Oddmuse

Oddmuse is the wiki engine running all the wikis at emacswiki.org – including EmacsWiki itself. My main interests are:

See OddmuseRoadmap for my thoughts about the design of Oddmuse.

2016-06-15 Oddmuse and Windows

Today I ran the Oddmuse test suite on Windows and it worked! I am amazed.

All tests successful.
Files=136, Tests=2907, 1028 wallclock secs ( 0.41 usr  0.45 sys + 211.30 cusr 219.98 csys = 432.14 CPU)
Result: PASS

I had already installed Cygwin and had used it to install Perl v5.22.2. I don’t think I ever ran cpan on this system because I had to set it up. It created $USERPROFILE/AppData/Roaming/perl5/ for me and set up local::lib.

And then I started installing.

I needed some libraries and a compiler which I installed via Cygwin. I already had the diff utils installed, but perhaps you never needed them. Oddmuse needs them.

diffutils
gcc-g++
libcrypt-devel
libexpat-devel
libxml2-devel
libgd-devel
libdb-devel

Then I started by installing cpanm.

cpan App::cpanminus

I had to add /usr/local/bin to my PATH.

cpanm CGI XML::Atom IO::Pipely Mojolicious Mojolicious::Plugin::CGI Toadfarm HTTP::Server::Simple Pod::Strip Crypt::Rijndael Crypt::Random::Seed RPC::XML HTML::Template Capture::Tiny MLDBM Captcha::reCAPTCHA DB_File XML::LibXML GD Time::ParseDate

And with that, I could finally run prove t. I’ll note, however, that make test caused t/big-brother.t to fail, perhaps because it runs with 4 jobs which overwhelmed my machine.

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Comments on 2016-06-15 Oddmuse and Windows

Perhaps add that info here: https://oddmuse.org/wiki/Unit_Testing ?

– AlexDaniel 2016-06-17 20:18 UTC


Good idea.

– Alex Schroeder 2016-06-17 21:00 UTC

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2015-10-09 Oddmuse and Mojolicious

I’m trying to run Oddmuse within a Perl web framework: Mojolicious using Mojolicious::Plugin::CGI. It won’t be as perfect as a true Mojolicious app, but it will still be much faster than a simple CGI script. When running as a CGI script, every request loads Perl and compiles all the modules – including the CGI module itself – and Oddmuse and the config files. When running under Mojolicious, we no longer load Perl and we compile Oddmuse just once. Oddmuse itself will keep loading the config file and all that, but it’s still much better than before. The Mojolicious app itself is then started by Toadfarm. And in order to force myself to test it, I’ve switched this wiki over to the new setup!

First, tell Apache to act as a reverse proxy and pass all /wiki requests to the new server. The two ProxyPass instructions at the bottom are the important bits:

<VirtualHost *:80>
    ServerName alexschroeder.ch
    ServerAlias www.alexschroeder.ch
    Redirect permanent / https://alexschroeder.ch/
</VirtualHost>
<VirtualHost *:443>
    ServerAdmin alex@alexschroeder.ch
    <Directory />
        Options None
        AllowOverride None
        Order Deny,Allow
        Deny from all
    </Directory>
    ServerName alexschroeder.ch
    ServerAlias www.alexschroeder.ch
    ServerAlias rpg.alexschroeder.ch
    DocumentRoot /home/alex/alexschroeder.ch
    <Directory /home/alex/alexschroeder.ch>
        Options ExecCGI Includes Indexes MultiViews SymLinksIfOwnerMatch
        AddHandler cgi-script .pl
        AllowOverride All
        Order Allow,Deny
        Allow from all
    </Directory>

    SSLEngine on
    SSLCertificateFile      /home/alex/ssl/alexschroeder.crt
    SSLCertificateKeyFile   /home/alex/ssl/alexschroeder.key
    SSLCertificateChainFile /home/alex/ssl/GandiStandardSSLCA2.pem
    SSLVerifyClient None

    ProxyPass /wiki             https://alexschroeder.ch:8080/wiki
    ProxyPass /mojo             https://alexschroeder.ch:8080/mojo

</VirtualHost>

Toadfarm setup in ~/farm/farm:

#!/usr/bin/env perl
use Toadfarm -init;

logging {
  combined => 1,
  file     => "farm.log",
  level    => "info",
};

# other apps go here...

mount "$farm/alexschroeder.pl" => {
  "Host" => qr{^(www.)?alexschroeder\.ch$},
  mount_point => '/wiki',
};

plugin "Toadfarm::Plugin::AccessLog";

start; # needs to be at the last line

The above means that all requests to htpp://alexschroeder.ch:8080/wiki and htpp://www.alexschroeder.ch:8080/wiki will be handled by Oddmuse.

Mojolicious wrapper in ~/farm/alexschroeder.pl:

#! /usr/bin/env perl

use Mojolicious::Lite;

plugin CGI => {
  support_semicolon_in_query_string => 1,
};

plugin CGI => {
  route => '/',
  script => 'wiki.pl', # ~/farm/wiki.pl
  env => {WikiDataDir => '/home/alex/alexschroeder'},
  errlog => 'alexschroeder.log', # path to where STDERR from cgi script goes
};

app->start;

In this case, wiki.pl is simply the original Oddmuse script, unchanged. :)

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Comments on 2015-10-09 Oddmuse and Mojolicious

Cool! That’s interesting.

What about side effects? Like, if you forget to initialize some variable somewhere, what is going to happen? (Thinking about mod_perl and all stuff related to it)

Also, I miss one important thing from your report… What about page load time? How much faster is it right now, comparing to regular cgi script?

– AlexDaniel 2015-10-09 11:21 UTC


I did not measure page load time. I also think that it keeps forking to run the script, so globals start empty every time? Not sure about the details. I haven’t seen any side effects, yet. Let me know if you see anything!

– Alex Schroeder 2015-10-09 11:39 UTC


Could you be so kind to measure the load time?

– AlexDaniel 2015-10-09 11:50 UTC


I think I was under the illusion that it was working. Now it is working. Hah! I had to rename my old wrapper script to realize that my ProxyPass instructions had been wrong.

Things to remember:

Check the config file for weird stuff.

# if ($ENV{SERVER_PORT} == 8080) {
#   $ScriptName  = 'https://alexschroeder.ch:8080/wiki';
#   $FullUrl     = 'https://alexschroeder.ch:8080/wiki';
# }

Make sure the user running toadfarm can write alle the files in your data directory. In my case, the data directory belongs to www-data.alex but there were temp files that alex could not write.

– Alex Schroeder 2015-10-09 13:27 UTC


Hm. Current setup, I get more or less the same time when I look at network analysis with my browser when I’m loading /wiki/About and when I’m loading /wiki2/About with wiki2.pl being my old wiki.pl wrapper script. I get numbers between 200ms and 700ms. I do note that /wiki/About keeps getting me a 200 OK response instead of a 304 NOT MODIFIED. I’m not quite sure what the problem is.

– Alex Schroeder 2015-10-09 13:40 UTC


Oh, and the code shows that our script is being exec’d. I’m not sure about the headers. I think if our script prints HTTP headers, we should be fine.

– Alex Schroeder 2015-10-09 13:47 UTC


Well, at least it seems to work right now. I think I got confused about the various restarts required.

The missing 304 NOT MODIFIED remains a mistery, however. I’ve tried $q = new CGI; $q->nph(1) in the config file, $CGI::NPH = 1 in the config file, CGI::nph(1) in the config file, use CGI qw/-utf8 -nph/ in the core script, and print $q->header(-nph=>1, -status=>'304 NOT MODIFIED') and return if PageFresh(); in the core script, reloading my toadfarm between edits and found no change.

When I tried to export MOJO_PLUGIN_CGI_DEBUG=1 before starting the toadfarm, I got a 503 error when visiting the site.

This is very annoying.

– AlexSchroeder 2015-10-09 14:32 UTC


OK, so the question is: How often is 304 NOT MODIFIED actually used?

alex@kallobombus:~/farm$ sudo wc -l /var/log/apache2/access.log.1
259852 /var/log/apache2/access.log.1
alex@kallobombus:~/farm$ sudo grep ^oddmuse /var/log/apache2/access.log.1 | wc -l
32867
alex@kallobombus:~/farm$ sudo grep "^oddmuse.*GET /wiki.* 304 " /var/log/apache2/access.log.1 | grep -v feed | wc -l
270

Filtering out feed request we’re down to 8‰.

For my own site:

alex@kallobombus:~/farm$ sudo grep ^alexschroeder /var/log/apache2/access.log.1 | wc -l
79286
alex@kallobombus:~/farm$ sudo grep "^alexschroeder.*GET /wiki.* 304 " /var/log/apache2/access.log.1 | grep -v feed | wc -l
702

This reduces the percentage to 9‰.

So, if we redirect feed requests to files and use a cron job to produce some of them, the 304 NOT MODIFIED response seems to be something we can do without, even if I think it ought to work.

– AlexSchroeder 2015-10-09 14:54 UTC


In other words, no noticeable performance boost? Do I read it right? But then why bother?

– AlexDaniel 2015-10-09 21:26 UTC


Hehe, indeed. The point is, however, that I want some sort of plan that will allow me to incrementally develop a solution. Mojolicious::Plugin::CGI does a lot of what I want. It integrates into Mojolicious and thus it can do logging, forking, and so on. It handles input and output. The only thing that’s missing is that it exec’s the script – loading Perl and compiling all the modules on every request.

I think I’ll try and modify the Plugin for my purposes. Then it’ll require Oddmuse once and just run DoWikiRequest on every request, mod_perl style.

– AlexSchroeder 2015-10-10 07:40 UTC


These are the changes I had to make to Mojolicious::Plugin::CGI: Add run option for a code reference and Make sure the status code is actually used and Add HTTP_IF_NONE_MATCH to environment.

This is the new server script I used:

#! /usr/bin/env perl

use lib '/Users/alex/src/mojolicious-plugin-cgi/lib';

use Mojolicious::Lite;

plugin CGI => {
  support_semicolon_in_query_string => 1,
};
 
plugin CGI => {
  route => '/wiki',
  script => 'wiki.pl',
  run => \&OddMuse::DoWikiRequest,
  before => sub {
    $OddMuse::RunCGI = 0;
    $OddMuse::DataDir = '/tmp/oddmuse';
    require 'wiki.pl' unless defined &OddMuse::DoWikiRequest;
  },
  env => {},
  errlog => 'wiki.log', # path to where STDERR from cgi script goes
};

get '/' => sub {
  my $self = shift;
  $self->redirect_to('/wiki');
};
 
app->start;

– AlexSchroeder 2015-10-11 06:51 UTC


With the above setup now installed on alexschroeder.ch, I’m getting response times of 150–230ms when looking at /wiki/About (and a 304 Not Modified response). The old CGI setup under /wiki2/About is giving response times of 250–720ms.

So, much better?

I’ve also started noticing the first signs of trouble: Edit page, save, look at it (looks good), edit page again and notice that it’s showing the old text, not the new text.

– AlexSchroeder 2015-10-11 10:28 UTC


When I tried it with this page, I saw my browser requesting the page using the following:

GET /wiki?action=edit;id=Comments_on_2015-10-09_Oddmuse_and_Mojolicious HTTP/1.1
...
If-None-Match: 1444395217%1e1%1eAlexSchroeder%1ekensanata%40gmail.com

Oddmuse replied with a 304 Not Modified and the content was wrong. As I checked, however, the timestamp of the index file does in fact match:

alex@kallobombus:~/alexschroeder$ date -r pageidx +%s
1444395217

Looking at the log of recent changes, however:

alex@kallobombus:~/alexschroeder$ tail -n 1 rc.log
1444559479Comments_on_2015-10-09_Oddmuse_and_Mojolicious1With the above setup now installed on alexschroeder.ch, I'm getting response times of 150–230ms when looking at wikiAbout (and a 304 Not Modified response). So, much better? 127.0.0.1AlexSchroeder23en

I guess something about TouchIndexFile isn’t working.

sub TouchIndexFile {
  my $ts = time;
  utime $ts, $ts, $IndexFile;
  $LastUpdate = $Now = $ts;
}

I’ve made sure that all the files belong to alex.alex instead of www-data.alex. And that seems to help. After saving:

alex@kallobombus:~/alexschroeder$ date -r pageidx +%s
1444560771
alex@kallobombus:~/alexschroeder$ tail -n 1 rc.log
1444560771Comments_on_2015-10-09_Oddmuse_and_MojoliciousWhen I tried it with this page, I saw my browser requesting the page using the following: {{{ GET wiki?action=edit;id=Commentson2015-10-09OddmuseandMojolicious HTTP1.1 … If-None-Match: 1444395217%1e1%1eAlexSchroeder%1ekensanata%40gmail.com }}} Oddmuse replied with a 304 Not Modified and the content…127.0.0.1AlexSchroeder24en

And the next request:

GET /wiki?action=edit;id=Comments_on_2015-10-09_Oddmuse_and_Mojolicious HTTP/1.1
...
If-None-Match: 1444395217%1e1%1eAlexSchroeder%1ekensanata%40gmail.com

HTTP/1.1 200 OK
...
Etag: 1444560771%1e1%1eAlexSchroeder%1ekensanata%40gmail.com
...

Yay?

– AlexSchroeder 2015-10-11 10:52 UTC


OK, added one final patch to make it work without having to use the -nph option for the CGI library and submitted a pull request. And I installed it for this site as well. “Eat your own dog food,” and all that.

– AlexSchroeder 2015-10-11 12:41 UTC


Wow, many more commits after talking to the maintainer.

– AlexSchroeder 2015-10-11 16:14 UTC

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2015-06-14 Go Oddmuse

Sometimes I wonder whether I should move Oddmuse away from Perl 5 to something else. Something I would like to learn. An opportunity to redo everything, from scratch. Not many people are using Oddmuse, so I might as well write something else, for myself.

I recently read Writing Web Applications for Go, where they develop a simple wiki. I wondered about storing the data in a git repository. I found git2go. Hm…

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Comments on 2015-06-14 Go Oddmuse

Perl 6 is an obvious candidate. And yes, they did not just change print ‘x’ to print(’x’) like they did in Python, it is a completely new language that you have to learn.

Speaking of Go, there is a great video called Perl 6 for Mere Mortals, and here is a direct link to a part of it which is somehow :) related to Go. That’s not a meaningful comparison, but it should give you the idea. You can also watch that video from the beginning, it is very interesting if you have not investigated into Perl 6 yet.

Now, if we think about all of the languages out there, what are the actual features that are required for Oddmuse?

Well, since Oddmuse is all about parsing the wiki text, you need some tools for parsing. Perl 5 has regexes (um, okay), Perl 6 has grammars (exactly what we need!), and Go has something as well (like this, which is, again, verbose as hell), but I’m not an expert. You can also use libs, but having a built-in support is probably advantageous.

Somehow I can’t really think of any other criteria, everything else probably exists in every other language out there. You might also say “performance” but the only website suffering from that is probably emacswiki, and it all depends on your actual goals – for example, better execution time can be achieved by using concurrency, which does not really lead to better CPU time. Concurrency in Perl 6 – yes (but maybe just a bit flaky at the moment), performance in Perl 6 – well, not now, but the potential is there (i.e. gradual typing).

In other words: what is the motivation? “Just to learn” is not going to get you anywhere, not even make you learn something (learning to find reasons for doing stuff (i.e. causation) is part of the learning, doing stuff purposelessly is harmful to the thinking process).

AlexDaniel 2015-06-14 14:05 UTC


Perhaps Go just makes me want to delve into the low level stuff. I like the post about Handwritten Parsers & Lexers in Go. :)

I keep thinking about all the design decisions. Filenames are pagenames. Namespaces are subdirectories. Can we switch to “git first”? No more log files. We no longer need keep files. How would modules work? Would you simply recompile the wiki? Dynamic linking? Would I want to use a templating architecture? People seem to like that. Was “printing as we go” a good decision? Perhaps it no longer matters much.

I need to think about extensibility of Cajun, the Wiki Creole lexer and parser.

– Alex Schroeder


These are very good questions. Maybe you should write down these ideas on Oddmuse: Revolutionary Changes.

  • “git first” – Yea, but… This would effectively break the goal of having one script file that just works (and I think that this is more important than having no recent changes and keep files logic in the core).
  • “How would modules work? Would you simply recompile the wiki?” – this would effectively throw away all of the nice things like Module Updater or Module Bisect (or at least make them much harder to implement). It will also break the potential of a few other ideas that keep floating in my head. In other words, “simply recompile the wiki” is not that simple.
  • “Would I want to use a templating architecture? People seem to like that.” Yea, but… It seems like if we switch to Perl6 then the core will collapse into a small piece of code with all of the irrelevant stuff separated into grammars or other classes, or maybe just tiny subroutines. Which brings us to the next point…
  • “Was “printing as we go” a good decision? Perhaps it no longer matters much.” – Good decision, but it really depends on your understanding of “as we go”. For example, what if we parse the wiki text first, before printing anything except the header? Then, once we start processing the parsed text, we can print stuff as we go. That’s exactly how it will work in perl6 (at least, that’s the easiest way) – first you slam the wiki text into your grammar and wait for it to be processed (oh by the way, while this is happening you can actually do other stuff asynchronously, like start reading the tag index or whatever). Then, when your wikitext is parsed, you can start deciding what to print now. And this is so much better than what we have now. Want to print table of contents? Just take the required information from the match object, no need for dirty hacks. In other words, in perl6 it is very easy to have parsing and actions separately, which is beneficial in many ways. But at the same time, once you start processing the actions you can start printing as you go (which makes sense, what if there is some complex search stuff included on the page, you’d probably want to see at least half of the page while this is going).

AlexDaniel 2015-06-16 00:22 UTC


And yeah, if you are seriously thinking about Go, what if we make a comparison table with Perl6 and Go, and the relevant language features? Both of the languages have some interesting stuff to offer, for example Perl6 to JS and Go to JS. And there are definitely some winning points for Go, especially associated with execution time and maturity.

AlexDaniel 2015-06-16 00:31 UTC


Hehe, I think you and Oddmuse: Revolutionary Changes is what started this all! I looked at Oddmuse as a “mission accomplished” project. With the migration of Emacs Wiki I’ve realized that a big site might want to serve its own pages without running a web server. I tried to understand PSGI/Plack in order to have Perl run Oddmuse like a web application. When I saw the wiki tutorial for Go, and how I got a web server up and running in no time, and how easy it was to include some basic markup, I was thrilled! Sure, the code doesn’t have a lot of features. But it beats the SmallestWiki candidates. :)

You arguments in favor of some of the core architecture decisions made for Oddmuse are good – and your hopes for Perl 6 and improved parsing are infectious! I’m very much looking forward to Perl 6.

– Alex Schroeder 2015-06-16 06:02 UTC


It’s also cool to look at the TinyWiki source code again and rediscover why I rewrote the Usemod Wiki style search and replace code with the extensible state machine code we have right now.

– Alex Schroeder 2015-06-16 08:00 UTC

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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://alexschroeder.ch/pics/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://alexschroeder.ch/pics/15960447830_a102ae6df7_o.png

https://alexschroeder.ch/pics/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://alexschroeder.ch/pics/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


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://alexschroeder.ch/pics/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://alexschroeder.ch/pics/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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