title: syslog-ng flush_lines option does not work
body: <p>I use syslog-ng 3.5.3 on ubuntu 14.04
  I need to reduce system load.
  So I would like to use flush_lines option.</p>
  
  <p>I added flush_lines(2) to global options.
  I confirm the behavior in terminal with <code>tail -h /var/log/messages</code></p>
  
  <p>But log messages was written immediately as before.
  How can I out put some messages at once? </p>
  
  <p>I use the config below for syslog-ng.</p>
  
  <pre><code>@version: 3.5
  @include "scl.conf"
  @include "`scl-root`/system/tty10.conf"
  
  # Syslog-ng configuration file, compatible with default Debian syslogd
  # installation.
  
  # First, set some global options.
  options { chain_hostnames(off); flush_lines(2); use_dns(no); use_fqdn(no);
        owner("root"); group("adm"); perm(0640); stats_freq(0);
        bad_hostname("^gconfd$");
  };
  
  ########################
  # Sources
  ########################
  # This is the default behavior of sysklogd package
  # Logs may come from unix stream, but not from another machine.
  #
  source s_src {
         system();
         internal();
  };
  
  # If you wish to get logs from remote machine you should uncomment
  # this and comment the above source line.
  #
  #source s_net { tcp(ip(127.0.0.1) port(1000)); };
  
  ########################
  # Destinations
  ########################
  # First some standard logfile
  #
  destination d_auth { file("/var/log/auth.log"); };
  destination d_cron { file("/var/log/cron.log"); };
  destination d_daemon { file("/var/log/daemon.log"); };
  destination d_kern { file("/var/log/kern.log"); };
  destination d_lpr { file("/var/log/lpr.log"); };
  destination d_mail { file("/var/log/mail.log"); };
  destination d_syslog { file("/var/log/syslog"); };
  destination d_user { file("/var/log/user.log"); };
  destination d_uucp { file("/var/log/uucp.log"); };
  
  # This files are the log come from the mail subsystem.
  #
  destination d_mailinfo { file("/var/log/mail.info"); };
  destination d_mailwarn { file("/var/log/mail.warn"); };
  destination d_mailerr { file("/var/log/mail.err"); };
  
  # Logging for INN news system
  #
  destination d_newscrit { file("/var/log/news/news.crit"); };
  destination d_newserr { file("/var/log/news/news.err"); };
  destination d_newsnotice { file("/var/log/news/news.notice"); };
  
  # Some `catch-all' logfiles.
  #
  destination d_debug { file("/var/log/debug"); };
  destination d_error { file("/var/log/error"); };
  destination d_messages { file("/var/log/messages"); };
  
  # The root's console.
  #
  destination d_console { usertty("root"); };
  
  # Virtual console.
  #
  destination d_console_all { file(`tty10`); };
  
  # The named pipe /dev/xconsole is for the nsole' utility.  To use it,
  # you must invoke nsole' with the -file' option:
  #
  #    $ xconsole -file /dev/xconsole [...]
  #
  destination d_xconsole { pipe("/dev/xconsole"); };
  
  # Send the messages to an other host
  #
  #destination d_net { tcp("127.0.0.1" port(1000) log_fifo_size(1000)); };
  
  # Debian only
  destination d_ppp { file("/var/log/ppp.log"); };
  
  ########################
  # Filters
  ########################
  # Here's come the filter options. With this rules, we can set which 
  # message go where.
  
  filter f_dbg { level(debug); };
  filter f_info { level(info); };
  filter f_notice { level(notice); };
  filter f_warn { level(warn); };
  filter f_err { level(err); };
  filter f_crit { level(crit .. emerg); };
  
  filter f_debug { level(debug) and not facility(auth, authpriv, news, mail); };
  filter f_error { level(err .. emerg) ; };
  filter f_messages { level(info,notice,warn) and 
                      not facility(auth,authpriv,cron,daemon,mail,news); };
  
  filter f_auth { facility(auth, authpriv) and not filter(f_debug); };
  filter f_cron { facility(cron) and not filter(f_debug); };
  filter f_daemon { facility(daemon) and not filter(f_debug); };
  filter f_kern { facility(kern) and not filter(f_debug); };
  filter f_lpr { facility(lpr) and not filter(f_debug); };
  filter f_local { facility(local0, local1, local3, local4, local5,
                          local6, local7) and not filter(f_debug); };
  filter f_mail { facility(mail) and not filter(f_debug); };
  filter f_news { facility(news) and not filter(f_debug); };
  filter f_syslog3 { not facility(auth, authpriv, mail) and not filter(f_debug); };
  filter f_user { facility(user) and not filter(f_debug); };
  filter f_uucp { facility(uucp) and not filter(f_debug); };
  
  filter f_cnews { level(notice, err, crit) and facility(news); };
  filter f_cother { level(debug, info, notice, warn) or facility(daemon, mail); };
  
  filter f_ppp { facility(local2) and not filter(f_debug); };
  filter f_console { level(warn .. emerg); };
  
  ########################
  # Log paths
  ########################
  log { source(s_src); filter(f_auth); destination(d_auth); };
  log { source(s_src); filter(f_cron); destination(d_cron); };
  log { source(s_src); filter(f_daemon); destination(d_daemon); };
  log { source(s_src); filter(f_kern); destination(d_kern); };
  log { source(s_src); filter(f_lpr); destination(d_lpr); };
  log { source(s_src); filter(f_syslog3); destination(d_syslog); };
  log { source(s_src); filter(f_user); destination(d_user); };
  log { source(s_src); filter(f_uucp); destination(d_uucp); };
  
  log { source(s_src); filter(f_mail); destination(d_mail); };
  #log { source(s_src); filter(f_mail); filter(f_info); destination(d_mailinfo); };
  #log { source(s_src); filter(f_mail); filter(f_warn); destination(d_mailwarn); };
  #log { source(s_src); filter(f_mail); filter(f_err); destination(d_mailerr); };
  
  log { source(s_src); filter(f_news); filter(f_crit); destination(d_newscrit); };
  log { source(s_src); filter(f_news); filter(f_err); destination(d_newserr); };
  log { source(s_src); filter(f_news); filter(f_notice); destination(d_newsnotice); };
  #log { source(s_src); filter(f_cnews); destination(d_console_all); };
  #log { source(s_src); filter(f_cother); destination(d_console_all); };
  
  #log { source(s_src); filter(f_ppp); destination(d_ppp); };
  
  log { source(s_src); filter(f_debug); destination(d_debug); };
  log { source(s_src); filter(f_error); destination(d_error); };
  log { source(s_src); filter(f_messages); destination(d_messages); };
  
  log { source(s_src); filter(f_console); destination(d_console_all);
                      destination(d_xconsole); };
  log { source(s_src); filter(f_crit); destination(d_console); };
  
  # All messages send to a remote site
  #
  #log { source(s_src); destination(d_net); };
  
  ###
  # Include all config files in /etc/syslog-ng/conf.d/
  ###
  @include "/etc/syslog-ng/conf.d/*.conf"
  </code></pre>