diff --git a/app/services/users/activity_service.rb b/app/services/users/activity_service.rb
index 483821b7f01..facf21a7f5c 100644
--- a/app/services/users/activity_service.rb
+++ b/app/services/users/activity_service.rb
@@ -14,7 +14,7 @@ module Users
     private
 
     def record_activity
-      @author.record_activity
+      Gitlab::UserActivities.record(@author.id)
 
       Rails.logger.debug("Recorded activity: #{@activity} for User ID: #{@author.id} (username: #{@author.username}")
     end
diff --git a/lib/gitlab/user_activities.rb b/lib/gitlab/user_activities.rb
new file mode 100644
index 00000000000..eb36ab9fded
--- /dev/null
+++ b/lib/gitlab/user_activities.rb
@@ -0,0 +1,34 @@
+module Gitlab
+  class UserActivities
+    include Enumerable
+
+    KEY = 'users:activities'.freeze
+    BATCH_SIZE = 500
+
+    def self.record(key, time = Time.now)
+      Gitlab::Redis.with do |redis|
+        redis.hset(KEY, key, time.to_i)
+      end
+    end
+
+    def delete(*keys)
+      Gitlab::Redis.with do |redis|
+        redis.hdel(KEY, keys)
+      end
+    end
+
+    def each
+      cursor = 0
+      loop do
+        cursor, pairs =
+          Gitlab::Redis.with do |redis|
+            redis.hscan(KEY, cursor, count: BATCH_SIZE)
+          end
+
+        Hash[pairs].each { |pair| yield pair }
+
+        break if cursor == '0'
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/user_activities/activity.rb b/lib/gitlab/user_activities/activity.rb
deleted file mode 100644
index ec052870ee3..00000000000
--- a/lib/gitlab/user_activities/activity.rb
+++ /dev/null
@@ -1,16 +0,0 @@
-module Gitlab
-  module UserActivities
-    class Activity
-      attr_reader :username
-
-      def initialize(username, time)
-        @username = username
-        @time = time
-      end
-
-      def last_activity_at
-        @last_activity_at ||= Time.at(@time).to_s(:db)
-      end
-    end
-  end
-end
diff --git a/lib/gitlab/user_activities/activity_set.rb b/lib/gitlab/user_activities/activity_set.rb
deleted file mode 100644
index 6b8e540e99b..00000000000
--- a/lib/gitlab/user_activities/activity_set.rb
+++ /dev/null
@@ -1,67 +0,0 @@
-module Gitlab
-  module UserActivities
-    class ActivitySet
-      delegate :total_count,
-               :total_pages,
-               :current_page,
-               :limit_value,
-               :first_page?,
-               :prev_page,
-               :last_page?,
-               :next_page, to: :pagination_delegate
-
-      KEY = 'user/activities'
-
-      def self.record(user)
-        Gitlab::Redis.with do |redis|
-          redis.zadd(KEY, Time.now.to_i, user.username)
-        end
-      end
-
-      def initialize(from: nil, page: nil, per_page: nil)
-        @from = sanitize_date(from)
-        @to = Time.now.to_i
-        @page = page
-        @per_page = per_page
-      end
-
-      def activities
-        @activities ||= raw_activities.map { |activity| Activity.new(*activity) }
-      end
-
-      private
-
-      def sanitize_date(date)
-        Time.strptime(date, "%Y-%m-%d").to_i
-      rescue TypeError, ArgumentError
-        default_from
-      end
-
-      def pagination_delegate
-        @pagination_delegate ||= Gitlab::PaginationDelegate.new(page: @page,
-                                                                per_page: @per_page,
-                                                                count: count)
-      end
-
-      def raw_activities
-        Gitlab::Redis.with do |redis|
-          redis.zrangebyscore(KEY, @from, @to, with_scores: true, limit: limit)
-        end
-      end
-
-      def count
-        Gitlab::Redis.with do |redis|
-          redis.zcount(KEY, @from, @to)
-        end
-      end
-
-      def limit
-        [pagination_delegate.offset, pagination_delegate.limit_value]
-      end
-
-      def default_from
-        6.months.ago.to_i
-      end
-    end
-  end
-end
diff --git a/spec/controllers/sessions_controller_spec.rb b/spec/controllers/sessions_controller_spec.rb
index d817099394a..038132cffe0 100644
--- a/spec/controllers/sessions_controller_spec.rb
+++ b/spec/controllers/sessions_controller_spec.rb
@@ -43,7 +43,7 @@ describe SessionsController do
         it 'updates the user activity' do
           expect do
             post(:create, user: { login: user.username, password: user.password })
-          end.to change { user_score }.from(0)
+          end.to change { user_activity(user) }
         end
       end
     end
diff --git a/spec/lib/gitlab/user_activities/activity_set_spec.rb b/spec/lib/gitlab/user_activities/activity_set_spec.rb
deleted file mode 100644
index 56745bdf0d1..00000000000
--- a/spec/lib/gitlab/user_activities/activity_set_spec.rb
+++ /dev/null
@@ -1,77 +0,0 @@
-require 'spec_helper'
-
-describe Gitlab::UserActivities::ActivitySet, :redis, lib: true do
-  let(:user) { create(:user) }
-
-  it 'shows the last user activity' do
-    Timecop.freeze do
-      user.record_activity
-
-      expect(described_class.new.activities.first).to be_an_instance_of(Gitlab::UserActivities::Activity)
-    end
-  end
-
-  context 'pagination delegation' do
-    let(:pagination_delegate) do
-      Gitlab::PaginationDelegate.new(page: 1,
-                                     per_page: 10,
-                                     count: 20)
-    end
-
-    let(:delegated_methods) { %i[total_count total_pages current_page limit_value first_page? prev_page last_page? next_page] }
-
-    before do
-      allow(described_class.new).to receive(:pagination_delegate).and_return(pagination_delegate)
-    end
-
-    it 'includes the delegated methods' do
-      expect(described_class.new.public_methods).to include(*delegated_methods)
-    end
-  end
-
-  context 'paginated activities' do
-    before do
-      Timecop.scale(3600)
-
-      7.times do
-        create(:user).record_activity
-      end
-    end
-
-    after do
-      Timecop.return
-    end
-
-    it 'shows the 5 oldest user activities paginated' do
-      expect(described_class.new(per_page: 5).activities.count).to eq(5)
-    end
-
-    it 'shows the 2 reamining user activities paginated' do
-      expect(described_class.new(per_page: 5, page: 2).activities.count).to eq(2)
-    end
-
-    it 'shows the oldest first' do
-      activities = described_class.new.activities
-
-      expect(activities.first.last_activity_at).to be < activities.last.last_activity_at
-    end
-  end
-
-  context 'filter by date' do
-    before do
-      create(:user).record_activity
-    end
-
-    it 'shows activities from today' do
-      today = Date.today.to_s("%Y-%m-%d")
-
-      expect(described_class.new(from: today).activities.count).to eq(1)
-    end
-
-    it 'filter activities from tomorrow' do
-      tomorrow = Date.tomorrow.to_s("%Y-%m-%d")
-
-      expect(described_class.new(from: tomorrow).activities.count).to eq(0)
-    end
-  end
-end
diff --git a/spec/lib/gitlab/user_activities/activity_spec.rb b/spec/lib/gitlab/user_activities/activity_spec.rb
deleted file mode 100644
index 6a1150f50c1..00000000000
--- a/spec/lib/gitlab/user_activities/activity_spec.rb
+++ /dev/null
@@ -1,14 +0,0 @@
-require 'spec_helper'
-
-describe Gitlab::UserActivities::Activity, :redis, lib: true do
-  let(:username) { 'user' }
-  let(:activity) { described_class.new('user', Time.new(2016, 12, 12).to_i) }
-
-  it 'has the username' do
-    expect(activity.username).to eq(username)
-  end
-
-  it 'has the last activity at' do
-    expect(activity.last_activity_at).to eq('2016-12-12 00:00:00')
-  end
-end
diff --git a/spec/lib/gitlab/user_activities_spec.rb b/spec/lib/gitlab/user_activities_spec.rb
new file mode 100644
index 00000000000..187d88c8c58
--- /dev/null
+++ b/spec/lib/gitlab/user_activities_spec.rb
@@ -0,0 +1,127 @@
+require 'spec_helper'
+
+describe Gitlab::UserActivities, :redis, lib: true do
+  let(:now) { Time.now }
+
+  describe '.record' do
+    context 'with no time given' do
+      it 'uses Time.now and records an activity in Redis' do
+        Timecop.freeze do
+          now # eager-load now
+          described_class.record(42)
+        end
+
+        Gitlab::Redis.with do |redis|
+          expect(redis.hscan(described_class::KEY, 0)).to eq(['0', [['42', now.to_i.to_s]]])
+        end
+      end
+    end
+
+    context 'with a time given' do
+      it 'uses the given time and records an activity in Redis' do
+        described_class.record(42, now)
+
+        Gitlab::Redis.with do |redis|
+          expect(redis.hscan(described_class::KEY, 0)).to eq(['0', [['42', now.to_i.to_s]]])
+        end
+      end
+    end
+  end
+
+  describe '.delete' do
+    context 'with a single key' do
+      context 'and key exists' do
+        it 'removes the pair from Redis' do
+          described_class.record(42, now)
+
+          Gitlab::Redis.with do |redis|
+            expect(redis.hscan(described_class::KEY, 0)).to eq(['0', [['42', now.to_i.to_s]]])
+          end
+
+          subject.delete(42)
+
+          Gitlab::Redis.with do |redis|
+            expect(redis.hscan(described_class::KEY, 0)).to eq(['0', []])
+          end
+        end
+      end
+
+      context 'and key does not exist' do
+        it 'removes the pair from Redis' do
+          Gitlab::Redis.with do |redis|
+            expect(redis.hscan(described_class::KEY, 0)).to eq(['0', []])
+          end
+
+          subject.delete(42)
+
+          Gitlab::Redis.with do |redis|
+            expect(redis.hscan(described_class::KEY, 0)).to eq(['0', []])
+          end
+        end
+      end
+    end
+
+    context 'with multiple keys' do
+      context 'and all keys exist' do
+        it 'removes the pair from Redis' do
+          described_class.record(41, now)
+          described_class.record(42, now)
+
+          Gitlab::Redis.with do |redis|
+            expect(redis.hscan(described_class::KEY, 0)).to eq(['0', [['41', now.to_i.to_s], ['42', now.to_i.to_s]]])
+          end
+
+          subject.delete(41, 42)
+
+          Gitlab::Redis.with do |redis|
+            expect(redis.hscan(described_class::KEY, 0)).to eq(['0', []])
+          end
+        end
+      end
+
+      context 'and some keys does not exist' do
+        it 'removes the existing pair from Redis' do
+          described_class.record(42, now)
+
+          Gitlab::Redis.with do |redis|
+            expect(redis.hscan(described_class::KEY, 0)).to eq(['0', [['42', now.to_i.to_s]]])
+          end
+
+          subject.delete(41, 42)
+
+          Gitlab::Redis.with do |redis|
+            expect(redis.hscan(described_class::KEY, 0)).to eq(['0', []])
+          end
+        end
+      end
+    end
+  end
+
+  describe 'Enumerable' do
+    before do
+      described_class.record(40, now)
+      described_class.record(41, now)
+      described_class.record(42, now)
+    end
+
+    it 'allows to read the activities sequentially' do
+      expected = { '40' => now.to_i.to_s, '41' => now.to_i.to_s, '42' => now.to_i.to_s }
+
+      actual = described_class.new.each_with_object({}) do |(key, time), actual|
+        actual[key] = time
+      end
+
+      expect(actual).to eq(expected)
+    end
+
+    context 'with many records' do
+      before do
+        1_000.times { |i| described_class.record(i, now) }
+      end
+
+      it 'is possible to loop through all the records' do
+        expect(described_class.new.count).to eq(1_000)
+      end
+    end
+  end
+end
diff --git a/spec/requests/api/internal_spec.rb b/spec/requests/api/internal_spec.rb
index eee8bd51bff..3d6010ede73 100644
--- a/spec/requests/api/internal_spec.rb
+++ b/spec/requests/api/internal_spec.rb
@@ -148,8 +148,6 @@ describe API::Internal, api: true  do
   end
 
   describe "POST /internal/allowed", :redis do
-    include UserActivitiesHelpers
-
     context "access granted" do
       before do
         project.team << [user, :developer]
@@ -183,7 +181,7 @@ describe API::Internal, api: true  do
           expect(response).to have_http_status(200)
           expect(json_response["status"]).to be_truthy
           expect(json_response["repository_path"]).to eq(project.wiki.repository.path_to_repo)
-          expect(user_score).to be_zero
+          expect(user).not_to have_an_activity_record
         end
       end
 
@@ -194,7 +192,7 @@ describe API::Internal, api: true  do
           expect(response).to have_http_status(200)
           expect(json_response["status"]).to be_truthy
           expect(json_response["repository_path"]).to eq(project.wiki.repository.path_to_repo)
-          expect(user_score).not_to be_zero
+          expect(user).to have_an_activity_record
         end
       end
 
@@ -205,7 +203,7 @@ describe API::Internal, api: true  do
           expect(response).to have_http_status(200)
           expect(json_response["status"]).to be_truthy
           expect(json_response["repository_path"]).to eq(project.repository.path_to_repo)
-          expect(user_score).not_to be_zero
+          expect(user).to have_an_activity_record
         end
       end
 
@@ -216,7 +214,7 @@ describe API::Internal, api: true  do
           expect(response).to have_http_status(200)
           expect(json_response["status"]).to be_truthy
           expect(json_response["repository_path"]).to eq(project.repository.path_to_repo)
-          expect(user_score).to be_zero
+          expect(user).not_to have_an_activity_record
         end
 
         context 'project as /namespace/project' do
@@ -252,7 +250,7 @@ describe API::Internal, api: true  do
 
           expect(response).to have_http_status(200)
           expect(json_response["status"]).to be_falsey
-          expect(user_score).to be_zero
+          expect(user).not_to have_an_activity_record
         end
       end
 
@@ -262,7 +260,7 @@ describe API::Internal, api: true  do
 
           expect(response).to have_http_status(200)
           expect(json_response["status"]).to be_falsey
-          expect(user_score).to be_zero
+          expect(user).not_to have_an_activity_record
         end
       end
     end
@@ -280,7 +278,7 @@ describe API::Internal, api: true  do
 
           expect(response).to have_http_status(200)
           expect(json_response["status"]).to be_falsey
-          expect(user_score).to be_zero
+          expect(user).not_to have_an_activity_record
         end
       end
 
@@ -290,7 +288,7 @@ describe API::Internal, api: true  do
 
           expect(response).to have_http_status(200)
           expect(json_response["status"]).to be_falsey
-          expect(user_score).to be_zero
+          expect(user).not_to have_an_activity_record
         end
       end
     end
diff --git a/spec/services/event_create_service_spec.rb b/spec/services/event_create_service_spec.rb
index 13c0aac2363..b06cefe071d 100644
--- a/spec/services/event_create_service_spec.rb
+++ b/spec/services/event_create_service_spec.rb
@@ -122,7 +122,7 @@ describe EventCreateService, services: true do
     end
 
     it 'updates user last activity' do
-      expect { service.push(project, user, {}) }.to change { user_score }
+      expect { service.push(project, user, {}) }.to change { user_activity(user) }
     end
   end
 
diff --git a/spec/services/users/activity_service_spec.rb b/spec/services/users/activity_service_spec.rb
index 07715ad4ca0..8d67ebe3231 100644
--- a/spec/services/users/activity_service_spec.rb
+++ b/spec/services/users/activity_service_spec.rb
@@ -14,18 +14,18 @@ describe Users::ActivityService, services: true do
       end
 
       it 'sets the last activity timestamp for the user' do
-        expect(last_hour_members).to eq([user.username])
+        expect(last_hour_user_ids).to eq([user.id])
       end
 
       it 'updates the same user' do
         service.execute
 
-        expect(last_hour_members).to eq([user.username])
+        expect(last_hour_user_ids).to eq([user.id])
       end
 
       it 'updates the timestamp of an existing user' do
         Timecop.freeze(Date.tomorrow) do
-          expect { service.execute }.to change { user_score }.to(Time.now.to_i)
+          expect { service.execute }.to change { user_activity(user) }.to(Time.now.to_i.to_s)
         end
       end
 
@@ -34,9 +34,15 @@ describe Users::ActivityService, services: true do
           other_user = create(:user)
           described_class.new(other_user, 'type').execute
 
-          expect(last_hour_members).to match_array([user.username, other_user.username])
+          expect(last_hour_user_ids).to match_array([user.id, other_user.id])
         end
       end
     end
   end
+
+  def last_hour_user_ids
+    Gitlab::UserActivities.new.
+      select { |k, v| v >= 1.hour.ago.to_i.to_s }.
+      map { |k, _| k.to_i }
+  end
 end
diff --git a/spec/support/matchers/user_activity_matchers.rb b/spec/support/matchers/user_activity_matchers.rb
new file mode 100644
index 00000000000..ce3b683b6d2
--- /dev/null
+++ b/spec/support/matchers/user_activity_matchers.rb
@@ -0,0 +1,5 @@
+RSpec::Matchers.define :have_an_activity_record do |expected|
+  match do |user|
+    expect(Gitlab::UserActivities.new.find { |k, _| k == user.id.to_s }).to be_present
+  end
+end
diff --git a/spec/support/user_activities_helpers.rb b/spec/support/user_activities_helpers.rb
index ef88dab6c91..f7ca9a31edd 100644
--- a/spec/support/user_activities_helpers.rb
+++ b/spec/support/user_activities_helpers.rb
@@ -1,17 +1,7 @@
 module UserActivitiesHelpers
-  def last_hour_members
-    Gitlab::Redis.with do |redis|
-      redis.zrangebyscore(user_activities_key, 1.hour.ago.to_i, Time.now.to_i)
-    end
-  end
-
-  def user_score
-    Gitlab::Redis.with do |redis|
-      redis.zscore(user_activities_key, user.username).to_i
-    end
-  end
-
-  def user_activities_key
-    'user/activities'
+  def user_activity(user)
+    Gitlab::UserActivities.new.
+      find { |k, _| k == user.id.to_s }&.
+      second
   end
 end