Swap Repository#merged_branch_names to hash cache

Changes the caching implementation used in merged_branch_names
to Redis hash keys.

app/models/repository.rb

@@ -65,8 +65,6 @@ class Repository
     xcode_config: :xcode_project?
   }.freeze
 
-  MERGED_BRANCH_NAMES_CACHE_DURATION = 10.minutes
-
   def initialize(full_path, container, disk_path: nil, repo_type: Gitlab::GlRepository::PROJECT)
     @full_path = full_path
     @disk_path = disk_path || full_path
@@ -914,6 +912,8 @@ class Repository
     @root_ref_sha ||= commit(root_ref).sha
   end
 
+  # If this method is not provided a set of branch names to check merge status,
+  # it fetches all branches.
   def merged_branch_names(branch_names = [])
     # Currently we should skip caching if requesting all branch names
     # This is only used in a few places, notably app/services/branches/delete_merged_service.rb,
@@ -922,30 +922,18 @@ class Repository
     skip_cache = branch_names.empty? || Feature.disabled?(:merged_branch_names_redis_caching)
     return raw_repository.merged_branch_names(branch_names) if skip_cache
 
-    cached_branch_names = cache.read(:merged_branch_names)
-    merged_branch_names_hash = cached_branch_names || {}
-    missing_branch_names = branch_names.select { |bn| !merged_branch_names_hash.key?(bn) }
-
-    # Track some metrics here whilst feature flag is enabled
-    if cached_branch_names.present?
-      counter = Gitlab::Metrics.counter(
-        :gitlab_repository_merged_branch_names_cache_hit,
-        "Count of cache hits for Repository#merged_branch_names"
-      )
-      counter.increment(full_hit: missing_branch_names.empty?)
-    end
+    cache = redis_hash_cache
 
-    if missing_branch_names.any?
+    merged_branch_names_hash = cache.fetch_and_add_missing(:merged_branch_names, branch_names) do |missing_branch_names, hash|
       merged = raw_repository.merged_branch_names(missing_branch_names)
 
       missing_branch_names.each do |bn|
-        merged_branch_names_hash[bn] = merged.include?(bn)
+        # Redis only stores strings in hset keys, use a fancy encoder
+        hash[bn] = Gitlab::Redis::Boolean.new(merged.include?(bn))
       end
-
-      cache.write(:merged_branch_names, merged_branch_names_hash, expires_in: MERGED_BRANCH_NAMES_CACHE_DURATION)
     end
 
-    Set.new(merged_branch_names_hash.select { |_, v| v }.keys)
+    Set.new(merged_branch_names_hash.select { |_, v| Gitlab::Redis::Boolean.true?(v) }.keys)
   end
 
   def merge_base(*commits_or_ids)
@@ -1168,6 +1156,10 @@ class Repository
     @redis_set_cache ||= Gitlab::RepositorySetCache.new(self)
   end
 
+  def redis_hash_cache
+    @redis_hash_cache ||= Gitlab::RepositoryHashCache.new(self)
+  end
+
   def request_store_cache
     @request_store_cache ||= Gitlab::RepositoryCache.new(self, backend: Gitlab::SafeRequestStore)
   end

changelogs/unreleased/merged-branch-names-cache-v2.yml

+---
+title: Improvement to merged_branch_names cache
+merge_request: 24504
+author:
+type: performance

lib/gitlab/redis/boolean.rb

+# frozen_string_literal: true
+
+# A serializer for boolean values being stored in Redis.
+#
+# This is to ensure that booleans are stored in a consistent and
+# testable way when being stored as strings in Redis.
+#
+# Examples:
+#
+#     bool = Gitlab::Redis::Boolean.new(true)
+#     bool.to_s == "_b:1"
+#
+#     Gitlab::Redis::Boolean.encode(true)
+#     => "_b:1"
+#
+#     Gitlab::Redis::Boolean.decode("_b:1")
+#     => true
+#
+#     Gitlab::Redis::Boolean.true?("_b:1")
+#     => true
+#
+#     Gitlab::Redis::Boolean.true?("_b:0")
+#     => false
+
+module Gitlab
+  module Redis
+    class Boolean
+      LABEL = "_b"
+      DELIMITER = ":"
+      TRUE_STR = "1"
+      FALSE_STR = "0"
+
+      BooleanError = Class.new(StandardError)
+      NotABooleanError = Class.new(BooleanError)
+      NotAnEncodedBooleanStringError = Class.new(BooleanError)
+
+      def initialize(value)
+        @value = value
+      end
+
+      # @return [String] the encoded boolean
+      def to_s
+        self.class.encode(@value)
+      end
+
+      class << self
+        # Turn a boolean into a string for storage in Redis
+        #
+        # @param value [Boolean] true or false
+        # @return [String] the encoded boolean
+        # @raise [NotABooleanError] if the value isn't true or false
+        def encode(value)
+          raise NotABooleanError.new(value) unless bool?(value)
+
+          [LABEL, to_string(value)].join(DELIMITER)
+        end
+
+        # Decode a boolean string
+        #
+        # @param value [String] the stored boolean string
+        # @return [Boolean] true or false
+        # @raise [NotAnEncodedBooleanStringError] if the provided value isn't an encoded boolean
+        def decode(value)
+          raise NotAnEncodedBooleanStringError.new(value.class) unless value.is_a?(String)
+
+          label, bool_str = *value.split(DELIMITER, 2)
+
+          raise NotAnEncodedBooleanStringError.new(label) unless label == LABEL
+
+          from_string(bool_str)
+        end
+
+        # Decode a boolean string, then test if it's true
+        #
+        # @param value [String] the stored boolean string
+        # @return [Boolean] is the value true?
+        # @raise [NotAnEncodedBooleanStringError] if the provided value isn't an encoded boolean
+        def true?(encoded_value)
+          decode(encoded_value)
+        end
+
+        # Decode a boolean string, then test if it's false
+        #
+        # @param value [String] the stored boolean string
+        # @return [Boolean] is the value false?
+        # @raise [NotAnEncodedBooleanStringError] if the provided value isn't an encoded boolean
+        def false?(encoded_value)
+          !true?(encoded_value)
+        end
+
+        private
+
+        def bool?(value)
+          [true, false].include?(value)
+        end
+
+        def to_string(bool)
+          bool ? TRUE_STR : FALSE_STR
+        end
+
+        def from_string(str)
+          raise NotAnEncodedBooleanStringError.new(str) unless [TRUE_STR, FALSE_STR].include?(str)
+
+          str == TRUE_STR
+        end
+      end
+    end
+  end
+end

lib/gitlab/repository_cache_adapter.rb

@@ -132,6 +132,11 @@ module Gitlab
       raise NotImplementedError
     end
 
+    # RepositoryHashCache to be used. Should be overridden by the including class
+    def redis_hash_cache
+      raise NotImplementedError
+    end
+
     # List of cached methods. Should be overridden by the including class
     def cached_methods
       raise NotImplementedError
@@ -215,6 +220,7 @@ module Gitlab
       end
 
       expire_redis_set_method_caches(methods)
+      expire_redis_hash_method_caches(methods)
       expire_request_store_method_caches(methods)
     end
 
@@ -234,6 +240,10 @@ module Gitlab
       methods.each { |name| redis_set_cache.expire(name) }
     end
 
+    def expire_redis_hash_method_caches(methods)
+      methods.each { |name| redis_hash_cache.delete(name) }
+    end
+
     # All cached repository methods depend on the existence of a Git repository,
     # so if the repository doesn't exist, we already know not to call it.
     def fallback_early?(method_name)

lib/gitlab/repository_hash_cache.rb

+# frozen_string_literal: true
+
+# Interface to the Redis-backed cache store for keys that use a Redis HSET.
+# This is currently used as an incremental cache by the `Repository` model
+# for `#merged_branch_names`. It works slightly differently to the other
+# repository cache classes in that it is intended to work with partial
+# caches which can be updated with new data, using the Redis hash system.
+
+module Gitlab
+  class RepositoryHashCache
+    attr_reader :repository, :namespace, :expires_in
+
+    RepositoryHashCacheError = Class.new(StandardError)
+    InvalidKeysProvidedError = Class.new(RepositoryHashCacheError)
+    InvalidHashProvidedError = Class.new(RepositoryHashCacheError)
+
+    # @param repository [Repository]
+    # @param extra_namespace [String]
+    # @param expires_in [Integer] expiry time for hash store keys
+    def initialize(repository, extra_namespace: nil, expires_in: 1.day)
+      @repository = repository
+      @namespace = "#{repository.full_path}"
+      @namespace += ":#{repository.project.id}" if repository.project
+      @namespace = "#{@namespace}:#{extra_namespace}" if extra_namespace
+      @expires_in = expires_in
+    end
+
+    # @param type [String]
+    # @return [String]
+    def cache_key(type)
+      "#{type}:#{namespace}:hash"
+    end
+
+    # @param key [String]
+    # @return [Integer] 0 or 1 depending on success
+    def delete(key)
+      with { |redis| redis.del(cache_key(key)) }
+    end
+
+    # Check if the provided hash key exists in the hash.
+    #
+    # @param key [String]
+    # @param h_key [String] the key to check presence in Redis
+    # @return [True, False]
+    def key?(key, h_key)
+      with { |redis| redis.hexists(cache_key(key), h_key) }
+    end
+
+    # Read the values of a set of keys from the hash store, and return them
+    # as a hash of those keys and their values.
+    #
+    # @param key [String]
+    # @param hash_keys [Array<String>] an array of keys to retrieve from the store
+    # @return [Hash] a Ruby hash of the provided keys and their values from the store
+    def read_members(key, hash_keys = [])
+      raise InvalidKeysProvidedError unless hash_keys.is_a?(Array) && hash_keys.any?
+
+      with do |redis|
+        # Fetch an array of values for the supplied keys
+        values = redis.hmget(cache_key(key), hash_keys)
+
+        # Turn it back into a hash
+        hash_keys.zip(values).to_h
+      end
+    end
+
+    # Write a hash to the store. All keys and values will be strings when stored.
+    #
+    # @param key [String]
+    # @param hash [Hash] the hash to be written to Redis
+    # @return [Boolean] whether all operations were successful or not
+    def write(key, hash)
+      raise InvalidHashProvidedError unless hash.is_a?(Hash) && hash.any?
+
+      full_key = cache_key(key)
+
+      with do |redis|
+        results = redis.pipelined do
+          # Set each hash key to the provided value
+          hash.each do |h_key, h_value|
+            redis.hset(full_key, h_key, h_value)
+          end
+
+          # Update the expiry time for this hset
+          redis.expire(full_key, expires_in)
+        end
+
+        results.all?
+      end
+    end
+
+    # A variation on the `fetch` pattern of other cache stores. This method
+    # allows you to attempt to fetch a group of keys from the hash store, and
+    # for any keys that are missing values a block is then called to provide
+    # those values, which are then written back into Redis. Both sets of data
+    # are then combined and returned as one hash.
+    #
+    # @param key [String]
+    # @param h_keys [Array<String>] the keys to fetch or add to the cache
+    # @yieldparam missing_keys [Array<String>] the keys missing from the cache
+    # @yieldparam new_values [Hash] the hash to be populated by the block
+    # @return [Hash] the amalgamated hash of cached and uncached values
+    def fetch_and_add_missing(key, h_keys, &block)
+      # Check the cache for all supplied keys
+      cache_values = read_members(key, h_keys)
+
+      # Find the results which returned nil (meaning they're not in the cache)
+      missing = cache_values.select { |_, v| v.nil? }.keys
+
+      if missing.any?
+        new_values = {}
+
+        # Run the block, which updates the new_values hash
+        yield(missing, new_values)
+
+        # Ensure all values are converted to strings, to ensure merging hashes
+        # below returns standardised data.
+        new_values = standardize_hash(new_values)
+
+        # Write the new values to the hset
+        write(key, new_values)
+
+        # Merge the two sets of values to return a complete hash
+        cache_values.merge!(new_values)
+      end
+
+      record_metrics(key, cache_values, missing)
+
+      cache_values
+    end
+
+    private
+
+    def with(&blk)
+      Gitlab::Redis::Cache.with(&blk) # rubocop:disable CodeReuse/ActiveRecord
+    end
+
+    # Take a hash and convert both keys and values to strings, for insertion into Redis.
+    #
+    # @param hash [Hash]
+    # @return [Hash] the stringified hash
+    def standardize_hash(hash)
+      hash.map { |k, v| [k.to_s, v.to_s] }.to_h
+    end
+
+    # Record metrics in Prometheus.
+    #
+    # @param key [String] the basic key, e.g. :merged_branch_names. Not record-specific.
+    # @param cache_values [Hash] the hash response from the cache read
+    # @param missing_keys [Array<String>] the array of missing keys from the cache read
+    def record_metrics(key, cache_values, missing_keys)
+      cache_hits = cache_values.delete_if { |_, v| v.nil? }
+
+      # Increment the counter if we have hits
+      metrics_hit_counter.increment(full_hit: missing_keys.empty?, store_type: key) if cache_hits.any?
+
+      # Track the number of hits we got
+      metrics_hit_histogram.observe({ type: "hits", store_type: key }, cache_hits.size)
+      metrics_hit_histogram.observe({ type: "misses", store_type: key }, missing_keys.size)
+    end
+
+    def metrics_hit_counter
+      @counter ||= Gitlab::Metrics.counter(
+        :gitlab_repository_hash_cache_hit,
+        "Count of cache hits in Redis HSET"
+      )
+    end
+
+    def metrics_hit_histogram
+      @histogram ||= Gitlab::Metrics.histogram(
+        :gitlab_repository_hash_cache_size,
+        "Number of records in the HSET"
+      )
+    end
+  end
+end

spec/lib/gitlab/redis/boolean_spec.rb

+# frozen_string_literal: true
+
+require "spec_helper"
+
+describe Gitlab::Redis::Boolean do
+  subject(:redis_boolean) { described_class.new(bool) }
+
+  let(:bool) { true }
+  let(:label_section) { "#{described_class::LABEL}#{described_class::DELIMITER}" }
+
+  describe "#to_s" do
+    subject { redis_boolean.to_s }
+
+    context "true" do
+      let(:bool) { true }
+
+      it { is_expected.to eq("#{label_section}#{described_class::TRUE_STR}") }
+    end
+
+    context "false" do
+      let(:bool) { false }
+
+      it { is_expected.to eq("#{label_section}#{described_class::FALSE_STR}") }
+    end
+  end
+
+  describe ".encode" do
+    subject { redis_boolean.class.encode(bool) }
+
+    context "true" do
+      let(:bool) { true }
+
+      it { is_expected.to eq("#{label_section}#{described_class::TRUE_STR}") }
+    end
+
+    context "false" do
+      let(:bool) { false }
+
+      it { is_expected.to eq("#{label_section}#{described_class::FALSE_STR}") }
+    end
+  end
+
+  describe ".decode" do
+    subject { redis_boolean.class.decode(str) }
+
+    context "valid encoded bool" do
+      let(:str) { "#{label_section}#{bool_str}" }
+
+      context "true" do
+        let(:bool_str) { described_class::TRUE_STR }
+
+        it { is_expected.to be(true) }
+      end
+
+      context "false" do
+        let(:bool_str) { described_class::FALSE_STR }
+
+        it { is_expected.to be(false) }
+      end
+    end
+
+    context "partially invalid bool" do
+      let(:str) { "#{label_section}whoops" }
+
+      it "raises an error" do
+        expect { subject }.to raise_error(described_class::NotAnEncodedBooleanStringError)
+      end
+    end
+
+    context "invalid encoded bool" do
+      let(:str) { "whoops" }
+
+      it "raises an error" do
+        expect { subject }.to raise_error(described_class::NotAnEncodedBooleanStringError)
+      end
+    end
+  end
+
+  describe ".true?" do
+    subject { redis_boolean.class.true?(str) }
+
+    context "valid encoded bool" do
+      let(:str) { "#{label_section}#{bool_str}" }
+
+      context "true" do
+        let(:bool_str) { described_class::TRUE_STR }
+
+        it { is_expected.to be(true) }
+      end
+
+      context "false" do
+        let(:bool_str) { described_class::FALSE_STR }
+
+        it { is_expected.to be(false) }
+      end
+    end
+
+    context "partially invalid bool" do
+      let(:str) { "#{label_section}whoops" }
+
+      it "raises an error" do
+        expect { subject }.to raise_error(described_class::NotAnEncodedBooleanStringError)
+      end
+    end
+
+    context "invalid encoded bool" do
+      let(:str) { "whoops" }
+
+      it "raises an error" do
+        expect { subject }.to raise_error(described_class::NotAnEncodedBooleanStringError)
+      end
+    end
+  end
+
+  describe ".false?" do
+    subject { redis_boolean.class.false?(str) }
+
+    context "valid encoded bool" do
+      let(:str) { "#{label_section}#{bool_str}" }
+
+      context "true" do
+        let(:bool_str) { described_class::TRUE_STR }
+
+        it { is_expected.to be(false) }
+      end
+
+      context "false" do
+        let(:bool_str) { described_class::FALSE_STR }
+
+        it { is_expected.to be(true) }
+      end
+    end
+
+    context "partially invalid bool" do
+      let(:str) { "#{label_section}whoops" }
+
+      it "raises an error" do
+        expect { subject }.to raise_error(described_class::NotAnEncodedBooleanStringError)
+      end
+    end
+
+    context "invalid encoded bool" do
+      let(:str) { "whoops" }
+
+      it "raises an error" do
+        expect { subject }.to raise_error(described_class::NotAnEncodedBooleanStringError)
+      end
+    end
+  end
+end

spec/lib/gitlab/repository_cache_adapter_spec.rb

@@ -7,6 +7,7 @@ describe Gitlab::RepositoryCacheAdapter do
   let(:repository) { project.repository }
   let(:cache) { repository.send(:cache) }
   let(:redis_set_cache) { repository.send(:redis_set_cache) }
+  let(:redis_hash_cache) { repository.send(:redis_hash_cache) }
 
   describe '#cache_method_output', :use_clean_rails_memory_store_caching do
     let(:fallback) { 10 }
@@ -212,6 +213,8 @@ describe Gitlab::RepositoryCacheAdapter do
       expect(cache).to receive(:expire).with(:branch_names)
       expect(redis_set_cache).to receive(:expire).with(:rendered_readme)
       expect(redis_set_cache).to receive(:expire).with(:branch_names)
+      expect(redis_hash_cache).to receive(:delete).with(:rendered_readme)
+      expect(redis_hash_cache).to receive(:delete).with(:branch_names)
 
       repository.expire_method_caches(%i(rendered_readme branch_names))
     end

spec/lib/gitlab/repository_hash_cache_spec.rb

+# frozen_string_literal: true
+
+require "spec_helper"
+
+describe Gitlab::RepositoryHashCache, :clean_gitlab_redis_cache do
+  let_it_be(:project) { create(:project) }
+  let(:repository) { project.repository }
+  let(:namespace) { "#{repository.full_path}:#{project.id}" }
+  let(:cache) { described_class.new(repository) }
+  let(:test_hash) do
+    { "test" => "value" }
+  end
+
+  describe "#cache_key" do
+    subject { cache.cache_key(:example) }
+
+    it "includes the namespace" do
+      is_expected.to eq("example:#{namespace}:hash")
+    end
+
+    context "with a given namespace" do
+      let(:extra_namespace) { "my:data" }
+      let(:cache) { described_class.new(repository, extra_namespace: extra_namespace) }
+
+      it "includes the full namespace" do
+        is_expected.to eq("example:#{namespace}:#{extra_namespace}:hash")
+      end
+    end
+  end
+
+  describe "#delete" do
+    subject { cache.delete(:example) }
+
+    context "key exists" do
+      before do
+        cache.write(:example, test_hash)
+      end
+
+      it { is_expected.to eq(1) }
+
+      it "deletes the given key from the cache" do
+        subject
+
+        expect(cache.read_members(:example, ["test"])).to eq({ "test" => nil })
+      end
+    end
+
+    context "key doesn't exist" do
+      it { is_expected.to eq(0) }
+    end
+  end
+
+  describe "#key?" do
+    subject { cache.key?(:example, "test") }
+
+    context "key exists" do
+      before do
+        cache.write(:example, test_hash)
+      end
+
+      it { is_expected.to be(true) }
+    end
+
+    context "key doesn't exist" do
+      it { is_expected.to be(false) }
+    end
+  end
+
+  describe "#read_members" do
+    subject { cache.read_members(:example, keys) }
+
+    let(:keys) { %w(test missing) }
+
+    context "all data is cached" do
+      before do
+        cache.write(:example, test_hash.merge({ "missing" => false }))
+      end
+
+      it { is_expected.to eq({ "test" => "value", "missing" => "false" }) }
+    end
+
+    context "partial data is cached" do
+      before do
+        cache.write(:example, test_hash)
+      end
+
+      it { is_expected.to eq({ "test" => "value", "missing" => nil }) }
+    end
+
+    context "no data is cached" do
+      it { is_expected.to eq({ "test" => nil, "missing" => nil }) }
+    end
+
+    context "empty keys are passed for some reason" do
+      let(:keys) { [] }
+
+      it "raises an error" do
+        expect { subject }.to raise_error(Gitlab::RepositoryHashCache::InvalidKeysProvidedError)
+      end
+    end
+  end
+
+  describe "#write" do
+    subject { cache.write(:example, test_hash) }
+
+    it { is_expected.to be(true) }
+
+    it "actually writes stuff to Redis" do
+      subject
+
+      expect(cache.read_members(:example, ["test"])).to eq(test_hash)
+    end
+  end
+
+  describe "#fetch_and_add_missing" do
+    subject do
+      cache.fetch_and_add_missing(:example, keys) do |missing_keys, hash|
+        missing_keys.each do |key|
+          hash[key] = "was_missing"
+        end
+      end
+    end
+
+    let(:keys) { %w(test) }
+
+    it "records metrics" do
+      # Here we expect it to receive "test" as a missing key because we
+      # don't write to the cache before this test
+      expect(cache).to receive(:record_metrics).with(:example, { "test" => "was_missing" }, ["test"])
+
+      subject
+    end
+
+    context "fully cached" do
+      let(:keys) { %w(test another) }
+
+      before do
+        cache.write(:example, test_hash.merge({ "another" => "not_missing" }))
+      end
+
+      it "returns a hash" do
+        is_expected.to eq({ "test" => "value", "another" => "not_missing" })
+      end
+
+      it "doesn't write to the cache" do
+        expect(cache).not_to receive(:write)
+
+        subject
+      end
+    end
+
+    context "partially cached" do
+      let(:keys) { %w(test missing) }
+
+      before do
+        cache.write(:example, test_hash)
+      end
+
+      it "returns a hash" do
+        is_expected.to eq({ "test" => "value", "missing" => "was_missing" })
+      end
+
+      it "writes to the cache" do
+        expect(cache).to receive(:write).with(:example, { "missing" => "was_missing" })
+
+        subject
+      end
+    end
+
+    context "uncached" do
+      let(:keys) { %w(test missing) }
+
+      it "returns a hash" do
+        is_expected.to eq({ "test" => "was_missing", "missing" => "was_missing" })
+      end
+
+      it "writes to the cache" do
+        expect(cache).to receive(:write).with(:example, { "test" => "was_missing", "missing" => "was_missing" })
+
+        subject
+      end
+    end
+  end
+end

spec/models/repository_spec.rb

@@ -500,45 +500,62 @@ describe Repository do
     let(:branch_names) { %w(test beep boop definitely_merged) }
     let(:already_merged) { Set.new(["definitely_merged"]) }
 
-    let(:merge_state_hash) do
+    let(:write_hash) do
       {
-        "test" => false,
-        "beep" => false,
-        "boop" => false,
-        "definitely_merged" => true
+        "test" => Gitlab::Redis::Boolean.new(false).to_s,
+        "beep" => Gitlab::Redis::Boolean.new(false).to_s,
+        "boop" => Gitlab::Redis::Boolean.new(false).to_s,
+        "definitely_merged" => Gitlab::Redis::Boolean.new(true).to_s
       }
     end
 
-    let_it_be(:cache) do
-      caching_config_hash = Gitlab::Redis::Cache.params
-      ActiveSupport::Cache.lookup_store(:redis_cache_store, caching_config_hash)
-    end
-
-    let(:repository_cache) do
-      Gitlab::RepositoryCache.new(repository, backend: Rails.cache)
+    let(:read_hash) do
+      {
+        "test" => Gitlab::Redis::Boolean.new(false).to_s,
+        "beep" => Gitlab::Redis::Boolean.new(false).to_s,
+        "boop" => Gitlab::Redis::Boolean.new(false).to_s,
+        "definitely_merged" => Gitlab::Redis::Boolean.new(true).to_s
+      }
     end
 
-    let(:cache_key) { repository_cache.cache_key(:merged_branch_names) }
+    let(:cache) { repository.send(:redis_hash_cache) }
+    let(:cache_key) { cache.cache_key(:merged_branch_names) }
 
     before do
-      allow(Rails).to receive(:cache) { cache }
-      allow(repository).to receive(:cache) { repository_cache }
       allow(repository.raw_repository).to receive(:merged_branch_names).with(branch_names).and_return(already_merged)
     end
 
     it { is_expected.to eq(already_merged) }
     it { is_expected.to be_a(Set) }
 
+    describe "cache expiry" do
+      before do
+        allow(cache).to receive(:delete).with(anything)
+      end
+
+      it "is expired when the branches caches are expired" do
+        expect(cache).to receive(:delete).with(:merged_branch_names).at_least(:once)
+
+        repository.send(:expire_branches_cache)
+      end
+
+      it "is expired when the repository caches are expired" do
+        expect(cache).to receive(:delete).with(:merged_branch_names).at_least(:once)
+
+        repository.send(:expire_all_method_caches)
+      end
+    end
+
     context "cache is empty" do
       before do
-        cache.delete(cache_key)
+        cache.delete(:merged_branch_names)
       end
 
       it { is_expected.to eq(already_merged) }
 
       describe "cache values" do
         it "writes the values to redis" do
-          expect(cache).to receive(:write).with(cache_key, merge_state_hash, expires_in: Repository::MERGED_BRANCH_NAMES_CACHE_DURATION)
+          expect(cache).to receive(:write).with(:merged_branch_names, write_hash)
 
           subject
         end
@@ -546,14 +563,14 @@ describe Repository do
         it "matches the supplied hash" do
           subject
 
-          expect(cache.read(cache_key)).to eq(merge_state_hash)
+          expect(cache.read_members(:merged_branch_names, branch_names)).to eq(read_hash)
         end
       end
     end
 
     context "cache is not empty" do
       before do
-        cache.write(cache_key, merge_state_hash)
+        cache.write(:merged_branch_names, write_hash)
       end
 
       it { is_expected.to eq(already_merged) }
@@ -568,8 +585,8 @@ describe Repository do
     context "cache is partially complete" do
       before do
         allow(repository.raw_repository).to receive(:merged_branch_names).with(["boop"]).and_return([])
-        hash = merge_state_hash.except("boop")
-        cache.write(cache_key, hash)
+        hash = write_hash.except("boop")
+        cache.write(:merged_branch_names, hash)
       end
 
       it { is_expected.to eq(already_merged) }