logging_collector

doc html

<p>
         This parameter enables the <em class="firstterm">logging collector</em>, which
         is a background process that captures log messages
         sent to <span class="systemitem">stderr</span> and redirects them into log files.
         This approach is often more useful than
         logging to <span class="application">syslog</span>, since some types of messages
         might not appear in <span class="application">syslog</span> output.  (One common
         example is dynamic-linker failure messages; another is error messages
         produced by scripts such as <code class="varname">archive_command</code>.)
         This parameter can only be set at server start.
       </p><div class="note"><h3 class="title">Note</h3><p>
         It is possible to log to <span class="systemitem">stderr</span> without using the
         logging collector; the log messages will just go to wherever the
         server's <span class="systemitem">stderr</span> is directed.  However, that method is
         only suitable for low log volumes, since it provides no convenient
         way to rotate log files.  Also, on some platforms not using the
         logging collector can result in lost or garbled log output, because
         multiple processes writing concurrently to the same log file can
         overwrite each other's output.
        </p></div><div class="note"><h3 class="title">Note</h3><p>
          The logging collector is designed to avoid dropping messages.  This means
          that in case of extremely high load, server processes could be
          blocked while trying to send additional log messages when the
          collector has fallen behind.  In contrast, <span class="application">syslog</span>
          prefers to drop messages if it cannot write them, which means it
          may fail to log some messages in such cases but it will not block
          the rest of the system.
        </p><p>
         The logging collector does not guarantee that log messages have
         reached durable storage.  It can still lose messages due to a system
         crash, power loss, or an error while writing the log file.
        </p></div>

documentation revision

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