This gem adds slotted counters support to Active Record counter cache. Slotted counters help to reduce contention on a single row update in case you have many concurrent operations (like updating a page views counter during traffic spikes).

Read more about slotted counters in this post.

Add to your project:

# Gemfile
gem "activerecord-slotted_counters"

• Ruby (MRI) >= 2.7.0

First, add and apply the required migration(-s):

bin/rails generate slotted_counters:install
bin/rails db:migrate

Then, add the following line to the model to add a slotted counter:

class User < ApplicationRecord
  has_slotted_counter :comments
end

Now you can use all the common counter cache APIs as before:

# Manipulating the counter explicitly
user = User.first

User.increment_counter(:comments_count, user.id)
User.decrement_counter(:comments_count, user.id)
User.reset_counters(user.id, :comments)
# etc.

# Reading the value
user.comments_count

Under the hood, a row in the slotted_counters table is created associated with the record.

NOTE: Reading the current value performs SQL query once:

user.comments_count #=> select * from slotted_counters where ...
user.comments_count #=> no sql

If you want to preload counters for multiple records, you can use a convenient #with_slotted_counters method:

User.all.with_slotted_counters(:comments).find_each do
  _1.comments_count #=> no sql
end

Using counter_cache: true on belongs_to associations also works as expected.

• Gem supports only PostgreSQL for Rails 6

Bug reports and pull requests are welcome on GitHub at https://github.com/evilmartians/activerecord-slotted_counters.

This gem is generated via new-gem-generator.

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