You login to a Linux server with a performance issue: what do you check in the first minute?

uptime
dmesg | tail
vmstat 1
mpstat -P ALL 1
pidstat 1
iostat -xz 1
free -m
sar -n DEV 1
sar -n TCP,ETCP 1
top

Also see:

• How to get a rough picture about a Rails project
• How to examine an unknown Ruby object

Use this:

SELECT pg_database.datname as "database_name", pg_database_size(pg_database.datname)/1024/1024 AS size_in_mb FROM pg_database ORDER by size_in_mb DESC;

Want to see database sizes in MySQL ?

PostgreSQL offers a really handy field type: json. You can store any JSON there, in any structure.

While its flexibility is great, there is no syntactic sugar in Rails yet. Thus, you need to manually query the database.

Demo

# Given a Task model with 'details' json column
Task.where("details->>'key' = ?", "value") # matches where 'details' contains "key":"value"
Task.where("details->>'{a,b}' = ?", "value") # matches where 'details' contains "a":{"b":"value"}
Task.where("details->'a'->>'b' = ?", "value") # same as above, but vi...

rack-mini-profiler is a powerful Swiss army knife for Rack app performance. Measure SQL queries, memory allocation and CPU time.

This should probably not be loaded in production (the article recommends otherwise), but this looks like a useful tool.

There are cases when you need to select DOM elements without jQuery, such as:

• when jQuery is not available
• when your code is is extremely performance-sensitive
• when you want to operate on an entire HTML document (which is hard to represent as a jQuery collection).

To select descendants of a vanilla DOM element (i.e. not a jQuery collection), one option is to use your browser's native querySelector and [querySelectorAll](https://developer.mozilla.org/de/docs/We...

If you have many connections to your MySQL or MariaDB (as we have) you might want to filter the list you see when running a SHOW PROCESSLIST. To hide all sleeping processes, you can simply use grep as your pager:

\P grep -v "| Sleep"

There is an more advanced way by querying the information_schema database: Show MySQL process list without sleeping connections

CSS4 comes with :has. E.g. h1:has(b) would select all <h1> tags that contain a <b> tag.

This is implemented in no browser but the jQuery query engine already supports it as a custom extension.

A very informative and interesting presentation about browsing performance, looking at efforts Google Chrome takes to increase it.

From those slides

There is a bunch of interesting pages in Chrome:

• chrome://dns - List of prefetched DNS
• chrome://predictors/ - Chrome knows where you'll go

Preconnect

With <link rel="preconnect" href="https://the-domain.com"> in an HTML head, you give the browser an early hint that it will need to access the mentioned domain. By setting up the connection in advance, page load performance gets im...

Table of contents of the linked article:

What are Web Fonts?

• Advantages of Web Fonts
• Disadvantages of Web Fonts
  • Fallback Fonts
  • CSS3 @font Declaration Example
  • Fallback Font Example
  • Render Blocking and Critical Rendering Path
  • FOIT

Optimizing Web Font Delivery Further

• Prioritize Based On Browser Support
• Choose Only Styles You Need
• Character Sets
• Host Fonts Locally or Prefetch
• Store in LocalStorage with Base64 Encoding
• Another Method

Web Font Pe...

You can use mail-tester.com to check your application's e-mails for issues that might cause e-mails to be classified as spam.

They provide a one-time e-mail addresses that you can use to sign up etc. You can then check for scoring results of SpamAssassin and other potential issues.
You don't need to hit 10/10. Something around 9/10 is perfectly fine.

Note:

• For password-protected staging sites you will get an error for links that can not be resolved. This is fine, simply check production once available.
• ...

You can configure a stat socket for haproxy in the global section of the configuration file:

global
  daemon
  maxconn 999
  user foobar
  stats socket /var/run/haproxy.stat  # this is the line you want to configure

You need socat to query data from this socket.

After installing socat and reconfiguring haproxy you can use this socket to query data from it:

• show informations like haproxy version, PID, current connections, session rates, tasks, etc..

  echo "show info" | socat unix-connect:/var/run/haproxy.stat stdio
  

...

With "attaching an event handler once" you possibly mean one of these two things:

Register a function for an event, and discard it once that event has happened

Use one instead of on.

$(element).one('eventName', function() { ... });

It has the same API has on.

When code is run multiple times that registers a function for an event, do that only once

With jQuery, you can de-register callbacks. You can use that to achieve registering a function only once.

function myAction() { ... }; // defined somewhere globally o...

Note

This card does not reflect the current state of lazy loading technologies. The native lazy attribute could be used, which is supported by all major browsers since 2022.

Since images are magnitudes larger in file size than text (HTML, CSS, Javascript) is, loading the images of a large web page takes a significant amount of the total load time. When your internet connection is good, this is usually not an issue. However, users with limited bandwidth (i.e. on mobile) need to mine their data budget...

There are many solutions, but a very concise one is this:

hash.merge!(hash) do |key, old_value, new_value|
  # Return something
end

The block of merge! will be called whenever a key in the argument hash already exists in the base hash. Since hash is updated with itself, each key will conflict and thus allow you to modify the value of each key to whatever you like (by returning old_value you'd get the behavior of Rails' reverse_merge!, by re...

Quick steps

1. git rebase -i -> mark your commit with edit
2. git reset HEAD~ (remove the marked commit, but keep its changes)
3. Make several commits (optionally setting the previous author manually)
4. git rebase --continue

Detailed instructions

Basically, you will review the last n commits and stop at the splittable commit. Then you'll undo that commit and put its changes into new commits at your liking.

1. Review commits (rebase)

   git rebase -i HEAD~3
   # or
   git rebase -i origin/master
   

   ...

One useful postgres command I stumbled upon recently was \x. It gives you an expanded display which allows you to actually read the results of your select * from queries. The link below describes a few more useful techniques and commands.

You want to test your 1GE or 10GE internet uplink? We needed to ensure we have full 10GE to the backbone for a customer project.

Using netcat

To test whether we can achieve the bandwidth internally, you can use netcat and dd like this:

On your first server: nc -v -l 55333 > /dev/null
On your second server: dd if=/dev/zero bs=1024K count=5000 | nc -v $remote_ip 55333

You should see some output like this:

user@xxx:~ % dd if=/dev/zero bs=1024K count=5000 | nc -v removed 55333
Connection to 91.250.95.249 55333 port [...

When dealing with AR scopes, you can remove conditions, order, etc by using the unscope method.

It is available on Rails 4+.

Examples

Consider an exemplary User class as follows. For the examples below, we will use a scope that applies all its constraints.

class User < ActiveRecord::Base
  scope :active, -> { where(locked: false) }
  scope :admins, -> { where(role: 'admin') }
  scope :ordered, -> { order(:name) }
end

users = User.active.admins.ordered

^
SELECT "users".* FROM "users" WHERE "use...

Redactor is yet another WYSIWYG editor. It definitely has its weak points, but I want to point out that it has clear strengths, too.

Pro

• Simple and beautiful interface.
• Outstandingly organized source code. Have never seen a JS library that was this structured.
• Clear, comprehensive and searchable API documentation. Filled with code examples.
• Easily customizable: specify toolbar buttons, pass various callbacks, etc.
• Features a collection of great [plugins](ht...

PostgreSQL's array data type is pretty useful, but manipulating values of arrays can be awkward because of its syntax.

Consider the following users table which each example below will start from:

(PostgreSQL uses curly braces to represent arrays, true story.)

Adding values

Use the array_cat function, or the || operator.

These calls will add the values "cats" and "mice" to use...

Rails 4 introduced raising an error on pending migrations. This is most annoying when you are crafting a migration but need to play with your application to figure out how to do it.

To disable this behavior, just set the corresponding config option to false:

# in config/environments/development.rb

# Raise an error on page load if there are pending migrations.
config.active_record.migration_error = false # was :page_load

Web fonts are great. They are also be really bad for front-end performance because they block rendering. You may have experienced this on a slow cellular network. Staring at a blank page is no fun, especially when the content has already loaded.

This talk explores why browser have placed fonts on the critical path, and how we can work around this while still delivering a good user experience. It also takes a look at what the future will bring to web font performance: preloading hints, the font-display property, and HTTP/2.

Our applications not only need to be functional, they need to be fast.

But, to quote Donald Knuth,

premature optimization is the root of all evil (or at least most of it) in programming

The reasoning is that you should not waste your time optimizing code where it does not even matter. However, I believe there are some kinds of optimizations you should do right away, because

• they are either obvious and easy
• or they are very hard to do optimize later

This is an attempt to list some of those things:

On the server

...

This is a guide on how to effectively use Git when working on a feature branch. It is designed to get out of your way as much as possible while you work, and ensure you end up with clean commits in the end.

We assume you are the only person working on this branch. We also assume the branch has never been "partially" merged into master.

You want to start a feature branch

git checkout master
git checkout -b my-feature-branch
git push -u origin my-feature-branch

You've added code that works ind...