Question

I’m currently hacking on an events site and have never had a problem optimizing queries/scaling my db in the past as there was never that much data, but now there’s almost a million rows in the db and it’s taking ~15,000 m/s to render a feed of events, in particular the partial (within each _event.html.erb) that’s really slow is where all the users that youre currently following that are attending that event are displayed. I’ve looked up a lot of possibilities to improve performance including eager loading, indexing, memcache, etc…but was wondering how this can be rewritten to perform faster? Thank you!

_attending.html.erb

<% if user_signed_in? %>
        <% @rsvp = Rsvp.where(:voter_id => current_user.following, :event_id => event.id, :status => 'going') %>
        <% if @rsvp.count == 0 %>
            <%= eventcount(event) %> going.
        <% elsif @rsvp.count == 1 %>
            <% if eventcount(event) - 1 == 0 %>
                <% Rsvp.where(:voter_id => current_user.following, :event_id => event.id, :status => 'going')[0..0].each do |f| %>
                    <%= link_to User.find(f.voter_id).name, User.find(f.voter_id).slug %> is going.
                <% end %>
            <% else %>
              <% Rsvp.where(:voter_id => current_user.following, :event_id => event.id, :status => 'going')[0..0].each do |f| %>
                  <%= link_to User.find(f.voter_id).name, User.find(f.voter_id).slug %> and <%= eventcount(event) - 1 %> going.
              <% end %>
            <% end %>
        <% elsif @rsvp.count == 2 %>
            <% if eventcount(event) - 2 == 0 %>
                <% Rsvp.where(:voter_id => current_user.following, :event_id => event.id, :status => 'going')[0..0].each do |f| %>
                    <%= link_to User.find(f.voter_id).name, User.find(f.voter_id).slug %> and
                <% end %>
                <% Rsvp.where(:voter_id => current_user.following, :event_id => event.id, :status => 'going')[1..1].each do |f| %>
                    <%= link_to User.find(f.voter_id).name, User.find(f.voter_id).slug %> are going.
                <% end %>
            <% else %>
              <% Rsvp.where(:voter_id => current_user.following, :event_id => event.id, :status => 'going')[0..0].each do |f| %>
                  <%= link_to User.find(f.voter_id).name, User.find(f.voter_id).slug %>,
              <% end %>
              <% Rsvp.where(:voter_id => current_user.following, :event_id => event.id, :status => 'going')[1..1].each do |f| %>
                  <%= link_to User.find(f.voter_id).name, User.find(f.voter_id).slug %> and <%= eventcount(event) - 2 %> going.
              <% end %>
                <% end %>
        <% elsif @rsvp.count == 3 %>
            <% if eventcount(event) - 3 == 0 %>
                <% Rsvp.where(:voter_id => current_user.following, :event_id => event.id, :status => 'going')[0..0].each do |f| %>
                    <%= link_to User.find(f.voter_id).name, User.find(f.voter_id).slug %>,
                <% end %>
                <% Rsvp.where(:voter_id => current_user.following, :event_id => event.id, :status => 'going')[1..1].each do |f| %>
                    <%= link_to User.find(f.voter_id).name, User.find(f.voter_id).slug %>, and
                <% end %>
                <% Rsvp.where(:voter_id => current_user.following, :event_id => event.id, :status => 'going')[2..2].each do |f| %>
                    <%= link_to User.find(f.voter_id).name, User.find(f.voter_id).slug %> are going.
                <% end %>
            <% else %>
              <% Rsvp.where(:voter_id => current_user.following, :event_id => event.id, :status => 'going')[0..0].each do |f| %>
                  <%= link_to User.find(f.voter_id).name, User.find(f.voter_id).slug %>,
              <% end %>
              <% Rsvp.where(:voter_id => current_user.following, :event_id => event.id, :status => 'going')[1..1].each do |f| %>
                  <%= link_to User.find(f.voter_id).name, User.find(f.voter_id).slug %>,
              <% end %>
              <% Rsvp.where(:voter_id => current_user.following, :event_id => event.id, :status => 'going')[2..2].each do |f| %>
                  <%= link_to User.find(f.voter_id).name, User.find(f.voter_id).slug %> and <%= eventcount(event) - 3 %> are going.
              <% end %>
            <% end %>
            <% end %>
    <% else %>
        <%= eventcount(event) %> going.
    <% end %>

Schema for RSVP

create_table "rsvps", :force => true do |t|
  t.string    "status"
  t.integer   "event_id"
  t.integer   "voter_id"
  t.string    "voter_name"
  t.string    "voter_type"
  t.timestamp "created_at", :null => false
  t.timestamp "updated_at", :null => false
end

add_index "rsvps", ["voter_id", "voter_type", "event_id"], :name => "fk_one_rsvp_per_user_per_entity", :unique => true
add_index "rsvps", ["voter_id", "voter_type"], :name => "index_rsvps_on_voter_id_and_voter_type"

Schema for Relationship

create_table "relationships", :force => true do |t|
  t.integer   "follower_id"
  t.integer   "followed_id"
  t.timestamp "created_at",  :null => false
  t.timestamp "updated_at",  :null => false
end

add_index "relationships", ["followed_id"], :name => "index_relationships_on_followed_id"
add_index "relationships", ["follower_id"], :name => "index_relationships_on_follower_id"

Relevant part of User model

has_many :relationships, :foreign_key => "follower_id",
:dependent => :destroy

has_many :following, :through => :relationships, :source => :followed

has_many :reverse_relationships, :foreign_key => "followed_id",
       :class_name => "Relationship",
       :dependent => :destroy
has_many :followers, :through => :reverse_relationships, :source => :follower

Answer 1

If the large db is the RSVP:

You do a very large call to the db in your partial, try to reduce the n call Rsvp.where(:voter_id => current_user.following, :event_id => event.id, :status => 'going') only one time, and then working on it in the different cases. This can help a little in performance (every time you call a .where in large db is a complex process if you have a large db). Re-use the variable @rsvp.