A memory saving alternative to Active::Record's find_in_batches and find_each methods that spreads queries with large result sets into smaller manageable subsets while allowing you to set a sort order. This saves an enormous amount of memory / RAM when handling large queries (1000+), especially those that can grow over time.

This gem is safe for concurrent inserts / deletes from the database as you query your model. It is guaranteed not to return duplicates as long as you have follow ActiveRecord's conventions of having a unique id primary key column.

Add this line to your application's Gemfile:

gem 'batched_query'

And then execute:

$ bundle

Or install it yourself as:

$ gem install batched_query

You may either loop through ActiveRecord results using BatchedQuery::Runner.each_set(query, &block) like so:

# Any ActiveRecord query
cars = Car.where("brand_name = 'Ferrari'").order("created_at desc")

# Set the limit of each subquery
BatchedQuery::Runner.limit = 100
BatchedQuery::Runner.each_set(cars) do |batch_of_cars|
  # process results in manageable subsets
  batch_of_cars.map { |car| ... }
end

Or you may loop through all the results using BatchedQuery::Runner.each_result(query, &block) like so:

BatchedQuery::Runner.limit = 200
BatchedQuery::Runner.each_result(cars) do |car|
  # access each car as if you loaded all of the records at once
  car.start!
end

By default, if you don't set the limit explicitly, it will default to 500 results per query.

Note: If you are using any includes(...) methods the total amount of objects loaded will double and the limit that you set will only apply to the model you are running a query on.

One limitation of this implementation is that you will not be able to use "select" or "pluck" statements in your query. However, those statements generally take a lot less memory because you are loading an array of strings / integers instead of full ActiveRecord objects.

1. Fork it ( http://github.com//batched_query/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request