QuickCount

Unfortunately, it's currently notoriously difficult and expensive to get an exact count on large tables.

Luckily, there are some tricks for quickly getting fairly accurate estimates. For example, on a table with over 450 million records, you can get a 99.82% accurate count within a fraction of of the time. See the table below for an example dataset.

Supports:

• PostgreSQL
  • Multi-table Inheritance

SQL	Version	Result	Accuracy	Time
SELECT count(*) FROM small_table;	--	2037104	100.0000000%	4.900s
SELECT quick_count('small_table');	v0.0.5	1988857	97.63158877%	0.048s
SELECT quick_count('small_table');	v0.0.6	2036407	99.96578476%	0.050s
SELECT count(*) FROM medium_table;	--	81716243	100.0000000%	257.5s
SELECT quick_count('medium_table');	v0.0.5	79352284	97.10711247%	0.049s
SELECT quick_count('medium_table');	v0.0.6	81600513	99.85837577%	0.048s
SELECT count(*) FROM large_table;	--	455270802	100.0000000%	310.6s
SELECT quick_count('large_table');	v0.0.5	448170751	98.44047741%	0.047s
SELECT quick_count('large_table');	v0.0.6	454448393	99.81935828%	0.046s

These metrics were pulled from real databases being used in a production environment.

Installation

Add this line to your application's Gemfile:

gem 'quick_count'

And then execute:

$ bundle

Or install it yourself as:

$ gem install quick_count

To finish the install, in rails console:

$ QuickCount.install # Install with default (500000) threshold

Usage

# user.rb

QuickCount.install # Install with default (500000) threshold

# Change the threshold for when `quick_count` kicks in...
QuickCount.install(threshold: 500000)

class User < ActiveRecord::Base

end

User.quick_count

# Override the default threshold on a case-by-case basis.
User.quick_count(threshold: 600000)

Uninstallation

Remove this line to your application's Gemfile:

gem 'quick_count'

And then execute:

$ bundle

And in a rails console:

$ QuickCount.uninstall

License

Released under the MIT license - http://opensource.org/licenses/MIT

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/TwilightCoders/quick_count.

License

The gem is available as open source under the terms of the MIT License.