N+1 query problem
- ORMs make it easy to a query per loop iteration, which we want to avoid
eager_load
- single query (left outer join)
- can reference the other table's columns in
where
preload
- a few queries (one per table)
- typically faster
/* | |
* 264 - Count on Cantor | |
* | |
* Given an input value N, print the Nth term in Cantor's enumeration. | |
* | |
* There may be a simpler closed form of this. However, what strikes me as | |
* possible right now is: we figure out what diagonal n is on, which gives us | |
* the beginning of that diagonal (1/2, 3/1, 1/4, 5/1, etc.). Then, we adjust | |
* the numerator and denominator based on the distance from the first term in | |
* the diagonal and the direction it takes (up-right for odd, down-left for |
/* | |
* Title | |
*/ | |
import java.io.BufferedOutputStream; | |
import java.io.BufferedReader; | |
import java.io.IOException; | |
import java.io.InputStreamReader; | |
public class Main { |
User name metrics | |
Bin width: 1 | |
Each # represents 500 users. | |
LENGTH OF FIRST NAME | |
==================== | |
bins: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63] | |
freqs: [36, 510, 2547, 5905, 10086, 11103, 9461, 5363, 3918, 2780, 3515, 3655, 3609, 3213, 2246, 1469, 968, 576, 410, 253, 189, 162, 102, 57, 51, 42, 31, 24, 15, 4, 1, 4, 2, 2, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1] | |
01: | |
02: # |
log = StringIO.new | |
ActiveRecord::Base.logger = Logger.new(log) | |
Gradescope::Application.config.colorize_logging = false | |
RSpec.configure do |config| | |
config.after :suite do | |
lines = log.tap(&:rewind).readlines.to_a | |
matching = lines.map do |line| | |
next unless line =~ /Load/ |
<?xml version="1.0"?> | |
<opml version="2.0"> | |
<head> | |
<ownerEmail>johnmikecip@gmail.com</ownerEmail> | |
</head> | |
<body> | |
<outline text="div#assignment-submission-app" > | |
<outline text="(modals)" /> | |
<outline text="<b>AssignmentSubmissionViewer</b>" _note="<b>div#assignment-submission-show</b>" > | |
<outline text="PageViewerContainer" _note="div#assignment-submission-viewer (merge with child if possible)" > |
table.fixed-header | |
table-layout: fixed | |
border-collapse: collapse | |
thead tr | |
display: block | |
position: relative | |
tbody | |
display: block | |
overflow: auto | |
width: 100% |
# Browserify 3rd-party React components found on npm | |
# (prevents React & ReactDOM from being bundled) | |
export PACKAGE='simple-react-modal' # npm package | |
export EXPORT_NAME='SimpleReactModal' # will end up on window with this name | |
mkdir project && cd project | |
npm init -f | |
npm install -D browserify react react-dom |
# Install VirtualBox guest additions on Ubuntu | |
# https://www.vagrantup.com/docs/virtualbox/boxes.html | |
VB_VERSION='5.0.20' | |
wget "http://download.virtualbox.org/virtualbox/$VB_VERSION/VBoxGuestAdditions_$VB_VERSION.iso" | |
sudo mkdir /media/VBoxGuestAdditions | |
sudo mount -o loop,ro "VBoxGuestAdditions_$VB_VERSION.iso" /media/VBoxGuestAdditions | |
sudo sh /media/VBoxGuestAdditions/VBoxLinuxAdditions.run | |
rm "VBoxGuestAdditions_$VB_VERSION.iso" |
N+1 query problem
eager_load
where
preload
❯ vi /usr/local/lib/ruby/gems/2.3.0/gems/pronto-0.8.2/lib/pronto/formatter/text_formatter.rb | |
# change line 17 to ... | |
# "[#{message.runner.title}] #{format_location(message)} #{format_level(message)}: #{message.msg}".strip | |
❯ pronto run -r reek | |
Running Pronto::Reek | |
[reek] app/decorators/course_membership_decorator.rb:21 I: Is controlled by argument 'current_user' (ControlParameter) |