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Optimistic Locking assumes that a database transaction conflict is very rare to happen. It uses a version number of the record to track the changes. It raise an error when other user tries to update the record while it is lock.

usage

Just add a lock_version column to the table you want to place the lock and Rails will automatically check this column before updating the record.

Pessimistic locking assumes that database transaction conflict is very likely to happen. It locks the record until the transaction is done. If the record is currently lock and the other user make a transaction, that second transaction will wait until the lock in first transaction is release.

usage

Fast/efficient approach:

-- execute("UPDATE posts SET comments_count = (SELECT count(1) FROM comments WHERE comments.post_id = posts.id)")
   -> 1.3197s

Slow/naïve approach:

Sending emails with ActionMailer and Sidekiq

Send email asynchroniously using Sidekiq.

ActionMailer

Create your mailer us usual:

Here is a list of scopes to use in Sublime Text 2/3 snippets -

ActionScript: source.actionscript.2
AppleScript: source.applescript
ASP: source.asp
Batch FIle: source.dosbatch
C#: source.cs
C++: source.c++
Clojure: source.clojure

	curl --include \
	--no-buffer \
	--header "Connection: Upgrade" \
	--header "Upgrade: websocket" \
	--header "Host: example.com:80" \
	--header "Origin: http://example.com:80" \
	--header "Sec-WebSocket-Key: SGVsbG8sIHdvcmxkIQ==" \
	--header "Sec-WebSocket-Version: 13" \
	http://example.com:80/

	namespace :codecov do
	desc 'Uploads the latest simplecov result set to codecov.io'
	task upload: :environment do
	require 'simplecov'
	require 'codecov'

	formatter = SimpleCov::Formatter::Codecov.new
	formatter.format(SimpleCov::ResultMerger.merged_result)
	end
	end

	class CategoriesController < ApplicationController
	include Behaveable::ResourceFinder
	include Behaveable::RouteExtractor

	# Response type.
	respond_to :json

	# Get categories.
	#
	# GET (/:categorizable/:categorizable_id)/categories(.:format)

	class MyJob < ActiveJob::Base
	queue_as :urgent

	rescue_from(NoResultsError) do
	retry_job wait: 5.minutes, queue: :default
	end

	def perform(*args)
	MyService.call(*args)
	end

	ARG ASSET_HOST
	RUN bundle exec rake ASSET_HOST=${ASSET_HOST} RAILS_ENV=production assets:precompile