Scaling Search

controller.rb

# in the controller
def index
  # Put the connections in a hash here so it's one DB query
  # instead of 10
  @connections = Hash.new
  User.where(
    id: current_user.cached_connections_ids
  ).each do |user|
    @connections[user.id] = user
  end
end

model_1.rb

def allowed_connections_ids(force = false)
  Rails.cache.fetch("uaci-#{self.id}",
    expires_in: 7.days, 
    force: force
  ) do
    self.allowed_connections.map(&:id)
  end
end

model_2.rb

# This should be run out of band as it's very expensive to compute
def update_allowed_connections_ids(force = false)
  # Cache key is short for 'user connections count'
  Rails.cache.write(
    "uaci-#{self.id}",
    self.allowed_connections.map(&:id),
    force: force
  )
end

# Use this for accessing the allowed ids instead
# of directly accessing it (performance)
def allowed_connections_ids(force = false)
  # If we're forcing, run the expensive computation in-band
  if force
    self.update_allowed_connections_ids(true)
  end
  
  # Try getting the answer from the cache
  cached = Rails.cache.fetch("ucc-#{id}")
  # If we don't have it, schedule and update of this and run 
  # it in the background, and just return 0 for now. 
  if cached.nil?
    cached = 0
    self.delay.update_allowed_connections_ids
  end
  
  cached
end

model_searchable.rb

searchable do
  text :name
  text :location
  integer :id
end

model_searching.rb

def connections_ids_matching(params, force = false)
  # the id set for permission matching must be smaller than 
  # the limitations of solr's OR clause: 1024
  self.allowed_connections_ids.each_slice(1024).flat_map { |id_pool_set|
    User.search_ids do      
      fulltext params[:search_text] do
        boost_fields name: 2, location: 0.5
      end
      with :id, id_pool_set
      paginate per_page: SOLR_MAX_OR_CLAUSES
    end
  }
end

Procfile

web: bundle exec rails server thin -p $PORT
worker: bundle exec rake jobs:work
memcached: bundle exec memcached -m 64
solr: bundle exec rake sunspot:solr:run

view.html.slim

# in the view
ul
  - @connection_ids.each do |connection_id|
    - if connection = @connections[connection_id]
      li= connection.to_s