>DbEnv::open()</span>
</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="idm139755613065776"></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="idm139755613077776"></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="idm139755613038224"></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="idm139755613036080"></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="idm139755613022560"></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>
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