Cache branch and tag names as Redis sets

This allows us to check inclusion for the *_exists? methods without
downloading the full list of branch names, which is over 100KiB in size
for gitlab-ce at the moment.

1 files changed, 67 insertions, 0 deletions

diff --git a/lib/gitlab/repository_set_cache.rb b/lib/gitlab/repository_set_cache.rb
new file mode 100644
index 00000000000..fb634328a95
--- /dev/null
+++ b/lib/gitlab/repository_set_cache.rb
@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+# Interface to the Redis-backed cache store for keys that use a Redis set
+module Gitlab
+  class RepositorySetCache
+    attr_reader :repository, :namespace, :expires_in
+
+    def initialize(repository, extra_namespace: nil, expires_in: 2.weeks)
+      @repository = repository
+      @namespace = "#{repository.full_path}:#{repository.project.id}"
+      @namespace = "#{@namespace}:#{extra_namespace}" if extra_namespace
+      @expires_in = expires_in
+    end
+
+    def cache_key(type)
+      [type, namespace, 'set'].join(':')
+    end
+
+    def expire(key)
+      with { |redis| redis.del(cache_key(key)) }
+    end
+
+    def exist?(key)
+      with { |redis| redis.exists(cache_key(key)) }
+    end
+
+    def read(key)
+      with { |redis| redis.smembers(cache_key(key)) }
+    end
+
+    def write(key, value)
+      full_key = cache_key(key)
+
+      with do |redis|
+        redis.multi do
+          redis.del(full_key)
+
+          # Splitting into groups of 1000 prevents us from creating a too-long
+          # Redis command
+          value.in_groups_of(1000, false) { |subset| redis.sadd(full_key, subset) }
+
+          redis.expire(full_key, expires_in)
+        end
+      end
+
+      value
+    end
+
+    def fetch(key, &block)
+      if exist?(key)
+        read(key)
+      else
+        write(key, yield)
+      end
+    end
+
+    def include?(key, value)
+      with { |redis| redis.sismember(cache_key(key), value) }
+    end
+
+    private
+
+    def with(&blk)
+      Gitlab::Redis::Cache.with(&blk) # rubocop:disable CodeReuse/ActiveRecord
+    end
+  end
+end