Awesome

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.