High CPU Usage when generating PDFs in Rails with Wicked_PDF gem - ruby-on-rails

Question

I'm trying to generate a PDF file with Rails, but when I do I notice my system CPU starts to max out. Initially, it will go from ~2.5% then increase to ~65%-$80% for a steady period of time and then finally max out almost prior to displaying them PDF in my iframe on my page. Here are some messages I get when monitoring the memory usage on my system:
Warning or critical alerts (lasts 9 entries)
2017-06-09 14:58:07 (0:00:04) - CRITICAL on CPU_SYSTEM (100.0)
2017-06-09 14:58:04 (0:00:13) - CRITICAL on CPU_USER (Min:72.8 Mean:83.3 Max:93.7)
2017-06-09 14:47:39 (0:00:06) - CRITICAL on CPU_USER (93.0)
2017-06-09 14:47:29 (0:00:04) - WARNING on CPU_SYSTEM (74.7)
2017-06-09 14:36:48 (0:00:04) - CRITICAL on CPU_SYSTEM (100.0)
2017-06-09 14:36:45 (0:00:10) - CRITICAL on CPU_IOWAIT (Min:78.6 Mean:85.7 Max:97.4)
2017-06-09 14:18:06 (0:00:04) - CRITICAL on CPU_SYSTEM (94.3)
2017-06-09 14:18:06 (0:00:07) - CRITICAL on CPU_USER (91.0)
2017-06-09 15:01:14 2017-06-09 14:17:44 (0:00:04) - WARNING on CPU_SYSTEM (73.8)
The gems I have installed for my PDF generation are wicked_pdf (1.0.6) and wkhtmltopdf-binary-edge (0.12.4.0). And the process with code for each are as follows:
controllers/concerns/pdf_player_reports.rb
def director_report_pdf
#players = Player.where(id: params["player_ids"]
respond_to do |format|
format.html
format.pdf do
render pdf: "#{params['pdf_title']}",
template: 'players/director_summary_report.pdf.erb',
layout: 'print',
show_as_html: params.key?('debug'),
window_status: 'Loading...',
disable_internal_links: true,
disable_external_links: true,
dpi: 75,
disable_javascript: true,
:margin => {:top => 7, :bottom => 7, :left => 6, :right => 0},
encoding: 'utf8'
end
end
players/director_summary_report.pdf.erb
<div class="document" style="margin-top: -63px;">
<% #players.each do |player| %>
<% reports = player.reports.order(created_at: :desc) %>
<% if player.is_college_player? %>
<%= render partial: 'college_director_report.html.erb', player: player %>
<% else %>
<%= render partial: 'pro_director_report.html.erb', player: player %>
<% end %>
<%= "<div class='page-break'></div>".html_safe %>
<% end %>
</div>
college_director_report.html.erb
<%= wicked_pdf_stylesheet_link_tag "application", media: "all" %>
<%= wicked_pdf_javascript_include_tag "application" %>
<% provide(:title, "#{player.football_name}") %>
<% self.formats = [:html, :pdf, :css, :coffee, :scss] %>
<style>
thead { display: table-row-group; page-break-inside: avoid }
tfoot { display: table-row-group; }
/*thead:before, thead:after { display: none; }*/
table { page-break-inside: avoid; }
tr { page-break-inside: avoid; }
.page-break {
display:block; clear:both; page-break-after:always;
}
.keep-together { page-break-before: always !important; }
.table-striped>tbody>tr:nth-child(odd)>td,
tr.found{
background-color:#e2e0e0 !important;
}
</style>
<div class="row">
<div class="col-xs-6">
<span>DIRECTOR SUMMARY</span>
</div>
<div class="col-xs-6 text-right">
<%= "#{player.full_name} / #{player.school.short_name}".upcase %>
<h1><%= "#{player.full_name(true)} (#{player.school.code})".upcase %></h1>
</div>
</div>
<div class="row">
<div class="col-xs-12">
<%= render 'directors_report_player_header', player: player %>
<%= render 'directors_report_workouts', player: player %>
<%= render 'directors_report_grades', player: player %>
<%= render 'legacy_directors_report_contacts', player: player %>
</div>
</div>
directors_report_player_header.html.erb
<table class="table table-condensed table-bordered">
<thead>
<tr>
<th>Name</th>
<th>School</th>
<th>#</th>
<th>Position</th>
</tr>
</thead>
<tbody>
<tr>
<td><%= player.full_name(true) %></td>
<td><%= player.school.short_name %></td>
<td><%= player.jersey %></td>
<td><%= player.position.abbreviation %></td>
</tr>
</tbody>
</table>
UPDATE
I ran an example PDF generator using the following and the CPU% is what ends up maxing out as shown below...
<table class="table table-condensed">
<thead>
<th>Number</th>
</thead>
<tbody>
<% (1..60000).each do |number| %>
<tr>
<td><%= number %></td>
</tr>
<% end %>
</tbody>
</table>

Answer 1

Putting this in a controller seems ill-advised because the minute you deploy this the request will take a significant time to generate and block other incoming requests for other pages.
You should separate this into two concerns. One job that generates the HTML, which could be this controller, and then a background task to convert that HTML into PDF format.
In your controller, trigger a job using DelayedJob or similar and then render a page that polls for the job having completed.
Then in your background job you're dealing with just the task of rendering the HTML to PDF, rather than being within a web request. Something along these lines:
class RendersReportPdf
def self.call player_ids
html = ReportsController.render :director_report_pdf, assigns: { players: Player.where(id: player_ids }
pdf = WickedPdf.new.pdf_from_string html
temp = Tempfile.new("#{Time.now.to_i}.pdf")
temp.write(pdf)
temp.close
temp.path
# Probably upload this to S3 or similar at this point
# Notify the user that it's now available somehow
end
end
If you do this, then you can rule out that the issue is with running WickedPDF from within your controller action, but also you're making sure your site will stay up if you have long-running requests.

Answer 2

So I wanted to post my solution for future visitors, but it's based off of #stef's solution - so thanks stef!
controllers/concerns/players_controller.rb
def generate_report_pdf
players = print_settings(params)
pdf_title = "#{params['pdf_title']} - #{Time.now.strftime("%c")}"
GeneratePdfJob.perform_later(players.pluck(:id), pdf_title, current_user.code, params["format"])
end
app/jobs/generate_pdf_job.rb
def perform(*args)
player_ids = args[0]
pdf_title = args[1]
user_code = args[2]
report_type = args[3]
generate_pdf_document(player_ids, pdf_title, user_code, report_type)
end
def generate_pdf_document(ids, pdf_title, user_code, report_type)
# select the proper template by the report type specified
case report_type
when "Labels"
html = ApplicationController.new.render_to_string(
template: 'players/board_labels.pdf.erb',
locals: { player_ids: ids },
margin: { top: 6, bottom: 0, left: 32, right: 32 }
)
when "Reports"
# ...
end
end
def save_to_pdf(html, pdf_title, user_code)
pdf = WickedPdf.new.pdf_from_string(
html,
pdf: "#{pdf_title}",
layout: 'print',
disable_internal_links: true,
disable_external_links: true,
disable_javascript: true,
encoding: 'utf-8'
)
pdf_name = "#{pdf_title}.pdf"
pdf_dir = Rails.root.join('public','uploads','reports',"#{user_code}")
pdf_path = Rails.root.join(pdf_dir,pdf_name)
# create the folder if it doesn't exist
FileUtils.mkdir_p(pdf_dir) unless File.directory?(pdf_dir)
# create a new file
File.open(pdf_path,'wb') do |file|
file.binmode
file << pdf.force_encoding("UTF-8")
end
end
With this way I then use an ajax call to keep checking the user's specified directory for new files, and I update the partial that lists out the files in the directory. The only thing I don't like is now I have to have a table list of the user's files. I'd rather just have the file get delivered to the client's browser for download instead - but have yet figured out how to get that to work.