{ Josh Rendek }

I was writing some cucumber features for reru_scrum when I ran into an issue with destroying user records and Mysql2 throwing a Lock error.

The full error:

1Mysql2::Error: Lock wait timeout exceeded; try restarting transaction: UPDATE `users` SET `last_sign_in_at` = '2011-11-22 00:06:32', `current_sign_in_at` = '2011-11-22 00:11:28', `sign_in_count` = 3, `updated_at` = '2011-11-22 00:11:28' WHERE `users`.`id` = 1

A simple solution is to use the database_cleaner gem.

Inside your features/support/env.rb file:

1begin
2  require 'database_cleaner'
3  require 'database_cleaner/cucumber'
4  DatabaseCleaner.strategy = :truncation
5rescue NameError
6  raise "You need to add database_cleaner to your Gemfile (in the :test group) if you wish to use it."
7end

When defining a event listener for objects in Coffeescript you nede to make sure you use a -> – using a => will result in any references to attr() be “undefined”

Here is an example of some correct on click bindings that use the attr() methods

1  jQuery ($) ->
2  $('[id^=story_]').click ->
3    $( "#" +  $(this).attr("id") + "_loader")
4      .load('/projects/' + $(this).attr('project_id') +
5      '/story_types/' + $(this).attr('story_type_id') +
6      '/stories/'+ $(this).attr('story_id') + '/tasks/new')

If you run into an issue with bundler always installing into a directory then you may have accidentily run:

1bundle install foobar

You can run:

1bundle install --system

To go back to installing gems to the system/RVM path.

 1class RenderHelper
 2  class << self
 3    def render(assigns, options, request = {})
 4      request = {
 5        "SERVER_PROTOCOL" => "http",
 6        "REQUEST_URI" => "/",
 7        "SERVER_NAME" => "localhost",
 8        "SERVER_PORT" => 80
 9      }.merge(request)
10
11      av = ActionView::Base.new(ActionController::Base.view_paths, assigns)
12
13      av.config = Rails.application.config.action_controller
14      av.extend ApplicationController._helpers
15      av.controller = ActionController::Base.new
16      av.controller.request = ActionController::Request.new(request)
17      av.controller.response = ActionController::Response.new
18      av.controller.headers = Rack::Utils::HeaderHash.new
19
20      av.class_eval do
21        include Rails.application.routes.url_helpers
22      end
23
24      av.render options
25    end
26  end
27end

Usage

1 html_output = RenderHelper.render({:instance_variable1 => "foo",
2                                                :instance_variable2 => "bar"},
3                                                :template => 'view_to/render')

You can then use you’re favorite PDF generator (I use PDFKit) to take the html output and parse it to a PDF.

Earlier today I had a MySQL slave go down for a few hours, which wasn’t a big deal. When it was brought back up it wasn’t syncing properly:

1Seconds_Behind_Master: NULL

Apparently there was an issue with a query that was showing up under LAST_ERROR; running

1STOP SLAVE;
2SET GLOBAL SQL_SLAVE_SKIP_COUNTER = 1;
3START SLAVE;

fixed the issue and then issued another SHOW SLAVE STATUS\G; and got the correct output:

1Seconds_Behind_Master: 27269

About half an hour later the slave was all caught up and replication was working again.

One of the interesting things about switching to a static site (even when I had cacheing and everything tuned in WP) is the load times.

Requests per second

• Wordpress: 9.5
• Jekyll: 182.96

Time per request

• Wordpress: 2631.395 ms
• Jekyll: 245.954 ms

Time per request (across all concurrent)

• Wordpress: 105.256 ms
• Jekyll: 5.466 ms

Basically jekyll is about 1000-2000% faster at rendering pages.

Thats about it on what I really cared about… the website now loads blazingly fast and Jekyll is awesome to write in with markdown.

While I love WordPress - I think it was a bit of overkill for what I was doing on this blog so I converted everything to Jekyll, and threw all my images up on Amazon’s S3. I’ve also migrated all the comments over to Disqus.

One of the problems I ran into was getting the URLs to map the same; the _config.yml that worked for me was:

1pygments: true
2markdown: rdiscount
3permalink: /:year/:month/:title
4paginate: 10

And then to get my /apps/ working again I made a directory structure like this:

 1apps//bluebug:
 2BlueBug.zip	index.markdown
 3
 4apps//greenmail:
 5index.markdown
 6
 7apps//light_logify:
 8index.markdown
 9
10apps//pyultradns:
11index.markdown
12
13apps//quote-of-the-day-tweeter:
14index.markdown
15
16apps//rails_rrdtool:
17index.markdown
18
19apps//server-setup-fu:
20index.markdown
21
22apps//servly:
23index.markdown
24
25apps//ventrilo-ping-analyzer:
26index.markdown

Thankfully the issue tracker on Github was a great help, but I recently ran into two issues I’ve never had the pleasure of encountering before while using DJ:

“nil is not a symbol” as a failure message. When running the background jobs for Servly, this was occurring on the status checks (its a pretty long list of checks on a server to reduce false positives, including distributed pings).  The problem with having the longer definition was the way DJ serializes the ruby code to store in the database. It was originally using a TEXT(65535) field as the data type in MySQL – changing this to LongText fixed the issue. The mysterious part about this whole issue was it would run fine from the console, but not from the workers (which makes sense in hindsight because of the limited space available for the serialized object in the delayed_job table).

Its 2011 and Pandora hasn’t heard about expandable layouts… I love pandora, but their interface just sucks. It especially sucks when you have a huge list of stations.

Do something with all my screen real estate, please!

Graphing objects client side is a great way to avoid generating them server side (since client side scales infinitely). You do however run into issue when you get into thousands, or hundreds of thousands of points (for example displaying 5 minute intervals in a month: 8928). When graphing this many points javascript can hang or cause the browser to seem like its not responding.

This is a simple solution that I’ve been using for a while to average data points from a Active Record model:

 1def generic_graph(column, hours, multiplier = 1)
 2    beginning = Time.now.advance(:hours => -hours)
 3    x = YourModel.where("created_at > ?", beginning
 4    arr = []
 5    timeoffset = Time.zone.utc_offset/(60*60)
 6    Time.now.dst? ? timeoffset += 1 : 0
 7
 8    if hours >= 48 #or whatever number works for you
 9      x.collect.each_with_index do |s,y|
10        tmp_averaged = x[y..y+24].map{|ss| ss[column] } # collect 24 (or however many you want) records, then average them
11        arr << [s.created_at.advance(:hours=>timeoffset).to_i*1000, tmp_averaged.average] # this is for going into the flot.js graphing library
12      end
13    else
14      x.collect { |s| arr << [s.created_at.advance(:hours=>timeoffset).to_i*1000, s[column] ] }
15    end
16
17    arr.to_s #output for flot
18  end