PERF: exact email match bypass

instead of scanning full table when there is an exact email match ONLY
return the actual user.

lib/admin_user_index_query.rb

@@ -101,13 +101,26 @@ class AdminUserIndexQuery
     end
   end
 
+  def filter_by_user_with_bypass(filter)
+    if filter =~ /.+@.+/
+      # probably an email so try the bypass
+      user_id = UserEmail.where(email: filter.downcase).pluck(:user_id).first
+      if user_id
+        return @query.where('users.id = ?', user_id)
+      end
+    end
+
+    @query.where('username_lower ILIKE :filter OR user_emails.email ILIKE :filter', filter: "%#{params[:filter]}%")
+  end
+
   def filter_by_search
-    if params[:filter].present?
-      params[:filter].strip!
-      if ip = IPAddr.new(params[:filter]) rescue nil
+    filter = params[:filter]
+    if filter.present?
+      filter.strip!
+      if ip = IPAddr.new(filter) rescue nil
         @query.where('ip_address <<= :ip OR registration_ip_address <<= :ip', ip: ip.to_cidr_s)
       else
-        @query.where('username_lower ILIKE :filter OR user_emails.email ILIKE :filter', filter: "%#{params[:filter]}%")
+        filter_by_user_with_bypass(filter)
       end
     end
   end

spec/components/admin_user_index_query_spec.rb

@@ -178,6 +178,18 @@ describe AdminUserIndexQuery do
 
   describe "filtering" do
 
+    context "exact email bypass" do
+      it "can correctly bypass expensive ilike query" do
+        user = Fabricate(:user, email: 'sam@Sam.com')
+
+        query = AdminUserIndexQuery.new(filter: 'Sam@sam.com').find_users_query
+        expect(query.count).to eq(1)
+        expect(query.first.id).to eq(user.id)
+
+        expect(query.to_sql.downcase).not_to include("ilike")
+      end
+    end
+
     context "by email fragment" do
 
       before(:each) { Fabricate(:user, email: "test1@example.com") }