load-records-in-batches-with-find-each.md

Load Records In Batches With find_each

The base enumerable method offered by Ruby is #each. If you need to interact with an array of elements, that's a method you'll reach for at some point.

When working with an ActiveRecord collection in Rails, you should use the #find_each method instead of #each. That's because under the hood it batches the records that it will load in 1000 at a time. This is important to keep your server's resource usage from exploding when requesting a ton of records.

Consider a users table that contains 10,000 records that are active.

User.where(active: true).each do |user|
  # do something
end

With #each, all 10,000 records will be loaded into memory at once as ActiveRecord objects. That's potentially a lot of load on the server's available memory. Then imagine the table contains 100,000 or 1,000,000 records. This can become a big problem.

User.where(active: true).find_each do |user|
  # do something
end

With #find_each, which uses #find_in_batches under the hood, only 1000 ActiveRecord objects get loaded into memory at a time.

If you want to exercise more control over the batching, you can use #find_in_batches directly.