mod_proxy_fcgi.xml: add a note about connection reuse

    </highlight>

    </example>

    <note><title>Enable connection reuse to a FCGI backend like PHP-FPM</title>

    <p>Please keep in mind that PHP-FPM (at the time of writing, February 2018)

    uses a prefork model, namely each of its worker processes can handle one

    connection at the time.<br /> 

    By default mod_proxy (configured with <code>enablereuse=on</code>)

    allows a connection pool of

    <directive module="mpm_common">ThreadsPerChild</directive> connections to the

    backend for each httpd process, so the following use cases should be taken

    into account:</p>

    <ul>

      <li>Under HTTP/1.1 load it will likely cause the creation of up to

      <directive module="mpm_common">MaxRequestWorkers</directive>

      connections to the FCGI backend.</li>

      <li>Under HTTP/2 load, due to how <module>mod_http2</module> is implemented,

      there are additional h2 worker threads that may force the creation of other

      backend connections. The overall count of connections in the pools may raise

      to more than <directive module="mpm_common">MaxRequestWorkers</directive>.</li>

    </ul>

    <p>The maximum number of PHP-FPM worker processes needs to be configured wisely,

    since there is the chance that they will all end up "busy" handling idle

    persistent connections, without any room for new ones to be established,

    and the end user experience will be a pile of HTTP request timeouts.</p>

    </note>

    <p> The following example passes the request URI as a filesystem

    path for the PHP-FPM daemon to run. The request URL is implicitly added

    to the 2nd parameter. The hostname and port following fcgi:// are where