2.4.x/docs/manual/mod/mod_logio.xml

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<modulesynopsis metafile="mod_logio.xml.meta">

<name>mod_logio</name>
<description>Logging of input and output bytes per request</description>
<status>Extension</status>
<sourcefile>mod_logio.c</sourcefile>
<identifier>logio_module</identifier>

<summary>

    <p>This module provides the logging of input and output number of
    bytes received/sent per request. The numbers reflect the actual bytes
    as received on the network, which then takes into account the
    headers and bodies of requests and responses. The counting is done
    before SSL/TLS on input and after SSL/TLS on output, so the numbers
    will correctly reflect any changes made by encryption.</p>

    <p>This module requires <module>mod_log_config</module>.</p>

    <note>When KeepAlive connections are used with SSL, the overhead of the SSL
    handshake is reflected in the byte count of the first request on the
    connection.  When per-directory SSL renegotiation occurs, the bytes are associated
    with the request that triggered the renegotiation.</note>

</summary>

<seealso><module>mod_log_config</module></seealso>
<seealso><a href="../logs.html">Apache Log Files</a></seealso>

<section id="formats">
<title>Custom Log Formats</title>

    <p>This module adds three new logging directives. The characteristics of the
    request itself are logged by placing "<code>%</code>" directives in
    the format string, which are replaced in the log file by the values as
    follows:</p>

    <table border="1" style="zebra">
    <tr><th>Format&nbsp;String</th>
        <th>Description</th></tr>

    <tr><td><code>%I</code></td>
        <td>Bytes received, including request and headers, cannot be
        zero.</td></tr>

    <tr><td><code>%O</code></td>
        <td>Bytes sent, including headers, cannot be zero.</td></tr>

    <tr><td><code>%S</code></td>
        <td>Bytes transferred (received and sent), including request and headers,
        cannot be zero. This is the combination of %I and %O.<br />
        Available in Apache 2.4.7 and later</td></tr>

    <tr><td><code>%^FB</code></td>
        <td>Delay in microseconds between when the request arrived and the
        first byte of the response headers are written.  Only available if 
        <directive>LogIOTrackTTFB</directive> is set to ON.<br />
        Available in Apache 2.4.13 and later</td></tr>
    </table>

    <p>Usually, the functionality is used like this:</p>

    <dl>
      <dt>Combined I/O log format:</dt>
      <dd><code>"%h %l %u %t \"%r\" %&gt;s %b \"%{Referer}i\"
      \"%{User-agent}i\" %I %O"</code></dd>
    </dl>
</section>

<directivesynopsis>
<name>LogIOTrackTTFB</name>
<description>Enable tracking of time to first byte (TTFB)</description>
<syntax>LogIOTrackTTFB ON|OFF</syntax>
<default>LogIOTrackTTFB OFF</default>
<contextlist><context>server config</context><context>virtual host</context>
<context>directory</context><context>.htaccess</context></contextlist>
<override>none</override>
<compatibility>Apache HTTP Server 2.4.13 and later</compatibility>

<usage>
    <p>This directive configures whether this module tracks the delay
    between the request being read and the first byte of the response
    headers being written.  The resulting value may be logged with the 
    <code>%^FB</code> format.</p>
</usage>
</directivesynopsis>

</modulesynopsis>