quick_random_records is a Ruby Gem that empowers ActiveRecord Model to return random records fast when your table has lots of records but few deleted records.

Add this line to your application's Gemfile:

gem 'quick_random_records'

And then execute:

$ bundle

Or install it yourself as:

$ gem install quick_random_records

# return ActiveRecord::Relation contains 10 random model objects from User Table

users = User.random_records(10)

Scenario: query 100 random records from table with 550,000 data rows in localhost.

1. quick_random_records costs only 6.2ms totally.
2. Model.order("RAND()").limit(num) costs 3314.1ms.
3. Model.where(id: Model.pluck(:id).sample(num)) costs 1659.4ms totally.

This strategy is fast because:

(1) Instead of plucking all id in the table, it selects id bewteen min_id and max_id. Then make further query to make complement if there is not enough valid records in the previous query. (PS: it won't select the duplicate records.)

(2) It selects 1.05 times more records per query than you require, so that it doesn't need to perform further query to
make complements for insufficient valid records. You can configure your own multiply factor, which is 1.05 by default.

# select 1.1 times more than required, that is 110 in this case. 
# And it will truncate to 100 before method return.
   
users = User.random_records(100, multiply: 1.1) 

This strategy works extremely well with table that has a lot of records and few deleted records.

However, for tables with lots of deleted records (ex: There is 8 deleted records among 10 records), it may return fewer records than you require because it limit the loop of making query of complements to avoid infinite loop.

The default loop_limit is 3 times. You can configure your own loop_limit for searching complements if there is not enough valid records in the previous query.

users = User.random_records(100, loop_limit: 5)

After checking out the repo, run bin/setup to install dependencies. Then, run rake test 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.

Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/quick_random_records. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

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