Add markdown cache columns to the database, but don't use them yet

This commit adds a number of _html columns and, with the exception of Note,
starts updating them whenever the content of their partner fields changes.

Note has a collision with the note_html attr_accessor; that will be fixed later

A background worker for clearing these cache columns is also introduced - use
`rake cache:clear` to set it off. You can clear the database or Redis caches
separately by running `rake cache:clear:db` or `rake cache:clear:redis`,
respectively.

34 files changed, 689 insertions, 49 deletions

diff --git a/app/helpers/gitlab_markdown_helper.rb b/app/helpers/gitlab_markdown_helper.rb
index 1a259656f31..d24680b8617 100644
--- a/app/helpers/gitlab_markdown_helper.rb
+++ b/app/helpers/gitlab_markdown_helper.rb
@@ -51,17 +51,15 @@ module GitlabMarkdownHelper
     context[:project] ||= @project
 
     html = Banzai.render(text, context)
+    banzai_postprocess(html, context)
+  end
 
-    context.merge!(
-      current_user:   (current_user if defined?(current_user)),
+  def markdown_field(object, field)
+    object = object.for_display if object.respond_to?(:for_display)
+    return "" unless object.present?
 
-      # RelativeLinkFilter
-      requested_path: @path,
-      project_wiki:   @project_wiki,
-      ref:            @ref
-    )
-
-    Banzai.post_process(html, context)
+    html = Banzai.render_field(object, field)
+    banzai_postprocess(html, object.banzai_render_context(field))
   end
 
   def asciidoc(text)
@@ -196,4 +194,18 @@ module GitlabMarkdownHelper
       icon(options[:icon])
     end
   end
+
+  # Calls Banzai.post_process with some common context options
+  def banzai_postprocess(html, context)
+    context.merge!(
+      current_user:   (current_user if defined?(current_user)),
+
+      # RelativeLinkFilter
+      requested_path: @path,
+      project_wiki:   @project_wiki,
+      ref:            @ref
+    )
+
+    Banzai.post_process(html, context)
+  end
 end
diff --git a/app/models/abuse_report.rb b/app/models/abuse_report.rb
index b01a244032d..2340453831e 100644
--- a/app/models/abuse_report.rb
+++ b/app/models/abuse_report.rb
@@ -1,4 +1,8 @@
 class AbuseReport < ActiveRecord::Base
+  include CacheMarkdownField
+
+  cache_markdown_field :message, pipeline: :single_line
+
   belongs_to :reporter, class_name: 'User'
   belongs_to :user
 
@@ -7,6 +11,9 @@ class AbuseReport < ActiveRecord::Base
   validates :message, presence: true
   validates :user_id, uniqueness: { message: 'has already been reported' }
 
+  # For CacheMarkdownField
+  alias_method :author, :reporter
+
   def remove_user(deleted_by:)
     user.block
     DeleteUserWorker.perform_async(deleted_by.id, user.id, delete_solo_owned_groups: true)
diff --git a/app/models/appearance.rb b/app/models/appearance.rb
index 4cf8dd9a8ce..e4106e1c2e9 100644
--- a/app/models/appearance.rb
+++ b/app/models/appearance.rb
@@ -1,4 +1,8 @@
 class Appearance < ActiveRecord::Base
+  include CacheMarkdownField
+
+  cache_markdown_field :description
+
   validates :title,       presence: true
   validates :description, presence: true
   validates :logo,        file_size: { maximum: 1.megabyte }
diff --git a/app/models/application_setting.rb b/app/models/application_setting.rb
index 55d2e07de08..c99aa7772bb 100644
--- a/app/models/application_setting.rb
+++ b/app/models/application_setting.rb
@@ -1,5 +1,7 @@
 class ApplicationSetting < ActiveRecord::Base
+  include CacheMarkdownField
   include TokenAuthenticatable
+
   add_authentication_token_field :runners_registration_token
   add_authentication_token_field :health_check_access_token
 
@@ -17,6 +19,11 @@ class ApplicationSetting < ActiveRecord::Base
   serialize :domain_whitelist, Array
   serialize :domain_blacklist, Array
 
+  cache_markdown_field :sign_in_text
+  cache_markdown_field :help_page_text
+  cache_markdown_field :shared_runners_text, pipeline: :plain_markdown
+  cache_markdown_field :after_sign_up_text
+
   attr_accessor :domain_whitelist_raw, :domain_blacklist_raw
 
   validates :session_expire_delay,
diff --git a/app/models/broadcast_message.rb b/app/models/broadcast_message.rb
index 61498140f27..cb40f33932a 100644
--- a/app/models/broadcast_message.rb
+++ b/app/models/broadcast_message.rb
@@ -1,6 +1,9 @@
 class BroadcastMessage < ActiveRecord::Base
+  include CacheMarkdownField
   include Sortable
 
+  cache_markdown_field :message, pipeline: :broadcast_message
+
   validates :message,   presence: true
   validates :starts_at, presence: true
   validates :ends_at,   presence: true
diff --git a/app/models/concerns/cache_markdown_field.rb b/app/models/concerns/cache_markdown_field.rb
new file mode 100644
index 00000000000..90bd6490a02
--- /dev/null
+++ b/app/models/concerns/cache_markdown_field.rb
@@ -0,0 +1,131 @@
+# This module takes care of updating cache columns for Markdown-containing
+# fields. Use like this in the body of your class:
+#
+#     include CacheMarkdownField
+#     cache_markdown_field :foo
+#     cache_markdown_field :bar
+#     cache_markdown_field :baz, pipeline: :single_line
+#
+# Corresponding foo_html, bar_html and baz_html fields should exist.
+module CacheMarkdownField
+  # Knows about the relationship between markdown and html field names, and
+  # stores the rendering contexts for the latter
+  class FieldData
+    extend Forwardable
+
+    def initialize
+      @data = {}
+    end
+
+    def_delegators :@data, :[], :[]=
+    def_delegator :@data, :keys, :markdown_fields
+
+    def html_field(markdown_field)
+      "#{markdown_field}_html"
+    end
+
+    def html_fields
+      markdown_fields.map {|field| html_field(field) }
+    end
+  end
+
+  # Dynamic registries don't really work in Rails as it's not guaranteed that
+  # every class will be loaded, so hardcode the list.
+  CACHING_CLASSES = %w[
+    AbuseReport
+    Appearance
+    ApplicationSetting
+    BroadcastMessage
+    Issue
+    Label
+    MergeRequest
+    Milestone
+    Namespace
+    Note
+    Project
+    Release
+    Snippet
+  ]
+
+  def self.caching_classes
+    CACHING_CLASSES.map(&:constantize)
+  end
+
+  extend ActiveSupport::Concern
+
+  included do
+    cattr_reader :cached_markdown_fields do
+      FieldData.new
+    end
+
+    # Returns the default Banzai render context for the cached markdown field.
+    def banzai_render_context(field)
+      raise ArgumentError.new("Unknown field: #{field.inspect}") unless
+        cached_markdown_fields.markdown_fields.include?(field)
+
+      # Always include a project key, or Banzai complains
+      project = self.project if self.respond_to?(:project)
+      context = cached_markdown_fields[field].merge(project: project)
+
+      # Banzai is less strict about authors, so don't always have an author key
+      context[:author] = self.author if self.respond_to?(:author)
+
+      context
+    end
+
+    # Allow callers to look up the cache field name, rather than hardcoding it
+    def markdown_cache_field_for(field)
+      raise ArgumentError.new("Unknown field: #{field}") unless
+        cached_markdown_fields.markdown_fields.include?(field)
+
+      cached_markdown_fields.html_field(field)
+    end
+
+    # Always exclude _html fields from attributes (including serialization).
+    # They contain unredacted HTML, which would be a security issue
+    alias_method :attributes_before_markdown_cache, :attributes
+    def attributes
+      attrs = attributes_before_markdown_cache
+
+      cached_markdown_fields.html_fields.each do |field|
+        attrs.delete(field)
+      end
+
+      attrs
+    end
+  end
+
+  class_methods do
+    private
+
+    # Specify that a field is markdown. Its rendered output will be cached in
+    # a corresponding _html field. Any custom rendering options may be provided
+    # as a context.
+    def cache_markdown_field(markdown_field, context = {})
+      raise "Add #{self} to CacheMarkdownField::CACHING_CLASSES" unless
+        CacheMarkdownField::CACHING_CLASSES.include?(self.to_s)
+
+      cached_markdown_fields[markdown_field] = context
+
+      html_field = cached_markdown_fields.html_field(markdown_field)
+      cache_method = "#{markdown_field}_cache_refresh".to_sym
+      invalidation_method = "#{html_field}_invalidated?".to_sym
+
+      define_method(cache_method) do
+        html = Banzai::Renderer.cacheless_render_field(self, markdown_field)
+        __send__("#{html_field}=", html)
+        true
+      end
+
+      # The HTML becomes invalid if any dependent fields change. For now, assume
+      # author and project invalidate the cache in all circumstances.
+      define_method(invalidation_method) do
+        changed_fields = changed_attributes.keys
+        invalidations = changed_fields & [markdown_field.to_s, "author", "project"]
+        !invalidations.empty?
+      end
+
+      before_save cache_method, if: invalidation_method
+    end
+  end
+end
diff --git a/app/models/concerns/issuable.rb b/app/models/concerns/issuable.rb
index ff465d2c745..c4b42ad82c7 100644
--- a/app/models/concerns/issuable.rb
+++ b/app/models/concerns/issuable.rb
@@ -6,6 +6,7 @@
 #
 module Issuable
   extend ActiveSupport::Concern
+  include CacheMarkdownField
   include Participable
   include Mentionable
   include Subscribable
@@ -13,6 +14,9 @@ module Issuable
   include Awardable
 
   included do
+    cache_markdown_field :title, pipeline: :single_line
+    cache_markdown_field :description
+
     belongs_to :author, class_name: "User"
     belongs_to :assignee, class_name: "User"
     belongs_to :updated_by, class_name: "User"
diff --git a/app/models/global_label.rb b/app/models/global_label.rb
index ddd4bad5c21..698a7bbd327 100644
--- a/app/models/global_label.rb
+++ b/app/models/global_label.rb
@@ -4,6 +4,10 @@ class GlobalLabel
 
   delegate :color, :description, to: :@first_label
 
+  def for_display
+    @first_label
+  end
+
   def self.build_collection(labels)
     labels = labels.group_by(&:title)
 
diff --git a/app/models/global_milestone.rb b/app/models/global_milestone.rb
index bda2b5c5d5d..cde4a568577 100644
--- a/app/models/global_milestone.rb
+++ b/app/models/global_milestone.rb
@@ -4,6 +4,10 @@ class GlobalMilestone
   attr_accessor :title, :milestones
   alias_attribute :name, :title
 
+  def for_display
+    @first_milestone
+  end
+
   def self.build_collection(milestones)
     milestones = milestones.group_by(&:title)
 
@@ -17,6 +21,7 @@ class GlobalMilestone
     @title = title
     @name = title
     @milestones = milestones
+    @first_milestone = milestones.find {|m| m.description.present? } || milestones.first
   end
 
   def safe_title
diff --git a/app/models/label.rb b/app/models/label.rb
index a23140b7d64..e8e12e2904e 100644
--- a/app/models/label.rb
+++ b/app/models/label.rb
@@ -1,4 +1,5 @@
 class Label < ActiveRecord::Base
+  include CacheMarkdownField
   include Referable
   include Subscribable
 
@@ -8,6 +9,8 @@ class Label < ActiveRecord::Base
   None = LabelStruct.new('No Label', 'No Label')
   Any = LabelStruct.new('Any Label', '')
 
+  cache_markdown_field :description, pipeline: :single_line
+
   DEFAULT_COLOR = '#428BCA'
 
   default_value_for :color, DEFAULT_COLOR
diff --git a/app/models/milestone.rb b/app/models/milestone.rb
index 44c3cbb2c73..23aecbfa3a6 100644
--- a/app/models/milestone.rb
+++ b/app/models/milestone.rb
@@ -6,12 +6,16 @@ class Milestone < ActiveRecord::Base
   Any = MilestoneStruct.new('Any Milestone', '', -1)
   Upcoming = MilestoneStruct.new('Upcoming', '#upcoming', -2)
 
+  include CacheMarkdownField
   include InternalId
   include Sortable
   include Referable
   include StripAttribute
   include Milestoneish
 
+  cache_markdown_field :title, pipeline: :single_line
+  cache_markdown_field :description
+
   belongs_to :project
   has_many :issues
   has_many :labels, -> { distinct.reorder('labels.title') },  through: :issues
diff --git a/app/models/namespace.rb b/app/models/namespace.rb
index 919b3b1f095..b7f2b2bbe61 100644
--- a/app/models/namespace.rb
+++ b/app/models/namespace.rb
@@ -1,9 +1,12 @@
 class Namespace < ActiveRecord::Base
   acts_as_paranoid
 
+  include CacheMarkdownField
   include Sortable
   include Gitlab::ShellAdapter
 
+  cache_markdown_field :description, pipeline: :description
+
   has_many :projects, dependent: :destroy
   belongs_to :owner, class_name: "User"
 
diff --git a/app/models/project.rb b/app/models/project.rb
index ecd742a17d5..88e4bd14860 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -6,6 +6,7 @@ class Project < ActiveRecord::Base
   include Gitlab::VisibilityLevel
   include Gitlab::CurrentSettings
   include AccessRequestable
+  include CacheMarkdownField
   include Referable
   include Sortable
   include AfterCommitQueue
@@ -17,6 +18,8 @@ class Project < ActiveRecord::Base
 
   UNKNOWN_IMPORT_URL = 'http://unknown.git'
 
+  cache_markdown_field :description, pipeline: :description
+
   delegate :feature_available?, :builds_enabled?, :wiki_enabled?, :merge_requests_enabled?, to: :project_feature, allow_nil: true
 
   default_value_for :archived, false
diff --git a/app/models/release.rb b/app/models/release.rb
index e196b84eb18..c936899799e 100644
--- a/app/models/release.rb
+++ b/app/models/release.rb
@@ -1,4 +1,8 @@
 class Release < ActiveRecord::Base
+  include CacheMarkdownField
+
+  cache_markdown_field :description
+
   belongs_to :project
 
   validates :description, :project, :tag, presence: true
diff --git a/app/models/snippet.rb b/app/models/snippet.rb
index 8a1730f3f36..2373b445009 100644
--- a/app/models/snippet.rb
+++ b/app/models/snippet.rb
@@ -1,11 +1,21 @@
 class Snippet < ActiveRecord::Base
   include Gitlab::VisibilityLevel
   include Linguist::BlobHelper
+  include CacheMarkdownField
   include Participable
   include Referable
   include Sortable
   include Awardable
 
+  cache_markdown_field :title, pipeline: :single_line
+  cache_markdown_field :content
+
+  # If file_name changes, it invalidates content
+  alias_method :default_content_html_invalidator, :content_html_invalidated?
+  def content_html_invalidated?
+    default_content_html_invalidator || file_name_changed?
+  end
+
   default_value_for :visibility_level, Snippet::PRIVATE
 
   belongs_to :author, class_name: 'User'
diff --git a/app/workers/clear_database_cache_worker.rb b/app/workers/clear_database_cache_worker.rb
new file mode 100644
index 00000000000..c541daba50e
--- /dev/null
+++ b/app/workers/clear_database_cache_worker.rb
@@ -0,0 +1,23 @@
+# This worker clears all cache fields in the database, working in batches.
+class ClearDatabaseCacheWorker
+  include Sidekiq::Worker
+
+  BATCH_SIZE = 1000
+
+  def perform
+    CacheMarkdownField.caching_classes.each do |kls|
+      fields = kls.cached_markdown_fields.html_fields
+      clear_cache_fields = fields.each_with_object({}) do |field, memo|
+        memo[field] = nil
+      end
+
+      Rails.logger.debug("Clearing Markdown cache for #{kls}: #{fields.inspect}")
+
+      kls.unscoped.in_batches(of: BATCH_SIZE) do |relation|
+        relation.update_all(clear_cache_fields)
+      end
+    end
+
+    nil
+  end
+end
diff --git a/config/initializers/ar5_batching.rb b/config/initializers/ar5_batching.rb
new file mode 100644
index 00000000000..35e8b3808e2
--- /dev/null
+++ b/config/initializers/ar5_batching.rb
@@ -0,0 +1,41 @@
+# Port ActiveRecord::Relation#in_batches from ActiveRecord 5.
+# https://github.com/rails/rails/blob/ac027338e4a165273607dccee49a3d38bc836794/activerecord/lib/active_record/relation/batches.rb#L184
+# TODO: this can be removed once we're using AR5.
+raise "Vendored ActiveRecord 5 code! Delete #{__FILE__}!" if ActiveRecord::VERSION::MAJOR >= 5
+
+module ActiveRecord
+  module Batches
+    # Differences from upstream: enumerator support was removed, and custom
+    # order/limit clauses are ignored without a warning.
+    def in_batches(of: 1000, start: nil, finish: nil, load: false)
+      raise "Must provide a block" unless block_given?
+
+      relation = self.reorder(batch_order).limit(of)
+      relation = relation.where(arel_table[primary_key].gteq(start)) if start
+      relation = relation.where(arel_table[primary_key].lteq(finish)) if finish
+      batch_relation = relation
+
+      loop do
+        if load
+          records = batch_relation.records
+          ids = records.map(&:id)
+          yielded_relation = self.where(primary_key => ids)
+          yielded_relation.load_records(records)
+        else
+          ids = batch_relation.pluck(primary_key)
+          yielded_relation = self.where(primary_key => ids)
+        end
+
+        break if ids.empty?
+
+        primary_key_offset = ids.last
+        raise ArgumentError.new("Primary key not included in the custom select clause") unless primary_key_offset
+
+        yield yielded_relation
+
+        break if ids.length < of
+        batch_relation = relation.where(arel_table[primary_key].gt(primary_key_offset))
+      end
+    end
+  end
+end
diff --git a/db/migrate/20160829114652_add_markdown_cache_columns.rb b/db/migrate/20160829114652_add_markdown_cache_columns.rb
new file mode 100644
index 00000000000..8753e55e058
--- /dev/null
+++ b/db/migrate/20160829114652_add_markdown_cache_columns.rb
@@ -0,0 +1,38 @@
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddMarkdownCacheColumns < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  COLUMNS = {
+    abuse_reports: [:message],
+    appearances: [:description],
+    application_settings: [
+      :sign_in_text,
+      :help_page_text,
+      :shared_runners_text,
+      :after_sign_up_text
+    ],
+    broadcast_messages: [:message],
+    issues: [:title, :description],
+    labels: [:description],
+    merge_requests: [:title, :description],
+    milestones: [:title, :description],
+    namespaces: [:description],
+    notes: [:note],
+    projects: [:description],
+    releases: [:description],
+    snippets: [:title, :content],
+  }
+
+  def change
+    COLUMNS.each do |table, columns|
+      columns.each do |column|
+        add_column table, "#{column}_html", :text
+      end
+    end
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index ad62c249b3f..56da70b3c02 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -23,6 +23,7 @@ ActiveRecord::Schema.define(version: 20160926145521) do
     t.text     "message"
     t.datetime "created_at"
     t.datetime "updated_at"
+    t.text     "message_html"
   end
 
   create_table "appearances", force: :cascade do |t|
@@ -30,8 +31,9 @@ ActiveRecord::Schema.define(version: 20160926145521) do
     t.text     "description"
     t.string   "header_logo"
     t.string   "logo"
-    t.datetime "created_at",  null: false
-    t.datetime "updated_at",  null: false
+    t.datetime "created_at",       null: false
+    t.datetime "updated_at",       null: false
+    t.text     "description_html"
   end
 
   create_table "application_settings", force: :cascade do |t|
@@ -92,6 +94,10 @@ ActiveRecord::Schema.define(version: 20160926145521) do
     t.text     "domain_blacklist"
     t.boolean  "koding_enabled"
     t.string   "koding_url"
+    t.text     "sign_in_text_html"
+    t.text     "help_page_text_html"
+    t.text     "shared_runners_text_html"
+    t.text     "after_sign_up_text_html"
   end
 
   create_table "audit_events", force: :cascade do |t|
@@ -128,13 +134,14 @@ ActiveRecord::Schema.define(version: 20160926145521) do
   add_index "boards", ["project_id"], name: "index_boards_on_project_id", using: :btree
 
   create_table "broadcast_messages", force: :cascade do |t|
-    t.text     "message",    null: false
+    t.text     "message",      null: false
     t.datetime "starts_at"
     t.datetime "ends_at"
     t.datetime "created_at"
     t.datetime "updated_at"
     t.string   "color"
     t.string   "font"
+    t.text     "message_html"
   end
 
   create_table "ci_application_settings", force: :cascade do |t|
@@ -457,18 +464,20 @@ ActiveRecord::Schema.define(version: 20160926145521) do
     t.integer  "project_id"
     t.datetime "created_at"
     t.datetime "updated_at"
-    t.integer  "position",      default: 0
+    t.integer  "position",         default: 0
     t.string   "branch_name"
     t.text     "description"
     t.integer  "milestone_id"
     t.string   "state"
     t.integer  "iid"
     t.integer  "updated_by_id"
-    t.boolean  "confidential",  default: false
+    t.boolean  "confidential",     default: false
     t.datetime "deleted_at"
     t.date     "due_date"
     t.integer  "moved_to_id"
     t.integer  "lock_version"
+    t.text     "title_html"
+    t.text     "description_html"
   end
 
   add_index "issues", ["assignee_id"], name: "index_issues_on_assignee_id", using: :btree
@@ -514,9 +523,10 @@ ActiveRecord::Schema.define(version: 20160926145521) do
     t.integer  "project_id"
     t.datetime "created_at"
     t.datetime "updated_at"
-    t.boolean  "template",    default: false
+    t.boolean  "template",         default: false
     t.string   "description"
     t.integer  "priority"
+    t.text     "description_html"
   end
 
   add_index "labels", ["priority"], name: "index_labels_on_priority", using: :btree
@@ -632,6 +642,8 @@ ActiveRecord::Schema.define(version: 20160926145521) do
     t.datetime "deleted_at"
     t.string   "in_progress_merge_commit_sha"
     t.integer  "lock_version"
+    t.text     "title_html"
+    t.text     "description_html"
   end
 
   add_index "merge_requests", ["assignee_id"], name: "index_merge_requests_on_assignee_id", using: :btree
@@ -658,14 +670,16 @@ ActiveRecord::Schema.define(version: 20160926145521) do
   add_index "merge_requests_closing_issues", ["merge_request_id"], name: "index_merge_requests_closing_issues_on_merge_request_id", using: :btree
 
   create_table "milestones", force: :cascade do |t|
-    t.string   "title",       null: false
-    t.integer  "project_id",  null: false
+    t.string   "title",            null: false
+    t.integer  "project_id",       null: false
     t.text     "description"
     t.date     "due_date"
     t.datetime "created_at"
     t.datetime "updated_at"
     t.string   "state"
     t.integer  "iid"
+    t.text     "title_html"
+    t.text     "description_html"
   end
 
   add_index "milestones", ["description"], name: "index_milestones_on_description_trigram", using: :gin, opclasses: {"description"=>"gin_trgm_ops"}
@@ -689,6 +703,7 @@ ActiveRecord::Schema.define(version: 20160926145521) do
     t.boolean  "request_access_enabled", default: true,  null: false
     t.datetime "deleted_at"
     t.boolean  "lfs_enabled"
+    t.text     "description_html"
   end
 
   add_index "namespaces", ["created_at"], name: "index_namespaces_on_created_at", using: :btree
@@ -721,6 +736,7 @@ ActiveRecord::Schema.define(version: 20160926145521) do
     t.integer  "resolved_by_id"
     t.string   "discussion_id"
     t.string   "original_discussion_id"
+    t.text     "note_html"
   end
 
   add_index "notes", ["author_id"], name: "index_notes_on_author_id", using: :btree
@@ -872,6 +888,7 @@ ActiveRecord::Schema.define(version: 20160926145521) do
     t.boolean  "request_access_enabled",             default: true,      null: false
     t.boolean  "has_external_wiki"
     t.boolean  "lfs_enabled"
+    t.text     "description_html"
   end
 
   add_index "projects", ["ci_id"], name: "index_projects_on_ci_id", using: :btree
@@ -922,6 +939,7 @@ ActiveRecord::Schema.define(version: 20160926145521) do
     t.integer  "project_id"
     t.datetime "created_at"
     t.datetime "updated_at"
+    t.text     "description_html"
   end
 
   add_index "releases", ["project_id", "tag"], name: "index_releases_on_project_id_and_tag", using: :btree
@@ -976,6 +994,8 @@ ActiveRecord::Schema.define(version: 20160926145521) do
     t.string   "file_name"
     t.string   "type"
     t.integer  "visibility_level", default: 0, null: false
+    t.text     "title_html"
+    t.text     "content_html"
   end
 
   add_index "snippets", ["author_id"], name: "index_snippets_on_author_id", using: :btree
diff --git a/lib/banzai.rb b/lib/banzai.rb
index 9ebe379f454..35ca234c1ba 100644
--- a/lib/banzai.rb
+++ b/lib/banzai.rb
@@ -3,6 +3,10 @@ module Banzai
     Renderer.render(text, context)
   end
 
+  def self.render_field(object, field)
+    Renderer.render_field(object, field)
+  end
+
   def self.cache_collection_render(texts_and_contexts)
     Renderer.cache_collection_render(texts_and_contexts)
   end
diff --git a/lib/banzai/renderer.rb b/lib/banzai/renderer.rb
index a4ae27eefd8..6924a293da8 100644
--- a/lib/banzai/renderer.rb
+++ b/lib/banzai/renderer.rb
@@ -31,6 +31,34 @@ module Banzai
       end
     end
 
+    # Convert a Markdown-containing field on an object into an HTML-safe String
+    # of HTML. This method is analogous to calling render(object.field), but it
+    # can cache the rendered HTML in the object, rather than Redis.
+    #
+    # The context to use is learned from the passed-in object by calling
+    # #banzai_render_context(field), and cannot be changed. Use #render, passing
+    # it the field text, if a custom rendering is needed. The generated context
+    # is returned along with the HTML.
+    def render_field(object, field)
+      html_field = object.markdown_cache_field_for(field)
+
+      html = object.__send__(html_field)
+      return html if html.present?
+
+      html = cacheless_render_field(object, field)
+      object.update_column(html_field, html) unless object.new_record? || object.destroyed?
+
+      html
+    end
+
+    # Same as +render_field+, but without consulting or updating the cache field
+    def cacheless_render_field(object, field)
+      text = object.__send__(field)
+      context = object.banzai_render_context(field)
+
+      cacheless_render(text, context)
+    end
+
     # Perform multiple render from an Array of Markdown String into an
     # Array of HTML-safe String of HTML.
     #
diff --git a/lib/tasks/cache.rake b/lib/tasks/cache.rake
index 2214f855200..a95a3455a4a 100644
--- a/lib/tasks/cache.rake
+++ b/lib/tasks/cache.rake
@@ -1,22 +1,33 @@
 namespace :cache do
-  CLEAR_BATCH_SIZE = 1000 # There seems to be no speedup when pushing beyond 1,000
-  REDIS_SCAN_START_STOP = '0' # Magic value, see http://redis.io/commands/scan
+  namespace :clear do
+    REDIS_CLEAR_BATCH_SIZE = 1000 # There seems to be no speedup when pushing beyond 1,000
+    REDIS_SCAN_START_STOP = '0' # Magic value, see http://redis.io/commands/scan
 
-  desc "GitLab | Clear redis cache"
-  task :clear => :environment do
-    Gitlab::Redis.with do |redis|
-      cursor = REDIS_SCAN_START_STOP
-      loop do
-        cursor, keys = redis.scan(
-          cursor,
-          match: "#{Gitlab::Redis::CACHE_NAMESPACE}*", 
-          count: CLEAR_BATCH_SIZE
-        )
-  
-        redis.del(*keys) if keys.any?
-  
-        break if cursor == REDIS_SCAN_START_STOP
+    desc "GitLab | Clear redis cache"
+    task redis: :environment do
+      Gitlab::Redis.with do |redis|
+        cursor = REDIS_SCAN_START_STOP
+        loop do
+          cursor, keys = redis.scan(
+            cursor,
+            match: "#{Gitlab::Redis::CACHE_NAMESPACE}*",
+            count: REDIS_CLEAR_BATCH_SIZE
+          )
+
+          redis.del(*keys) if keys.any?
+
+          break if cursor == REDIS_SCAN_START_STOP
+        end
       end
     end
+
+    desc "GitLab | Clear database cache (in the background)"
+    task db: :environment do
+      ClearDatabaseCacheWorker.perform_async
+    end
+
+    task all: [:db, :redis]
   end
+
+  task clear: 'cache:clear:all'
 end
diff --git a/spec/factories/projects.rb b/spec/factories/projects.rb
index 873d3fcb5af..331172445e4 100644
--- a/spec/factories/projects.rb
+++ b/spec/factories/projects.rb
@@ -9,6 +9,9 @@ FactoryGirl.define do
     namespace
     creator
 
+    # Behaves differently to nil due to cache_has_external_issue_tracker
+    has_external_issue_tracker false
+
     trait :public do
       visibility_level Gitlab::VisibilityLevel::PUBLIC
     end
@@ -92,6 +95,8 @@ FactoryGirl.define do
   end
 
   factory :redmine_project, parent: :project do
+    has_external_issue_tracker true
+
     after :create do |project|
       project.create_redmine_service(
         active: true,
@@ -105,6 +110,8 @@ FactoryGirl.define do
   end
 
   factory :jira_project, parent: :project do
+    has_external_issue_tracker true
+
     after :create do |project|
       project.create_jira_service(
         active: true,
diff --git a/spec/lib/banzai/renderer_spec.rb b/spec/lib/banzai/renderer_spec.rb
new file mode 100644
index 00000000000..aaa6b12e67e
--- /dev/null
+++ b/spec/lib/banzai/renderer_spec.rb
@@ -0,0 +1,74 @@
+require 'spec_helper'
+
+describe Banzai::Renderer do
+  def expect_render(project = :project)
+    expected_context = { project: project }
+    expect(renderer).to receive(:cacheless_render) { :html }.with(:markdown, expected_context)
+  end
+
+  def expect_cache_update
+    expect(object).to receive(:update_column).with("field_html", :html)
+  end
+
+  def fake_object(*features)
+    markdown = :markdown if features.include?(:markdown)
+    html = :html if features.include?(:html)
+
+    object = double(
+      "object",
+      banzai_render_context: { project: :project },
+      field: markdown,
+      field_html: html
+    )
+
+    allow(object).to receive(:markdown_cache_field_for).with(:field).and_return("field_html")
+    allow(object).to receive(:new_record?).and_return(features.include?(:new))
+    allow(object).to receive(:destroyed?).and_return(features.include?(:destroyed))
+
+    object
+  end
+
+  describe "#render_field" do
+    let(:renderer) { Banzai::Renderer }
+    let(:subject) { renderer.render_field(object, :field) }
+
+    context "with an empty cache" do
+      let(:object) { fake_object(:markdown) }
+      it "caches and returns the result" do
+        expect_render
+        expect_cache_update
+        expect(subject).to eq(:html)
+      end
+    end
+
+    context "with a filled cache" do
+      let(:object) { fake_object(:markdown, :html) }
+
+      it "uses the cache" do
+        expect_render.never
+        expect_cache_update.never
+        should eq(:html)
+      end
+    end
+
+    context "new object" do
+      let(:object) { fake_object(:new, :markdown) }
+
+      it "doesn't cache the result" do
+        expect_render
+        expect_cache_update.never
+        expect(subject).to eq(:html)
+      end
+    end
+
+    context "destroyed object" do
+      let(:object) { fake_object(:destroyed, :markdown) }
+
+      it "doesn't cache the result" do
+        expect_render
+        expect_cache_update.never
+        expect(subject).to eq(:html)
+      end
+    end
+  end
+end
diff --git a/spec/lib/gitlab/import_export/attribute_configuration_spec.rb b/spec/lib/gitlab/import_export/attribute_configuration_spec.rb
index 2e19d590d83..ea65a5dfed1 100644
--- a/spec/lib/gitlab/import_export/attribute_configuration_spec.rb
+++ b/spec/lib/gitlab/import_export/attribute_configuration_spec.rb
@@ -26,10 +26,11 @@ describe 'Import/Export attribute configuration', lib: true do
   it 'has no new columns' do
     relation_names.each do |relation_name|
       relation_class = relation_class_for_name(relation_name)
+      relation_attributes = relation_class.new.attributes.keys
 
       expect(safe_model_attributes[relation_class.to_s]).not_to be_nil, "Expected exported class #{relation_class} to exist in safe_model_attributes"
 
-      current_attributes = parsed_attributes(relation_name, relation_class.attribute_names)
+      current_attributes = parsed_attributes(relation_name, relation_attributes)
       safe_attributes = safe_model_attributes[relation_class.to_s]
       new_attributes = current_attributes - safe_attributes
 
diff --git a/spec/models/abuse_report_spec.rb b/spec/models/abuse_report_spec.rb
index 305f8bc88cc..c4486a32082 100644
--- a/spec/models/abuse_report_spec.rb
+++ b/spec/models/abuse_report_spec.rb
@@ -9,6 +9,10 @@ RSpec.describe AbuseReport, type: :model do
   describe 'associations' do
     it { is_expected.to belong_to(:reporter).class_name('User') }
     it { is_expected.to belong_to(:user) }
+
+    it "aliases reporter to author" do
+      expect(subject.author).to be(subject.reporter)
+    end
   end
 
   describe 'validations' do
diff --git a/spec/models/concerns/cache_markdown_field_spec.rb b/spec/models/concerns/cache_markdown_field_spec.rb
new file mode 100644
index 00000000000..15cd3a7ed70
--- /dev/null
+++ b/spec/models/concerns/cache_markdown_field_spec.rb
@@ -0,0 +1,181 @@
+require 'spec_helper'
+
+describe CacheMarkdownField do
+  CacheMarkdownField::CACHING_CLASSES << "ThingWithMarkdownFields"
+
+  # The minimum necessary ActiveModel to test this concern
+  class ThingWithMarkdownFields
+    include ActiveModel::Model
+    include ActiveModel::Dirty
+
+    include ActiveModel::Serialization
+
+    class_attribute :attribute_names
+    self.attribute_names = []
+
+    def attributes
+      attribute_names.each_with_object({}) do |name, hsh|
+        hsh[name.to_s] = send(name)
+      end
+    end
+
+    extend ActiveModel::Callbacks
+    define_model_callbacks :save
+
+    include CacheMarkdownField
+    cache_markdown_field :foo
+    cache_markdown_field :baz, pipeline: :single_line
+
+    def self.add_attr(attr_name)
+      self.attribute_names += [attr_name]
+      define_attribute_methods(attr_name)
+      attr_reader(attr_name)
+      define_method("#{attr_name}=") do |val|
+        send("#{attr_name}_will_change!") unless val == send(attr_name)
+        instance_variable_set("@#{attr_name}", val)
+      end
+    end
+
+    [:foo, :foo_html, :bar, :baz, :baz_html].each do |attr_name|
+      add_attr(attr_name)
+    end
+
+    def initialize(*)
+      super
+
+      # Pretend new is load
+      clear_changes_information
+    end
+
+    def save
+      run_callbacks :save do
+        changes_applied
+      end
+    end
+  end
+
+  CacheMarkdownField::CACHING_CLASSES.delete("ThingWithMarkdownFields")
+
+  def thing_subclass(new_attr)
+    Class.new(ThingWithMarkdownFields) { add_attr(new_attr) }
+  end
+
+  let(:markdown) { "`Foo`" }
+  let(:html) { "<p><code>Foo</code></p>" }
+
+  let(:updated_markdown) { "`Bar`" }
+  let(:updated_html) { "<p><code>Bar</code></p>" }
+
+  subject { ThingWithMarkdownFields.new(foo: markdown, foo_html: html) }
+
+  describe ".attributes" do
+    it "excludes cache attributes" do
+      expect(thing_subclass(:qux).new.attributes.keys.sort).to eq(%w[bar baz foo qux])
+    end
+  end
+
+  describe ".cache_markdown_field" do
+    it "refuses to allow untracked classes" do
+      expect { thing_subclass(:qux).__send__(:cache_markdown_field, :qux) }.to raise_error(RuntimeError)
+    end
+  end
+
+  context "an unchanged markdown field" do
+    before do
+      subject.foo = subject.foo
+      subject.save
+    end
+
+    it { expect(subject.foo).to eq(markdown) }
+    it { expect(subject.foo_html).to eq(html) }
+    it { expect(subject.foo_html_changed?).not_to be_truthy }
+  end
+
+  context "a changed markdown field" do
+    before do
+      subject.foo = updated_markdown
+      subject.save
+    end
+
+    it { expect(subject.foo_html).to eq(updated_html) }
+  end
+
+  context "a non-markdown field changed" do
+    before do
+      subject.bar = "OK"
+      subject.save
+    end
+
+    it { expect(subject.bar).to eq("OK") }
+    it { expect(subject.foo).to eq(markdown) }
+    it { expect(subject.foo_html).to eq(html) }
+  end
+
+  describe '#banzai_render_context' do
+    it "sets project to nil if the object lacks a project" do
+      context = subject.banzai_render_context(:foo)
+      expect(context).to have_key(:project)
+      expect(context[:project]).to be_nil
+    end
+
+    it "excludes author if the object lacks an author" do
+      context = subject.banzai_render_context(:foo)
+      expect(context).not_to have_key(:author)
+    end
+
+    it "raises if the context for an unrecognised field is requested" do
+      expect{subject.banzai_render_context(:not_found)}.to raise_error(ArgumentError)
+    end
+
+    it "includes the pipeline" do
+      context = subject.banzai_render_context(:baz)
+      expect(context[:pipeline]).to eq(:single_line)
+    end
+
+    it "returns copies of the context template" do
+      template = subject.cached_markdown_fields[:baz]
+      copy = subject.banzai_render_context(:baz)
+      expect(copy).not_to be(template)
+    end
+
+    context "with a project" do
+      subject { thing_subclass(:project).new(foo: markdown, foo_html: html, project: :project) }
+
+      it "sets the project in the context" do
+        context = subject.banzai_render_context(:foo)
+        expect(context).to have_key(:project)
+        expect(context[:project]).to eq(:project)
+      end
+
+      it "invalidates the cache when project changes" do
+        subject.project = :new_project
+        allow(Banzai::Renderer).to receive(:cacheless_render_field).and_return(updated_html)
+
+        subject.save
+
+        expect(subject.foo_html).to eq(updated_html)
+        expect(subject.baz_html).to eq(updated_html)
+      end
+    end
+
+    context "with an author" do
+      subject { thing_subclass(:author).new(foo: markdown, foo_html: html, author: :author) }
+
+      it "sets the author in the context" do
+        context = subject.banzai_render_context(:foo)
+        expect(context).to have_key(:author)
+        expect(context[:author]).to eq(:author)
+      end
+
+      it "invalidates the cache when author changes" do
+        subject.author = :new_author
+        allow(Banzai::Renderer).to receive(:cacheless_render_field).and_return(updated_html)
+
+        subject.save
+
+        expect(subject.foo_html).to eq(updated_html)
+        expect(subject.baz_html).to eq(updated_html)
+      end
+    end
+  end
+end
diff --git a/spec/models/project_spec.rb b/spec/models/project_spec.rb
index e52d4aaf884..381d14ed21a 100644
--- a/spec/models/project_spec.rb
+++ b/spec/models/project_spec.rb
@@ -518,7 +518,7 @@ describe Project, models: true do
   end
 
   describe '#cache_has_external_issue_tracker' do
-    let(:project) { create(:project) }
+    let(:project) { create(:project, has_external_issue_tracker: nil) }
 
     it 'stores true if there is any external_issue_tracker' do
       services = double(:service, external_issue_trackers: [RedmineService.new])
diff --git a/spec/models/service_spec.rb b/spec/models/service_spec.rb
index ed1bc9271ae..43937a54b2c 100644
--- a/spec/models/service_spec.rb
+++ b/spec/models/service_spec.rb
@@ -238,7 +238,7 @@ describe Service, models: true do
       it "updates the has_external_issue_tracker boolean" do
         expect do
           service.save!
-        end.to change { service.project.has_external_issue_tracker }.from(nil).to(true)
+        end.to change { service.project.has_external_issue_tracker }.from(false).to(true)
       end
     end
 
diff --git a/spec/models/snippet_spec.rb b/spec/models/snippet_spec.rb
index e6bc5296398..f62f6bacbaa 100644
--- a/spec/models/snippet_spec.rb
+++ b/spec/models/snippet_spec.rb
@@ -46,6 +46,13 @@ describe Snippet, models: true do
     end
   end
 
+  describe "#content_html_invalidated?" do
+    let(:snippet) { create(:snippet, content: "md", content_html: "html", file_name: "foo.md") }
+    it "invalidates the HTML cache of content when the filename changes" do
+      expect { snippet.file_name = "foo.rb" }.to change { snippet.content_html_invalidated? }.from(false).to(true)
+    end
+  end
+
   describe '.search' do
     let(:snippet) { create(:snippet) }
 
diff --git a/spec/requests/api/projects_spec.rb b/spec/requests/api/projects_spec.rb
index 4a0d727faea..861eb12b94c 100644
--- a/spec/requests/api/projects_spec.rb
+++ b/spec/requests/api/projects_spec.rb
@@ -232,7 +232,7 @@ describe API::API, api: true  do
       post api('/projects', user), project
 
       project.each_pair do |k, v|
-        next if %i{ issues_enabled merge_requests_enabled wiki_enabled }.include?(k)
+        next if %i[has_external_issue_tracker issues_enabled merge_requests_enabled wiki_enabled].include?(k)
         expect(json_response[k.to_s]).to eq(v)
       end
 
@@ -360,7 +360,7 @@ describe API::API, api: true  do
       post api("/projects/user/#{user.id}", admin), project
 
       project.each_pair do |k, v|
-        next if k == :path
+        next if %i[has_external_issue_tracker path].include?(k)
         expect(json_response[k.to_s]).to eq(v)
       end
     end
diff --git a/spec/services/git_push_service_spec.rb b/spec/services/git_push_service_spec.rb
index 22991c5bc86..8e3e12114f2 100644
--- a/spec/services/git_push_service_spec.rb
+++ b/spec/services/git_push_service_spec.rb
@@ -448,6 +448,8 @@ describe GitPushService, services: true do
       let(:jira_tracker) { project.create_jira_service if project.jira_service.nil? }
 
       before do
+        # project.create_jira_service doesn't seem to invalidate the cache here
+        project.has_external_issue_tracker = true
         jira_service_settings
 
         WebMock.stub_request(:post, jira_api_transition_url)
diff --git a/spec/services/merge_requests/merge_service_spec.rb b/spec/services/merge_requests/merge_service_spec.rb
index e49a0d5e553..ee53e110aee 100644
--- a/spec/services/merge_requests/merge_service_spec.rb
+++ b/spec/services/merge_requests/merge_service_spec.rb
@@ -60,7 +60,10 @@ describe MergeRequests::MergeService, services: true do
 
         let(:jira_tracker) { project.create_jira_service }
 
-        before { jira_service_settings }
+        before do
+          project.update_attributes!(has_external_issue_tracker: true)
+          jira_service_settings
+        end
 
         it 'closes issues on JIRA issue tracker' do
           jira_issue = ExternalIssue.new('JIRA-123', project)
diff --git a/spec/services/system_note_service_spec.rb b/spec/services/system_note_service_spec.rb
index d1a47ea9b6f..304d4e62396 100644
--- a/spec/services/system_note_service_spec.rb
+++ b/spec/services/system_note_service_spec.rb
@@ -531,12 +531,12 @@ describe SystemNoteService, services: true do
   include JiraServiceHelper
 
   describe 'JIRA integration' do
-    let(:project)    { create(:project) }
+    let(:project)    { create(:jira_project) }
     let(:author)     { create(:user) }
     let(:issue)      { create(:issue, project: project) }
     let(:mergereq)   { create(:merge_request, :simple, target_project: project, source_project: project) }
     let(:jira_issue) { ExternalIssue.new("JIRA-1", project)}
-    let(:jira_tracker) { project.create_jira_service if project.jira_service.nil? }
+    let(:jira_tracker) { project.jira_service }
     let(:commit)     { project.commit }
 
     context 'in JIRA issue tracker' do
@@ -545,10 +545,6 @@ describe SystemNoteService, services: true do
         WebMock.stub_request(:post, jira_api_comment_url)
       end
 
-      after do
-        jira_tracker.destroy!
-      end
-
       describe "new reference" do
         before do
           WebMock.stub_request(:get, jira_api_comment_url).to_return(body: jira_issue_comments)
@@ -578,10 +574,6 @@ describe SystemNoteService, services: true do
           WebMock.stub_request(:get, jira_api_comment_url).to_return(body: jira_issue_comments)
         end
 
-        after do
-          jira_tracker.destroy!
-        end
-
         subject { described_class.cross_reference(jira_issue, issue, author) }
 
         it { is_expected.to eq(jira_status_message) }