Emacs

Emacs Feed The pages where I write about Emacs. It doesn’t happen very often. I think you’re probably best off following Planet Emacsen.

2015-06-24 Emacs Live

I’ve been trying to switch from my own Emacs setup to Emacs Live. Some things are great. Some things… I don’t know. They need a lot of getting used to.

I’ve created my own pack in ~/elisp/alex-pack.

In ~/.emacs-live.el:

(live-add-packs '(~/elisp/alex-pack))

Paredit is messing with how I navigate using Control + Arrow Keys.

In my own pack, ~/elisp/alex-pack/init.el:

(dolist (x '(scheme emacs-lisp lisp clojure))
  (let ((hook (intern (concat (symbol-name x) "-mode-hook"))))
    (set hook (delq 'enable-paredit-mode (symbol-value hook)))))

Delete Trailing Whitespace Mode deleted some non-breaking spaces in my SVG document. This may be an indication that I should write better SVG.

In my own pack, ~/elisp/alex-pack/init.el:

(setq before-save-hook
      (delq 'live-clenup-whitespace before-save-hook))

Changing how C-h works. Help is now on M-h. I’ll adapt. Except I’ve found modes where M-h does describe-mode and that confuses me. I think I’m going to stop using the bindings pack provided by Emacs Live.

In ~/.emacs-live.el:

(setq live-packs (delete "stable/bindings-pack" live-packs))

Ispell no longer shows any content in the *Choices* buffer/window. What’s up?

I have trouble accessing the file open history using <up> or M-p. Similarly, I can’t edit the filename using <left> or <right>. What’s up? I think I’m going to disable Ido mode for find-file.

In my own pack, ~/elisp/alex-pack/init.el:

(ido-mode 'buffers)

I like the some of the fontification, but it turns out that I’m starting to confuse the Emacs frame with terminal windows. So I think I’m going to stop using the colour pack provided by Emacs Live.

In ~/.emacs-live.el:

(setq live-packs (delete "stable/colour-pack" live-packs))

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2015-06-11 AKICK on the Emacs Channel

Here’s how to define two commands to use ChanServ’s AKICK command on Freenode. The commented commands are what I had before. The benefit of the AKICK command is the timeout.

;; rcirc /kickban

(eval-after-load 'rcirc
  '(defun-rcirc-command kickban (input)
     "Kickban a nick for two hours."
     (interactive "s")
     ;; (rcirc-send-string process (format "MODE %s +b %s!*@*" target input))
     ;; (rcirc-send-string process (format "KICK %s %s kickban!" target input))
     (rcirc-send-privmsg process "chanserv" (format "AKICK %s ADD %s !T 120 banned for 2h -- kensanata" target input))))

;; rcirc /unban

(eval-after-load 'rcirc
  '(defun-rcirc-command unban (input)
     "Unban a nick."
     (interactive "s")
     ;; (rcirc-send-string process (format "MODE %s -b %s!*@*" target input))
     (rcirc-send-privmsg process "chanserv" (format "AKICK %s DEL %s!*@*" target input))))

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2014-12-30 Emac Wiki Migration

OK, I guess Nic and I have a plan. We’ve started writing a backlog for the Emacs Wiki Migration. Hopefully this will make the current wiki easier to cache.

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2014-12-28 Emacs Wiki Migration

Gaah! :(

So, I still think this is a problem with the hosting provider. Here’s what I think is evidence:

https://farm8.staticflickr.com/7575/15509223034_8ee49a110d_o.png

What could be causing this regular forks if not other virtual machines hogging CPU at regular intervals, or other virtual machines hogging disk access, causing CGI scripts to pile up? I wonder…

Things I care about: Diagnosing Disk I/O issues: swapping, high IO wait, congestion.

Let’s see what iotop -ao says right now:

Total DISK READ:       0.00 B/s | Total DISK WRITE:       0.00 B/s
  TID  PRIO  USER     DISK READ  DISK WRITE  SWAPIN     IO>    COMMAND                                                                                    
11774 be/4 www-data     36.00 K     20.00 K  0.00 %  0.02 % [/usr/sbin/apach]
11801 be/4 www-data      0.00 B     12.00 K  0.00 %  0.00 % apache2 -k start
11810 be/4 www-data      0.00 B      4.00 K  0.00 %  0.00 % apache2 -k start 
29022 be/4 root          0.00 B     32.00 K  0.00 %  0.00 % monit -c /etc/monit/monitrc
20368 be/4 root          0.00 B     60.00 K  0.00 %  0.00 % rsyslogd -c5

I don’t think we’re using swap at all (munin shows us using less than 2G with 4G available). But who knows? I used top, pressed f to show the list of fields, and I used d (display) and s (sort) on SWAP.

top - 22:14:00 up 7 days, 21:11,  2 users,  load average: 0.51, 0.31, 0.22
Tasks:  24 total,   1 running,  23 sleeping,   0 stopped,   0 zombie
%Cpu(s):  3.6 us,  0.6 sy,  0.0 ni, 95.8 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem:   4194304 total,   894976 used,  3299328 free,        0 buffers
KiB Swap:  1048576 total,     5524 used,  1043052 free,   785880 cached

  PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+  COMMAND              SWAP 
15874 root      20   0 71192 5224 1620 S   0.0  0.1   2:11.36 fail2ban-server      2296 
27076 root      20   0 72564 1092  708 S   0.0  0.0   0:16.47 sendmail-mta         1384 
21949 root      20   0 49892  684  568 S   0.0  0.0   0:02.23 sshd                  492 
29022 root      20   0 42984 2688 2136 S   0.0  0.1   0:48.28 monit                 284 
20367 root      20   0 49860 4504  712 S   0.0  0.1   0:24.56 rsyslogd              236 
19427 root      30  10 12252  788  784 S   0.0  0.0   0:00.00 rsync                 160 
15876 root      20   0 22260  896  672 S   0.0  0.0   0:08.86 gam_server            136 
22815 root      20   0 20368  496  364 S   0.0  0.0   0:02.03 cron                  120 

I don’t think that’s suspicious. Those tasks probably ended up in swap because they have been running for so long?

I installed the apache_vhosts plugin for munin. I think there will be no surprises with emacswiki.org taking the brunt with a factor of 10:1. Right now, however, it seems to be misconfigured somehow, not recording any emacswiki.org traffic and missing most of the other traffic. Weird!

Ah, apache_vhosts munin plugin problem fixed. All my sites were using a CustomLog except for alexschroeder.ch:80 and campaignwiki.org:80—these just redirect to the HTTPS version of the site. Thus, these sites were being counted by the apache_vhosts plugin. But that is now fixed, and we have a graph!

https://farm8.staticflickr.com/7527/15960447830_a102ae6df7_o.png

https://farm9.staticflickr.com/8667/15528022193_78df3fc37d_o.png

I’m not quite sure how to compare this with the following log file analysis where I simply group access by site:

root@kallobombus:/var/log/apache2# perl /home/alex/bin/site-comparison < access.log
                          Site       hits bandw. hits% interv. status code distrib.
             www.emacswiki.org     104499     6K  47%    2.1s  301 (29%), 501 (26%), 200 (21%
          www.alexschroeder.ch      67396    31K  30%    3.2s  200 (94%), 304 (2%), 301 (1%),
         www.communitywiki.org      24574    17K  11%    8.9s  200 (80%), 301 (7%), 404 (3%),
          www.campaignwiki.org      13902    13K   6%   15.6s  200 (74%), 404 (17%), 302 (4%)
               www.oddmuse.org       9498    23K   4%   22.9s  200 (66%), 404 (14%), 301 (12%
       www.arabisch-lernen.org        845     7K   0%  256.4s  200 (94%), 404 (3%), 403 (1%),
         www.orientalisch.info        404     4K   0%  536.5s  200 (80%), 301 (14%), 404 (2%)

Ah, of course. The access.log is can be up to seven days. Thus:

root@kallobombus:/var/log/apache2# tail -n 10000 access.log | /home/alex/bin/site-comparison 
                          Site       hits bandw. hits% interv. status code distrib.
          www.alexschroeder.ch       6430    24K  64%    1.9s  200 (88%), 301 (8%), 404 (1%),
             www.emacswiki.org       1187    12K  11%   10.4s  301 (38%), 200 (36%), 404 (19%
         www.communitywiki.org       1150    14K  11%   10.7s  200 (79%), 301 (7%), 404 (5%),
          www.campaignwiki.org        604     9K   6%   20.3s  200 (58%), 301 (22%), 404 (12%
               www.oddmuse.org        415    18K   4%   29.6s  200 (64%), 404 (18%), 301 (10%
       www.arabisch-lernen.org        202     5K   2%   37.4s  404 (90%), 200 (9%), 501 (0%)
         www.orientalisch.info         12     4K   0% 1010.2s  200 (91%), 304 (8%)

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2014-12-27 Emacs Wiki Migration

Based on some information I got from Charlie McMackin—who had set up a virtual machine and got Emacs Wiki to run on it—I switched Apache from “worker” to “prefork” and I’m now using the following config:

<IfModule mpm_prefork_module>
    StartServers          2
    MinSpareServers       1
    MaxSpareServers       2
    MaxClients		  5
    MaxRequestsPerChild 10000
</IfModule>

I checked http://localhost/server-info and can confirm that we’re running Prefork:

Server Settings

Server Version: Apache/2.2.22 (Debian) mod_ssl/2.2.22 OpenSSL/1.0.1e mod_perl/
    2.0.7 Perl/v5.14.2
Server Built: Jul 24 2014 15:34:00
Server loaded APR Version: 1.4.6
Compiled with APR Version: 1.4.6
Server loaded APU Version: 1.4.1
Compiled with APU Version: 1.4.1
Module Magic Number: 20051115:30
Hostname/port: alexschroeder.ch:443
Timeouts: connection: 300    keep-alive: 5
MPM Name: Prefork
MPM Information: Max Daemons: 5 Threaded: no Forked: yes
Server Architecture: 64-bit

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2014-12-26 Emacs Wiki Migration

I’m not happy. Today, multiple Apache restarts. Grepping syslog for restarts:

Dec 26 07:38:32 localhost monit[29022]: 'apache' trying to restart
Dec 26 11:38:53 localhost monit[29022]: 'apache' trying to restart
Dec 26 14:47:16 localhost monit[29022]: 'apache' trying to restart
Dec 26 16:49:46 localhost monit[29022]: 'apache' trying to restart
Dec 26 17:26:06 localhost monit[29022]: 'apache' trying to restart
Dec 26 18:06:29 localhost monit[29022]: 'apache' trying to restart
Dec 26 19:48:54 localhost monit[29022]: 'apache' trying to restart

https://farm8.staticflickr.com/7566/15494392223_95ee7bf147_o.png

I’m going to further reduce the number of threads.

<IfModule mpm_worker_module>
    StartServers          1
    ServerLimit           2
    ThreadsPerChild       5
    MaxClients           10
    MinSpareThreads      10
    MaxSpareThreads      20
    MaxRequestsPerChild  10000
</IfModule>

I also installed lsof and wrote a little plugin for munin. What I really want to see is the number of open files, or something like that. I remember checking that when we had load problems on Mirabel without a matching number of processes actually doing anything. Just in case the processes are all waiting for file access.

I’m not sure how well this is going to work, but this is my first stab at the files plugin. 😊

#!/bin/sh
# 
# Plugin to monitor the number of open files in the system.
#
# Parameters:
# 	
# 	config   (required)
# 	autoconf (optional - used by munin-config)
#
# Magic markers (Used by munin-config and some installation scripts.
# Optional):
#
#%# family=contrib
#%# capabilities=autoconf

# PROC=${0##*/files_}
PORTS="80 443"

if [ "$1" = "autoconf" ]; then
	if [ -x /usr/bin/lsof ]; then
		echo yes
		exit 0
	else
		echo "no (no lsof)"
		exit 0
	fi
fi

if [ "$1" = "config" ]; then
	echo graph_title "open files"
	echo graph_vlabel "number of files"
	echo graph_info "This graph shows the number of open files by port (80 is http, 443 is https)."
	echo graph_category "apache"
	for P in $PORTS; do
	    echo "$P.label port $P"
	done
	exit 0
fi

for P in $PORTS; do 
    N=$(lsof -i :$P | tail -n +2 | wc -l)
    echo "$P.value $N"
done

All I know is that load is climbing right now. Close to 6. Time for bed! Grrrrr.

A few hours later, stats seem to be worse:

Dec 26 22:47:16 localhost monit[29022]: 'apache' trying to restart
Dec 26 23:23:34 localhost monit[29022]: 'apache' trying to restart
Dec 26 23:58:01 localhost monit[29022]: 'apache' trying to restart
Dec 27 00:10:19 localhost monit[29022]: 'apache' trying to restart
Dec 27 00:38:40 localhost monit[29022]: 'apache' trying to restart
Dec 27 01:06:58 localhost monit[29022]: 'apache' trying to restart
Dec 27 01:17:15 localhost monit[29022]: 'apache' trying to restart
Dec 27 03:51:40 localhost monit[29022]: 'apache' trying to restart
Dec 27 04:23:59 localhost monit[29022]: 'apache' trying to restart
Dec 27 04:42:21 localhost monit[29022]: 'apache' trying to restart
Dec 27 05:30:47 localhost monit[29022]: 'apache' trying to restart
Dec 27 06:59:09 localhost monit[29022]: 'apache' trying to restart
Dec 27 08:05:33 localhost monit[29022]: 'apache' trying to restart

Let’s hope that things will improve with prefork!

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2014-12-25 Emacs Wiki Migration

I’ve been thinking about special-casing some caching: a mod_rewrite rule that says:

  • if the URL has the form /emacs/page
  • and there is no cookie (ie. bots, just readers)
  • and there is an if-none-match header (from nginx, I presume?)
  • and its value matches the “default”
  • return 304 without invoking the wiki

So, what’s the “default”?

sub DoBrowseRequest {
  ...
  print $q->header(-status=>'304 NOT MODIFIED') and return if PageFresh(); # return value is ignored
  ...
}

sub PageFresh { # pages can depend on other pages (ie. last update), admin status, and css
  return 1 if $q->http('HTTP_IF_NONE_MATCH') and GetParam('cache', $UseCache) >= 2
    and $q->http('HTTP_IF_NONE_MATCH') eq PageEtag();
}

sub PageEtag {
  my ($changed, $visible, %params) = CookieData();
  return UrlEncode(join($FS, $LastUpdate||$Now, sort(values %params))); # no CTL in field values
}

And what about $LastUpdate?

  my $ts = (stat($IndexFile))[9]; # always stat for multiple server processes
  ...
  $LastUpdate = $ts;

So, I think that the “default” ETag should simply be the mtime of the pageidx file. We’d have to use the RewriteMap directive with an External Rewriting Program.

Yikes! I’m not sure this is really faster… I guess it would be faster if the wiki itself was no longer using mod_perl (for whatever reasons). The external rewriting program would comparing the ETag header with the pageidx mtime and return a special value which would in turn be rewritten by a second rule to “redirect” to a 304 NOT MODIFIED response…

Something to consider for later.

As I’m writing this, I’m noticing that the server is slow. Check the current time, right, the five minutes before the full hour are a problem. Load reaching 6.

top - 17:59:18 up 4 days, 16:57,  1 user,  load average: 5.94, 5.41, 4.04
Tasks:  20 total,   1 running,  19 sleeping,   0 stopped,   0 zombie
%Cpu(s): 98.7 us,  1.3 sy,  0.0 ni,  0.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem:   4194304 total,  1688940 used,  2505364 free,        0 buffers
KiB Swap:  1048576 total,     4416 used,  1044160 free,  1331364 cached

  PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+  COMMAND           
 2635 www-data  20   0  470m 122m 4704 S 101.9  3.0  42:43.65 /usr/sbin/apach   
 4902 www-data  20   0  434m  91m 5360 S  72.6  2.2  21:12.41 /usr/sbin/apach   
    1 root      20   0 10608  196   60 S   0.0  0.0   0:04.12 init              
    2 root      20   0     0    0    0 S   0.0  0.0   0:00.00 kthreadd/2828     
    3 root      20   0     0    0    0 S   0.0  0.0   0:00.00 khelper/2828      
  702 root      20   0 51560 9856 2068 S   0.0  0.2   0:11.56 munin-node        
 1790 messageb  20   0 29764  256   12 S   0.0  0.0   0:00.00 dbus-daemon       
 8703 root      20   0 71252 3664 2872 S   0.0  0.1   0:00.02 sshd              
 8707 alex      20   0 71252 1720  924 S   0.0  0.0   0:00.00 sshd              
 8708 alex      20   0 21256 4096 1712 S   0.0  0.1   0:00.05 bash              
 8723 alex      20   0 23120 1612 1188 R   0.0  0.0   0:00.00 top               
15874 root      20   0 71192 5168 1620 S   0.0  0.1   1:20.36 fail2ban-server   
15876 root      20   0 22260  908  672 S   0.0  0.0   0:06.63 gam_server        
19427 root      30  10 12252  956  792 S   0.0  0.0   0:00.00 rsync             
20367 root      20   0 49728 4624  712 S   0.0  0.1   0:19.49 rsyslogd          
21949 root      20   0 49892 1236  628 S   0.0  0.0   0:00.81 sshd              
22815 root      20   0 20368  496  364 S   0.0  0.0   0:01.23 cron              
25118 root      20   0  122m  10m 3932 S   0.0  0.3   0:01.28 /usr/sbin/apach   
27076 root      20   0 72564 2024  732 S   0.0  0.0   0:09.69 sendmail-mta      
29022 root      20   0 42984 2976 2148 S   0.0  0.1   0:18.03 monit             

A few minutes later load reached 7. And my processes aren’t busy.

top - 18:01:45 up 4 days, 16:59,  1 user,  load average: 6.65, 5.91, 4.43
Tasks:  24 total,   2 running,  22 sleeping,   0 stopped,   0 zombie
%Cpu(s): 97.2 us,  0.9 sy,  1.7 ni,  0.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.2 st
KiB Mem:   4194304 total,  1726856 used,  2467448 free,        0 buffers
KiB Swap:  1048576 total,     4416 used,  1044160 free,  1331376 cached

  PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+  COMMAND           
 4902 www-data  20   0  437m 108m 5384 S  61.6  2.7  22:46.97 /usr/sbin/apach   
 9105 munin     30  10  140m  23m 5936 R   3.3  0.6   0:02.26 munin-graph       
    1 root      20   0 10608  196   60 S   0.0  0.0   0:04.12 init              
    2 root      20   0     0    0    0 S   0.0  0.0   0:00.00 kthreadd/2828     
    3 root      20   0     0    0    0 S   0.0  0.0   0:00.00 khelper/2828      
  702 root      20   0 51560 9856 2068 S   0.0  0.2   0:11.57 munin-node        
 1790 messageb  20   0 29764  256   12 S   0.0  0.0   0:00.00 dbus-daemon       
 8703 root      20   0 71252 3664 2872 S   0.0  0.1   0:00.02 sshd              
 8707 alex      20   0 71252 1720  924 S   0.0  0.0   0:00.00 sshd              
 8708 alex      20   0 21256 4096 1712 S   0.0  0.1   0:00.05 bash              
 8723 alex      20   0 23120 1612 1188 R   0.0  0.0   0:00.06 top               
 8734 root      20   0 33032 1160  836 S   0.0  0.0   0:00.00 cron              
 8738 munin     20   0 10708 1388 1200 S   0.0  0.0   0:00.00 sh                
 8742 munin     20   0 10716 1392 1192 S   0.0  0.0   0:00.00 munin-cron        
15874 root      20   0 71192 5168 1620 S   0.0  0.1   1:20.38 fail2ban-server   
15876 root      20   0 22260  908  672 S   0.0  0.0   0:06.64 gam_server        
19427 root      30  10 12252  956  792 S   0.0  0.0   0:00.00 rsync             
20367 root      20   0 49728 4624  712 S   0.0  0.1   0:19.49 rsyslogd          
21949 root      20   0 49892 1236  628 S   0.0  0.0   0:00.81 sshd              
22815 root      20   0 20368  496  364 S   0.0  0.0   0:01.23 cron              
25118 root      20   0  122m  10m 3932 S   0.0  0.3   0:01.28 /usr/sbin/apach   
27076 root      20   0 72564 2024  732 S   0.0  0.0   0:09.70 sendmail-mta      
29022 root      20   0 42984 2976 2148 S   0.0  0.1   0:18.03 monit             

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Comments on 2014-12-25 Emacs Wiki Migration

So I’m thinking, why don’t you run some small benchmark (with apache turned off) to see how much of the CPU you’ve got? Or maybe even IO benchmark?– AlexDaniel 2014-12-26 11:00 UTC



AlexSchroeder
Yeah. I guess I was hoping that munin does this, effectively. I’ll have to check the plugins currently enabled and check whether they do what I think they do.

AlexSchroeder 2014-12-26 20:19 UTC

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2014-12-24 Emacs Wiki Migration

(Continued from yesterday.)

Current status:

  • Read-only server is up.
  • Monit restarts Apache practically every hour because of load.
  • As far as I am concerned, using nginx as a caching proxy isn’t as effective as some people have been suggesting.
  • I’m noticing monit restarting apache practically every hour. Is some other user on this shared host running an hourly job that borks the system? I must have misconfigured Apache such that the resulting performance dip results in a death spiral.

Here’s the munin graph that makes me suspect that I’m not getting all of the CPU I need. The gaps happen when load is so high that munin doesn’t get to run. Yikes!

https://farm8.staticflickr.com/7537/15911905077_b82b4056a0_o.png

Field
Info
system
CPU time spent by the kernel in system activities
user
CPU time spent by normal programs and daemons
nice
CPU time spent by nice(1)d programs
idle
Idle CPU time
iowait
CPU time spent waiting for I/O operations to finish when there is nothing else to do.
irq
CPU time spent handling interrupts
softirq
CPU time spent handling “batched” interrupts
steal
The time that a virtual CPU had runnable tasks, but the virtual CPU itself was not running

I think what happens is that somebody else on this server is taking up %CPU and this results in Apache processes piling up.

Here’s from the log files:

Dec 24 09:46:37 localhost monit[29022]: 'apache' trying to restart
Dec 24 09:46:37 localhost monit[29022]: 'apache' stop: /etc/init.d/apache2
Dec 24 09:46:38 localhost sm-mta[27076]: rejecting connections on daemon MTA-v4: load average: 71
...
Dec 24 13:02:55 localhost monit[29022]: 'apache' trying to restart
Dec 24 13:02:55 localhost monit[29022]: 'apache' stop: /etc/init.d/apache2
Dec 24 13:03:01 localhost sm-mta[27076]: rejecting connections on daemon MTA-v4: load average: 37
...
Dec 24 15:55:35 localhost monit[29022]: 'apache' trying to restart
Dec 24 15:55:35 localhost monit[29022]: 'apache' stop: /etc/init.d/apache2
Dec 24 15:55:43 localhost sm-mta[27076]: rejecting connections on daemon MTA-v4: load average: 27
...
Dec 24 16:54:16 localhost monit[29022]: 'apache' trying to restart
Dec 24 16:54:16 localhost monit[29022]: 'apache' stop: /etc/init.d/apache2
Dec 24 16:54:25 localhost sm-mta[27076]: rejecting connections on daemon MTA-v4: load average: 34
...
Dec 24 17:56:52 localhost monit[29022]: 'apache' trying to restart
Dec 24 17:56:52 localhost monit[29022]: 'apache' stop: /etc/init.d/apache2
...
Dec 24 21:56:02 localhost monit[29022]: 'apache' trying to restart
Dec 24 21:56:02 localhost monit[29022]: 'apache' stop: /etc/init.d/apache2
Dec 24 21:56:03 localhost sm-mta[27076]: rejecting connections on daemon MTA-v4: load average: 37

OK, so how do I make Apache more robust against those spikes?

The current settings:

# StartServers: initial number of server processes to start
# MinSpareThreads: minimum number of worker threads which are kept spare
# MaxSpareThreads: maximum number of worker threads which are kept spare
# ThreadLimit: ThreadsPerChild can be changed to this maximum value during a
#              graceful restart. ThreadLimit can only be changed by stopping
#              and starting Apache.
# ThreadsPerChild: constant number of worker threads in each server process
# MaxClients: maximum number of simultaneous client connections
# MaxRequestsPerChild: maximum number of requests a server process serves
# <IfModule mpm_worker_module>
#     StartServers          2
#     MinSpareThreads      25
#     MaxSpareThreads      75 
#     ThreadLimit          64
#     ThreadsPerChild      25
#     MaxClients          150
#     MaxRequestsPerChild   0
# </IfModule>
<IfModule mpm_worker_module>
    StartServers          2
    ServerLimit           3
    MinSpareThreads      25
    MaxSpareThreads      75
    ThreadLimit         100
    ThreadsPerChild     100
    MaxClients          300
    MaxRequestsPerChild  10000
</IfModule>

Nic said, I should drop those numbers to better match the cores I have available. Each thread actually running will do IO, so that’s an additional issue.

Two cores → no more than 2 servers. When a thread waits for the disk, another thread can run. How many more threads? Not many, because they will also need to use the disk. How about a 90% reduction: 10 threads per child. Looking at this German blog post again.

  • MaxClients = ServerLimit x ThreadsPerChild. OK.
  • MinSpareThreads = ThreadsPerChild * 3 to handle spikes – but I think more threads jumping in will lead us to a death spiral. Keeping this lower than 30!
  • MaxSpareThreads ≥ MinSpareThreads + ThreadsPerChild.
<IfModule mpm_worker_module>
    StartServers          1
    ServerLimit           2
    ThreadsPerChild      10
    MaxClients           20
    MinSpareThreads      10
    MaxSpareThreads      20
    MaxRequestsPerChild  10000
</IfModule>

Hours later. It seems to have worked? Load stable, hovering around 2 – this makes sense.

https://farm8.staticflickr.com/7532/16100535652_84b896b86a_o.png

All is not perfect, unfortunately. Monit says Apache has 6h uptime. That means somebody restarted Apache during the night. Damn.

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2014-12-23 Emacs Wiki Migration

(Continued from yesterday.)

Current status:

  1. Nic Ferrier set up a dedicated machine with nginx to act as a cache for emacswiki.org
  2. I’ve switched emacswiki.org to read-only for the moment (since you can only reach the front page anyway)
  3. I’ve pointed emacswiki.org to Nic’s machine instead of mine—as soon as this change reaches you, you should be using Nic’s cache
  4. Tomorrow, I’ll remove emergency URL rewrite which redirects all wiki requests except for the main page to http://emacswiki.org/load.html

Ideally, this would mean that we’ll see a read-only copy of emacswiki.org back up, soon. Once Nic and I figure out how to handle the cookie and the ETag stuff for Emacs Wiki, we can make the wiki editable again.

Note to self:

(Continued tomorrow.)

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2014-12-22 Emacs Wiki Migration

(Continued from yesterday.)

Well… I considered making this website mod_perl in order to reduce load. This morning it was incredibly high again. When I tried it, however, I ran into problems. Error messages indicated that my script wouldn’t compile. Something about ModPerl::Registry not being available (eventhough it seemed to work for Emacs Wiki), or links on my site pointing to Emacs Wiki. Something was getting mixed up? Does mod_perl not work when used for more than one script in a virtual hosting environment? I rolled back my changes and went to do whatever one does a few years before the year. As I came back, the situation doesn’t seem too bad:

https://farm8.staticflickr.com/7483/15459696234_a9351a5831_o.png

I’d prefer load around 2, but at least the site responds, most of the time.

Well, service continues to be lousy and I’m practically out of ideas. The next step looks like hacking Oddmuse to try and reduce file accesses and hits.

In the mean time, here’s the top of Apache’s server-info.

Server Version: Apache/2.2.22 (Debian) mod_ssl/2.2.22 OpenSSL/1.0.1e mod_perl/2.0.7 Perl/v5.14.2
Server Built: Jul 24 2014 15:34:03

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Current Time: Tuesday, 23-Dec-2014 00:25:10 CET
Restart Time: Tuesday, 23-Dec-2014 00:23:07 CET
Parent Server Generation: 0
Server uptime: 2 minutes 3 seconds
Total accesses: 482 - Total Traffic: 2.2 MB
CPU Usage: u83.27 s1.06 cu18.66 cs0 - 83.7% CPU load
3.92 requests/sec - 18.0 kB/second - 4705 B/request
9 requests currently being processed, 91 idle workers

W________________K_____________R_W_______K_K_W__________________
________________R__________________K............................
................................................W...............
................................................................
............................................

Scoreboard Key:
"_" Waiting for Connection, "S" Starting up, "R" Reading Request,
"W" Sending Reply, "K" Keepalive (read), "D" DNS Lookup,
"C" Closing connection, "L" Logging, "G" Gracefully finishing,
"I" Idle cleanup of worker, "." Open slot with no current process

That doesn’t really look very busy. So perhaps file access is the new bottle neck?

If you know some Perl, and if you know mod_perl, and you feel like you could help, please contact me!

The current setup uses a Linux OpenVZ / SolusVM VPS in Switzerland with 4096 MB RAM and 2 vCores (shared Dual Intel Xeon), 500 GB HDD (practically unused) Speicherplatz, with Debian Wheezy.

The Apache setup I mentioned previously:

<IfModule mpm_worker_module>
    StartServers          2
    ServerLimit           3
    MinSpareThreads      25
    MaxSpareThreads      75
    ThreadLimit         100
    ThreadsPerChild     100
    MaxClients          300
    MaxRequestsPerChild  10000
</IfModule>

The virtual server setup:

<VirtualHost *:80>
    ServerAdmin alex@emacswiki.org
    <Directory />
        Options None
        AllowOverride None
        Order Deny,Allow
        Deny from all
    </Directory>
    ServerName www.emacswiki.org
    ServerAlias emacswiki.org
    DocumentRoot /home/alex/emacswiki.org
    <Directory /home/alex/emacswiki.org>
        Options ExecCGI Includes Indexes SymLinksIfOwnerMatch
	AddHandler cgi-script .pl
        AllowOverride All
        Order Allow,Deny
        Allow from all
    </Directory>
    <Files emacs.pl>
       Options ExecCGI SymLinksIfOwnerMatch
       SetHandler perl-script
       PerlHandler ModPerl::Registry
    </Files>
    RewriteLog "/home/alex/logs/emacswiki.org/rewrite.log"
    RewriteLogLevel 0
    CustomLog /home/alex/logs/emacswiki.org/access.log combined
    ErrorLog  /home/alex/logs/emacswiki.org/error.log
    # LogLevel debug
    CustomLog /var/log/apache2/access.log vhost_combined
    ServerSignature On
</VirtualHost>

I run monit and munin for monitoring.

And now we’re getting into Oddmuse details. If you need more information in order to setup up a test environment, I’ll be happy to provide anything you need.

#! /usr/bin/perl
package OddMuse;
use CGI;
$q = new CGI;
$RunCGI = 0;
$UseConfig = 0; # no config!
$DataDir = '/home/alex/emacswiki';
if (not $config_loaded) {
  do '/home/alex/emacswiki.org/current.pl';
  do '/home/alex/emacswiki/modules/concat.pl';
  do '/home/alex/emacswiki/config';
  $config_loaded = 1;
}

# make sure traces of other language configs disappear
%Translate=();
$HomePage    = "SiteMap";
$RCName      = 'RecentChanges';
@UserGotoBarPages = ($HomePage, 'Search',
		     'ElispArea', 'HowTo', 'Glossary',
		     $RCName, 'News', 'Problems', 'Suggestions');
$EditNote = '<p>Please make sure you contribute only your own work. IP numbers are made available via the page history. If you want to keep it a secret, you need to use <a href="http://www.torproject.org/">Tor</a>. See <a href="/emacs/TextFormattingRules">TextFormattingRules</a> for how to format text. See <a href="/emacs/StyleGuide">StyleGuide</a> for the suggested writing style on this wiki.</p>';

# language specific files should only set variables, never redefine subroutines
$ConfigFile = "$DataDir/config-en";
# my $requested_language = "da, en-gb;q=0.8, en;q=0.7";
my $requested_language = $q->http('Accept-language');
my @languages = split(/ *, */, $requested_language);
my %Lang = ();
foreach $_ (@languages) {
  my $qual = 1;
  $qual = $1 if (/q=([0-9.]+)/);
  $Lang{$qual} = $1 if (/^([-a-z]+[a-z])/);
}
my @prefs = sort { $b <=> $a } keys %Lang;
# my $html = "input: $requested_language" . "\nResult: " . join(', ', map { "$_ ($Lang{$_})" } @prefs);
# print header, start_html, pre($html), end_html; exit;
foreach $_ (@prefs) {
  if (-r "$DataDir/config-$Lang{$_}") {
    $ConfigFile = "$DataDir/config-$Lang{$_}";
    last;
  }
}
do $ConfigFile;
# Do the wiki
DoWikiRequest();

(Continued tomorrow.)

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Comments on 2014-12-22 Emacs Wiki Migration

Completely unrelated, but if the majority of the traffic is anonymous, I would suggest installing Varnish

– Anonymous 2014-12-23 19:06 UTC



Alex Schroeder
I’m not sure. In my .htaccess, I already provide for long browser-side caching of static files:

ExpiresActive On
ExpiresDefault "access plus 1 hours"
ExpiresByType image/png "access plus 3 days"
ExpiresByType image/jpeg "access plus 3 days"
ExpiresByType image/svg+xml "access plus 3 days"
ExpiresByType text/css "access plus 3 days"

And the wiki itself uses ETags the way they were meant to be used, I think. See the wiki page on caching, if you’re interested. It’s true that returning the 304 code requires the wiki code to run, but I’m still saving on all the rendering. It’s worth a try, I guess. A short skimming of an intro page I found made me think that using it for wiki pages is going to involve some more work. Do you have some detailed instructions somewhere, or can you help in configuring Varnish for Oddmuse? The Varnish wiki page on ETags looks intimidating.

– Alex Schroeder 2014-12-23 20:33 UTC

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Define external redirect: LastUpdate