Merge branch '14508-multi-store' into 'master'

Implement MultiStore with fallback mechanism

See merge request gitlab-org/gitlab!73660

config/feature_flags/development/use_multi_store.yml

+---
+name: use_multi_store
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/73660
+rollout_issue_url:
+milestone: '14.5'
+type: development
+group: group::memory
+default_enabled: false

lib/gitlab/redis/multi_store.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Redis
+    class MultiStore
+      include Gitlab::Utils::StrongMemoize
+
+      class ReadFromPrimaryError < StandardError
+        def message
+          'Value not found on the redis primary store. Read from the redis secondary store successful.'
+        end
+      end
+      class MethodMissingError < StandardError
+        def message
+          'Method missing. Falling back to execute method on the redis secondary store.'
+        end
+      end
+
+      attr_reader :primary_store, :secondary_store, :instance_name
+
+      FAILED_TO_READ_ERROR_MESSAGE = 'Failed to read from the redis primary_store.'
+      FAILED_TO_WRITE_ERROR_MESSAGE = 'Failed to write to the redis primary_store.'
+
+      READ_COMMANDS = %i(
+        get
+        mget
+        smembers
+        scard
+      ).freeze
+
+      WRITE_COMMANDS = %i(
+        set
+        setnx
+        setex
+        sadd
+        srem
+        del
+        pipelined
+        flushdb
+      ).freeze
+
+      def initialize(primary_store, secondary_store, instance_name = nil)
+        @primary_store = primary_store
+        @secondary_store = secondary_store
+        @instance_name = instance_name
+
+        validate_stores!
+      end
+
+      READ_COMMANDS.each do |name|
+        define_method(name) do |*args, &block|
+          if multi_store_enabled?
+            read_command(name, *args, &block)
+          else
+            secondary_store.send(name, *args, &block) # rubocop:disable GitlabSecurity/PublicSend
+          end
+        end
+      end
+
+      WRITE_COMMANDS.each do |name|
+        define_method(name) do |*args, &block|
+          if multi_store_enabled?
+            write_command(name, *args, &block)
+          else
+            secondary_store.send(name, *args, &block) # rubocop:disable GitlabSecurity/PublicSend
+          end
+        end
+      end
+
+      def method_missing(...)
+        return @instance.send(...) if @instance # rubocop:disable GitlabSecurity/PublicSend
+
+        log_method_missing(...)
+
+        secondary_store.send(...) # rubocop:disable GitlabSecurity/PublicSend
+      end
+
+      def respond_to_missing?(command_name, include_private = false)
+        true
+      end
+
+      # This is needed because of Redis::Rack::Connection is requiring Redis::Store
+      # https://github.com/redis-store/redis-rack/blob/a833086ba494083b6a384a1a4e58b36573a9165d/lib/redis/rack/connection.rb#L15
+      # Done similarly in https://github.com/lsegal/yard/blob/main/lib/yard/templates/template.rb#L122
+      def is_a?(klass)
+        return true if klass == secondary_store.class
+
+        super(klass)
+      end
+      alias_method :kind_of?, :is_a?
+
+      def to_s
+        if multi_store_enabled?
+          primary_store.to_s
+        else
+          secondary_store.to_s
+        end
+      end
+
+      private
+
+      def log_method_missing(command_name, *_args)
+        log_error(MethodMissingError.new, command_name)
+        increment_method_missing_count(command_name)
+      end
+
+      def read_command(command_name, *args, &block)
+        if @instance
+          send_command(@instance, command_name, *args, &block)
+        else
+          read_one_with_fallback(command_name, *args, &block)
+        end
+      end
+
+      def write_command(command_name, *args, &block)
+        if @instance
+          send_command(@instance, command_name, *args, &block)
+        else
+          write_both(command_name, *args, &block)
+        end
+      end
+
+      def read_one_with_fallback(command_name, *args, &block)
+        begin
+          value = send_command(primary_store, command_name, *args, &block)
+        rescue StandardError => e
+          log_error(e, command_name,
+            multi_store_error_message: FAILED_TO_READ_ERROR_MESSAGE)
+        end
+
+        value ||= fallback_read(command_name, *args, &block)
+
+        value
+      end
+
+      def fallback_read(command_name, *args, &block)
+        value = send_command(secondary_store, command_name, *args, &block)
+
+        if value
+          log_error(ReadFromPrimaryError.new, command_name)
+          increment_read_fallback_count(command_name)
+        end
+
+        value
+      end
+
+      def write_both(command_name, *args, &block)
+        begin
+          send_command(primary_store, command_name, *args, &block)
+        rescue StandardError => e
+          log_error(e, command_name,
+            multi_store_error_message: FAILED_TO_WRITE_ERROR_MESSAGE)
+        end
+
+        send_command(secondary_store, command_name, *args, &block)
+      end
+
+      def multi_store_enabled?
+        Feature.enabled?(:use_multi_store, default_enabled: :yaml) && !same_redis_store?
+      end
+
+      def same_redis_store?
+        strong_memoize(:same_redis_store) do
+          # <Redis client v4.4.0 for redis:///path_to/redis/redis.socket/5>"
+          primary_store.inspect == secondary_store.inspect
+        end
+      end
+
+      # rubocop:disable GitlabSecurity/PublicSend
+      def send_command(redis_instance, command_name, *args, &block)
+        if block_given?
+          # Make sure that block is wrapped and executed only on the redis instance that is executing the block
+          redis_instance.send(command_name, *args) do |*params|
+            with_instance(redis_instance, *params, &block)
+          end
+        else
+          redis_instance.send(command_name, *args)
+        end
+      end
+      # rubocop:enable GitlabSecurity/PublicSend
+
+      def with_instance(instance, *params)
+        @instance = instance
+
+        yield(*params)
+      ensure
+        @instance = nil
+      end
+
+      def increment_read_fallback_count(command_name)
+        @read_fallback_counter ||= Gitlab::Metrics.counter(:gitlab_redis_multi_store_read_fallback_total, 'Client side Redis MultiStore reading fallback')
+        @read_fallback_counter.increment(command: command_name, instance_name: instance_name)
+      end
+
+      def increment_method_missing_count(command_name)
+        @method_missing_counter ||= Gitlab::Metrics.counter(:gitlab_redis_multi_store_method_missing_total, 'Client side Redis MultiStore method missing')
+        @method_missing_counter.increment(command: command_name, innamece_name: instance_name)
+      end
+
+      def validate_stores!
+        raise ArgumentError, 'primary_store is required' unless primary_store
+        raise ArgumentError, 'secondary_store is required' unless secondary_store
+        raise ArgumentError, 'invalid primary_store' unless primary_store.is_a?(::Redis)
+        raise ArgumentError, 'invalid secondary_store' unless secondary_store.is_a?(::Redis)
+      end
+
+      def log_error(exception, command_name, extra = {})
+        Gitlab::ErrorTracking.log_exception(
+          exception,
+          command_name: command_name,
+          extra: extra.merge(instance_name: instance_name))
+      end
+    end
+  end
+end

spec/lib/gitlab/redis/multi_store_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Redis::MultiStore do
+  using RSpec::Parameterized::TableSyntax
+
+  let_it_be(:redis_store_class) do
+    Class.new(Gitlab::Redis::Wrapper) do
+      def config_file_name
+        config_file_name = "spec/fixtures/config/redis_new_format_host.yml"
+        Rails.root.join(config_file_name).to_s
+      end
+
+      def self.name
+        'Sessions'
+      end
+    end
+  end
+
+  let_it_be(:primary_db) { 1 }
+  let_it_be(:secondary_db) { 2 }
+  let_it_be(:primary_store) { create_redis_store(redis_store_class.params, db: primary_db, serializer: nil) }
+  let_it_be(:secondary_store) { create_redis_store(redis_store_class.params, db: secondary_db, serializer: nil) }
+  let_it_be(:instance_name) { 'TestStore' }
+  let_it_be(:multi_store) { described_class.new(primary_store, secondary_store, instance_name)}
+
+  subject { multi_store.send(name, *args) }
+
+  after(:all) do
+    primary_store.flushdb
+    secondary_store.flushdb
+  end
+
+  context 'when primary_store is nil' do
+    let(:multi_store) { described_class.new(nil, secondary_store, instance_name)}
+
+    it 'fails with exception' do
+      expect { multi_store }.to raise_error(ArgumentError, /primary_store is required/)
+    end
+  end
+
+  context 'when secondary_store is nil' do
+    let(:multi_store) { described_class.new(primary_store, nil, instance_name)}
+
+    it 'fails with exception' do
+      expect { multi_store }.to raise_error(ArgumentError, /secondary_store is required/)
+    end
+  end
+
+  context 'when primary_store is not a ::Redis instance' do
+    before do
+      allow(primary_store).to receive(:is_a?).with(::Redis).and_return(false)
+    end
+
+    it 'fails with exception' do
+      expect { described_class.new(primary_store, secondary_store, instance_name) }.to raise_error(ArgumentError, /invalid primary_store/)
+    end
+  end
+
+  context 'when secondary_store is not a ::Redis instance' do
+    before do
+      allow(secondary_store).to receive(:is_a?).with(::Redis).and_return(false)
+    end
+
+    it 'fails with exception' do
+      expect { described_class.new(primary_store, secondary_store, instance_name) }.to raise_error(ArgumentError, /invalid secondary_store/)
+    end
+  end
+
+  context 'with READ redis commands' do
+    let_it_be(:key1) { "redis:{1}:key_a" }
+    let_it_be(:key2) { "redis:{1}:key_b" }
+    let_it_be(:value1) { "redis_value1"}
+    let_it_be(:value2) { "redis_value2"}
+    let_it_be(:skey) { "redis:set:key" }
+    let_it_be(:keys) { [key1, key2] }
+    let_it_be(:values) { [value1, value2] }
+    let_it_be(:svalues) { [value2, value1] }
+
+    where(:case_name, :name, :args, :value, :block) do
+      'execute :get command'      | :get      | ref(:key1)  | ref(:value1)  | nil
+      'execute :mget command'     | :mget     | ref(:keys)  | ref(:values)  | nil
+      'execute :mget with block'  | :mget     | ref(:keys)  | ref(:values)  | ->(value) { value }
+      'execute :smembers command' | :smembers | ref(:skey)  | ref(:svalues) | nil
+      'execute :scard command'    | :scard    | ref(:skey)  | 2             | nil
+    end
+
+    before(:all) do
+      primary_store.multi do |multi|
+        multi.set(key1, value1)
+        multi.set(key2, value2)
+        multi.sadd(skey, value1)
+        multi.sadd(skey, value2)
+      end
+
+      secondary_store.multi do |multi|
+        multi.set(key1, value1)
+        multi.set(key2, value2)
+        multi.sadd(skey, value1)
+        multi.sadd(skey, value2)
+      end
+    end
+
+    RSpec.shared_examples_for 'reads correct value' do
+      it 'returns the correct value' do
+        if value.is_a?(Array)
+          # :smembers does not guarantee the order it will return the values (unsorted set)
+          is_expected.to match_array(value)
+        else
+          is_expected.to eq(value)
+        end
+      end
+    end
+
+    RSpec.shared_examples_for 'fallback read from the secondary store' do
+      it 'fallback and execute on secondary instance' do
+        expect(secondary_store).to receive(name).with(*args).and_call_original
+
+        subject
+      end
+
+      it 'logs the ReadFromPrimaryError' do
+        expect(Gitlab::ErrorTracking).to receive(:log_exception).with(an_instance_of(Gitlab::Redis::MultiStore::ReadFromPrimaryError),
+          hash_including(command_name: name, extra: hash_including(instance_name: instance_name)))
+
+        subject
+      end
+
+      it 'increment read fallback count metrics' do
+        expect(multi_store).to receive(:increment_read_fallback_count).with(name)
+
+        subject
+      end
+
+      include_examples 'reads correct value'
+
+      context 'when fallback read from the secondary instance raises an exception' do
+        before do
+          allow(secondary_store).to receive(name).with(*args).and_raise(StandardError)
+        end
+
+        it 'fails with exception' do
+          expect { subject }.to raise_error(StandardError)
+        end
+      end
+    end
+
+    RSpec.shared_examples_for 'secondary store' do
+      it 'execute on the secondary instance' do
+        expect(secondary_store).to receive(name).with(*args).and_call_original
+
+        subject
+      end
+
+      include_examples 'reads correct value'
+
+      it 'does not execute on the primary store' do
+        expect(primary_store).not_to receive(name)
+
+        subject
+      end
+    end
+
+    with_them do
+      describe "#{name}" do
+        before do
+          allow(primary_store).to receive(name).and_call_original
+          allow(secondary_store).to receive(name).and_call_original
+        end
+
+        context 'with feature flag :use_multi_store enabled' do
+          before do
+            stub_feature_flags(use_multi_store: true)
+          end
+
+          context 'when reading from the primary is successful' do
+            it 'returns the correct value' do
+              expect(primary_store).to receive(name).with(*args).and_call_original
+
+              subject
+            end
+
+            it 'does not execute on the secondary store' do
+              expect(secondary_store).not_to receive(name)
+
+              subject
+            end
+
+            include_examples 'reads correct value'
+          end
+
+          context 'when reading from primary instance is raising an exception' do
+            before do
+              allow(primary_store).to receive(name).with(*args).and_raise(StandardError)
+              allow(Gitlab::ErrorTracking).to receive(:log_exception)
+            end
+
+            it 'logs the exception' do
+              expect(Gitlab::ErrorTracking).to receive(:log_exception).with(an_instance_of(StandardError),
+                hash_including(extra: hash_including(:multi_store_error_message, instance_name: instance_name),
+                               command_name: name))
+
+              subject
+            end
+
+            include_examples 'fallback read from the secondary store'
+          end
+
+          context 'when reading from primary instance return no value' do
+            before do
+              allow(primary_store).to receive(name).and_return(nil)
+            end
+
+            include_examples 'fallback read from the secondary store'
+          end
+
+          context 'when the command is executed within pipelined block' do
+            subject do
+              multi_store.pipelined do
+                multi_store.send(name, *args)
+              end
+            end
+
+            it 'is executed only 1 time on primary instance' do
+              expect(primary_store).to receive(name).with(*args).once
+
+              subject
+            end
+          end
+
+          if params[:block]
+            subject do
+              multi_store.send(name, *args, &block)
+            end
+
+            context 'when block is provided' do
+              it 'yields to the block' do
+                expect(primary_store).to receive(name).and_yield(value)
+
+                subject
+              end
+
+              include_examples 'reads correct value'
+            end
+          end
+        end
+
+        context 'with feature flag :use_multi_store is disabled' do
+          before do
+            stub_feature_flags(use_multi_store: false)
+          end
+
+          it_behaves_like 'secondary store'
+        end
+
+        context 'with both primary and secondary store using same redis instance' do
+          let(:primary_store) { create_redis_store(redis_store_class.params, db: primary_db, serializer: nil) }
+          let(:secondary_store) { create_redis_store(redis_store_class.params, db: primary_db, serializer: nil) }
+          let(:multi_store) { described_class.new(primary_store, secondary_store, instance_name)}
+
+          it_behaves_like 'secondary store'
+        end
+      end
+    end
+  end
+
+  context 'with WRITE redis commands' do
+    let_it_be(:key1) { "redis:{1}:key_a" }
+    let_it_be(:key2) { "redis:{1}:key_b" }
+    let_it_be(:value1) { "redis_value1"}
+    let_it_be(:value2) { "redis_value2"}
+    let_it_be(:key1_value1) { [key1, value1] }
+    let_it_be(:key1_value2) { [key1, value2] }
+    let_it_be(:ttl) { 10 }
+    let_it_be(:key1_ttl_value1) { [key1, ttl, value1] }
+    let_it_be(:skey) { "redis:set:key" }
+    let_it_be(:svalues1) { [value2, value1] }
+    let_it_be(:svalues2) { [value1] }
+    let_it_be(:skey_value1) { [skey, value1] }
+    let_it_be(:skey_value2) { [skey, value2] }
+
+    where(:case_name, :name, :args, :expected_value, :verification_name, :verification_args) do
+      'execute :set command'       | :set      | ref(:key1_value1)      | ref(:value1)      | :get      | ref(:key1)
+      'execute :setnx command'     | :setnx    | ref(:key1_value2)      | ref(:value1)      | :get      | ref(:key2)
+      'execute :setex command'     | :setex    | ref(:key1_ttl_value1)  | ref(:ttl)         | :ttl      | ref(:key1)
+      'execute :sadd command'      | :sadd     | ref(:skey_value2)      | ref(:svalues1)    | :smembers | ref(:skey)
+      'execute :srem command'      | :srem     | ref(:skey_value1)      | []                | :smembers | ref(:skey)
+      'execute :del command'       | :del      | ref(:key2)             | nil               | :get      | ref(:key2)
+      'execute :flushdb command'   | :flushdb  | nil                    | 0                 | :dbsize   | nil
+    end
+
+    before do
+      primary_store.flushdb
+      secondary_store.flushdb
+
+      primary_store.multi do |multi|
+        multi.set(key2, value1)
+        multi.sadd(skey, value1)
+      end
+
+      secondary_store.multi do |multi|
+        multi.set(key2, value1)
+        multi.sadd(skey, value1)
+      end
+    end
+
+    RSpec.shared_examples_for 'verify that store contains values' do |store|
+      it "#{store} redis store contains correct values", :aggregate_errors do
+        subject
+
+        redis_store = multi_store.send(store)
+
+        if expected_value.is_a?(Array)
+          # :smembers does not guarantee the order it will return the values
+          expect(redis_store.send(verification_name, *verification_args)).to match_array(expected_value)
+        else
+          expect(redis_store.send(verification_name, *verification_args)).to eq(expected_value)
+        end
+      end
+    end
+
+    with_them do
+      describe "#{name}" do
+        let(:expected_args) {args || no_args }
+
+        before do
+          allow(primary_store).to receive(name).and_call_original
+          allow(secondary_store).to receive(name).and_call_original
+        end
+
+        context 'with feature flag :use_multi_store enabled' do
+          before do
+            stub_feature_flags(use_multi_store: true)
+          end
+
+          context 'when executing on primary instance is successful' do
+            it 'executes on both primary and secondary redis store', :aggregate_errors do
+              expect(primary_store).to receive(name).with(*expected_args).and_call_original
+              expect(secondary_store).to receive(name).with(*expected_args).and_call_original
+
+              subject
+            end
+
+            include_examples 'verify that store contains values', :primary_store
+            include_examples 'verify that store contains values', :secondary_store
+          end
+
+          context 'when executing on the primary instance is raising an exception' do
+            before do
+              allow(primary_store).to receive(name).with(*expected_args).and_raise(StandardError)
+              allow(Gitlab::ErrorTracking).to receive(:log_exception)
+            end
+
+            it 'logs the exception and execute on secondary instance', :aggregate_errors do
+              expect(Gitlab::ErrorTracking).to receive(:log_exception).with(an_instance_of(StandardError),
+                hash_including(extra: hash_including(:multi_store_error_message), command_name: name))
+              expect(secondary_store).to receive(name).with(*expected_args).and_call_original
+
+              subject
+            end
+
+            include_examples 'verify that store contains values', :secondary_store
+          end
+
+          context 'when the command is executed within pipelined block' do
+            subject do
+              multi_store.pipelined do
+                multi_store.send(name, *args)
+              end
+            end
+
+            it 'is executed only 1 time on each instance', :aggregate_errors do
+              expect(primary_store).to receive(name).with(*expected_args).once
+              expect(secondary_store).to receive(name).with(*expected_args).once
+
+              subject
+            end
+
+            include_examples 'verify that store contains values', :primary_store
+            include_examples 'verify that store contains values', :secondary_store
+          end
+        end
+
+        context 'with feature flag :use_multi_store is disabled' do
+          before do
+            stub_feature_flags(use_multi_store: false)
+          end
+
+          it 'executes only on the secondary redis store', :aggregate_errors do
+            expect(secondary_store).to receive(name).with(*expected_args)
+            expect(primary_store).not_to receive(name).with(*expected_args)
+
+            subject
+          end
+
+          include_examples 'verify that store contains values', :secondary_store
+        end
+      end
+    end
+  end
+
+  context 'with unsupported command' do
+    before do
+      primary_store.flushdb
+      secondary_store.flushdb
+    end
+
+    let_it_be(:key) { "redis:counter" }
+
+    subject do
+      multi_store.incr(key)
+    end
+
+    it 'executes method missing' do
+      expect(multi_store).to receive(:method_missing)
+
+      subject
+    end
+
+    it 'logs MethodMissingError' do
+      expect(Gitlab::ErrorTracking).to receive(:log_exception).with(an_instance_of(Gitlab::Redis::MultiStore::MethodMissingError),
+        hash_including(command_name: :incr, extra: hash_including(instance_name: instance_name)))
+
+      subject
+    end
+
+    it 'increments method missing counter' do
+      expect(multi_store).to receive(:increment_method_missing_count).with(:incr)
+
+      subject
+    end
+
+    it 'fallback and executes only on the secondary store', :aggregate_errors do
+      expect(secondary_store).to receive(:incr).with(key).and_call_original
+      expect(primary_store).not_to receive(:incr)
+
+      subject
+    end
+
+    it 'correct value is stored on the secondary store', :aggregate_errors do
+      subject
+
+      expect(primary_store.get(key)).to be_nil
+      expect(secondary_store.get(key)).to eq('1')
+    end
+
+    context 'when the command is executed within pipelined block' do
+      subject do
+        multi_store.pipelined do
+          multi_store.incr(key)
+        end
+      end
+
+      it 'is executed only 1 time on each instance', :aggregate_errors do
+        expect(primary_store).to receive(:incr).with(key).once
+        expect(secondary_store).to receive(:incr).with(key).once
+
+        subject
+      end
+
+      it "both redis stores are containing correct values", :aggregate_errors do
+        subject
+
+        expect(primary_store.get(key)).to eq('1')
+        expect(secondary_store.get(key)).to eq('1')
+      end
+    end
+  end
+
+  def create_redis_store(options, extras = {})
+    ::Redis::Store.new(options.merge(extras))
+  end
+end