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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>DbEnv::log_set_config()</title>
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Berkeley DB C++ API Reference" />
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<link rel="up" href="lsn.html" title="Chapter 8. The DbLsn Handle" />
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<link rel="prev" href="logput.html" title="DbEnv::log_put()" />
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<div xmlns="" class="navheader">
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<p>Library Version 11.2.5.2</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">DbEnv::log_set_config()</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="logput.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 8.
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The DbLsn Handle
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="logstat.html">Next</a></td>
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</tr>
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</table>
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<hr />
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="envlog_set_config"></a>DbEnv::log_set_config()</h2>
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</div>
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</div>
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</div>
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<pre class="programlisting">#include <db_cxx.h>
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int
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DbEnv::log_set_config(u_int32_t flags, int onoff); </pre>
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<p>
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The <code class="methodname">DbEnv::log_set_config()</code> method configures the Berkeley DB
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logging subsystem.
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</p>
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<p>
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The <code class="methodname">DbEnv::log_set_config()</code> method configures a database
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environment, not only operations performed using the specified
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<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> handle.
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</p>
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<p>
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The <code class="methodname">DbEnv::log_set_config()</code> method may be called at any time during
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the life of the application.
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</p>
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<p>
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The <code class="methodname">DbEnv::log_set_config()</code> <span>
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<span>
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method either returns a non-zero error value or throws an
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exception that encapsulates a non-zero error value on
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failure, and returns 0 on success.
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</span>
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</span>
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</p>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3638998"></a>Parameters</h3>
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</div>
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</div>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3639436"></a>flags</h4>
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</div>
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</div>
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</div>
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<p>
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The <span class="bold"><strong>flags</strong></span> parameter must be set by
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bitwise inclusively <span class="bold"><strong>OR</strong></span>'ing together
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one or more of the following values:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p><a id="log_set_config_DB_LOG_DIRECT"></a>
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<code class="literal">DB_LOG_DIRECT</code>
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</p>
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<p>
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Turn off system buffering of Berkeley DB log files to avoid double
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caching.
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</p>
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<p>
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Calling <code class="methodname">DbEnv::log_set_config()</code> with the DB_LOG_DIRECT flag only
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affects the specified <a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> handle (and any other
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Berkeley DB handles opened within the scope of that handle). For
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consistent behavior across the environment, all
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<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> handles opened in the
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environment must either set the DB_LOG_DIRECT flag or the flag should
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be specified in the <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> configuration file.
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</p>
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<p>
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The <code class="literal">DB_LOG_DIRECT</code> flag may be used to configure Berkeley DB at any
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time during the life of the application.
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</p>
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</li>
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<li>
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<p><a id="log_set_config_DB_LOG_DSYNC"></a>
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<code class="literal">DB_LOG_DSYNC</code>
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</p>
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<p>
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Configure Berkeley DB to flush log writes to the backing disk before
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returning from the write system call, rather than flushing log writes
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explicitly in a separate system call, as necessary. This is only
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available on some systems (for example, systems supporting the
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IEEE/ANSI Std 1003.1 (POSIX) standard O_DSYNC flag, or systems
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supporting the Windows FILE_FLAG_WRITE_THROUGH flag). This flag may
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result in inaccurate file modification times and other file-level
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information for Berkeley DB log files. This flag may offer a
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performance increase on some systems and a performance decrease on
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others.
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</p>
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<p>
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Calling <code class="methodname">DbEnv::log_set_config()</code> with the DB_LOG_DSYNC flag only
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affects the specified <a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> handle (and any other
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Berkeley DB handles opened within the scope of that handle). For
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consistent behavior across the environment, all
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<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a> handles opened in the
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environment must either set the DB_LOG_DSYNC flag or the flag should
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be specified in the <a href="../../programmer_reference/env_db_config.html#env_db_config.DB_CONFIG" class="olink">DB_CONFIG</a> configuration file.
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</p>
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<p>
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The <code class="literal">DB_LOG_DSYNC</code> flag may be used to configure Berkeley DB at any time
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during the life of the application.
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</p>
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</li>
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<li>
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<p><a id="log_set_config_DB_LOG_AUTO_REMOVE"></a>
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<code class="literal">DB_LOG_AUTO_REMOVE</code>
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</p>
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<p>
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If set, Berkeley DB will automatically remove log files that are no
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longer needed.
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</p>
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<p>
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Automatic log file removal is likely to make catastrophic recovery
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impossible.
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</p>
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<p>
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Replication Manager applications operate in a
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group-aware manner for log file removal, and automatic log
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file removal simplifies the application.
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</p>
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<p>
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Replication Base API applications will rarely want to configure automatic log
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file removal as it increases the likelihood a master will be unable to
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satisfy a client's request for a recent log record.
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</p>
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<p>
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Calling <code class="methodname">DbEnv::log_set_config()</code> with the
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<code class="literal">DB_LOG_AUTO_REMOVE</code> flag
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affects the database environment, including all threads of control
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accessing the database environment.
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</p>
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<p>
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The <code class="literal">DB_LOG_AUTO_REMOVE</code> flag may be used to configure Berkeley DB at
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any time during the life of the application.
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</p>
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</li>
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<li>
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<p><a id="log_set_config_DB_LOG_IN_MEMORY"></a>
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<code class="literal">DB_LOG_IN_MEMORY</code>
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</p>
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<p>
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If set, maintain transaction logs in memory rather than on disk. This
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means that transactions exhibit the ACI (atomicity, consistency, and
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isolation) properties, but not D (durability); that is, database
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integrity will be maintained, but if the application or system fails,
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integrity will not persist. All database files must be verified
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and/or restored from a replication group master or archival backup
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after application or system failure.
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</p>
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<p>
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When in-memory logs are configured and no more log buffer space is
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available, Berkeley DB methods may return an additional error value,
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<code class="literal">DB_LOG_BUFFER_FULL</code>. When
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choosing log buffer and file sizes for in-memory logs, applications
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should ensure the in-memory log buffer size is large enough that no
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transaction will ever span the entire buffer, and avoid a state where
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the in-memory buffer is full and no space can be freed because a
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transaction that started in the first log "file" is still active.
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</p>
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<p>
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Calling <code class="methodname">DbEnv::log_set_config()</code> with the
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<code class="literal">DB_LOG_IN_MEMORY</code> flag
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affects the database environment, including all threads of control
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accessing the database environment.
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</p>
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<p>
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The <code class="literal">DB_LOG_IN_MEMORY</code> flag may be used to configure Berkeley DB only
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before the <a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a>
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method is called.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">DB_LOG_ZERO</code>
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</p>
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<p>
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If set, zero all pages of a log file when that log file is created.
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This has shown to provide greater transaction throughput in some
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environments. The log file will be zeroed by the thread which needs to
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re-create the new log file. Other threads may not write to the log
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file while this is happening.
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</p>
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<p>
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Calling <code class="methodname">DbEnv::log_set_config()</code> with the
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<code class="literal">DB_LOG_ZERO</code> flag affects only the current environment handle.
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</p>
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<p>
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The <code class="literal">DB_LOG_ZERO</code> flag may be used to configure Berkeley DB at any time.
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</p>
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</li>
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</ul>
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</div>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3639662"></a>onoff</h4>
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</div>
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</div>
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</div>
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<p>
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If the <span class="bold"><strong>onoff</strong></span> parameter is zero, the
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specified flags are cleared; otherwise they are set.
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</p>
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</div>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3639078"></a>Errors</h3>
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</div>
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</div>
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</div>
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<p>
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The <code class="methodname">DbEnv::log_set_config()</code> <span>
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<span>
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method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a>
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exception, encapsulating one of the following non-zero errors, or return one
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of the following non-zero errors:
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</span>
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</span>
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</p>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="id3639633"></a>EINVAL</h4>
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</div>
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</div>
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</div>
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<p>
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An invalid flag value or parameter was specified.
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</p>
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</div>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3638999"></a>Class</h3>
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</div>
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</div>
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</div>
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<p>
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<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a>
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</p>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="id3639272"></a>See Also</h3>
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</div>
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</div>
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</div>
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<p>
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<a class="xref" href="lsn.html#loglist" title="Logging Subsystem and Related Methods">Logging Subsystem and Related Methods</a>
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</p>
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</div>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="logput.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="lsn.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="logstat.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">DbEnv::log_put() </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> DbEnv::log_stat()</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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