Migrate events into a new format

This commit migrates events data in such a way that push events are
stored much more efficiently. This is done by creating a shadow table
called "events_for_migration", and a table called "push_event_payloads"
which is used for storing push data of push events. The background
migration in this commit will copy events from the "events" table into
the "events_for_migration" table, push events in will also have a row
created in "push_event_payloads".

This approach allows us to reclaim space in the next release by simply
swapping the "events" and "events_for_migration" tables, then dropping
the old events (now "events_for_migration") table.

The new table structure is also optimised for storage space, and does
not include the unused "title" column nor the "data" column (since this
data is moved to "push_event_payloads").

== Newly Created Events

Newly created events are inserted into both "events" and
"events_for_migration", both using the exact same primary key value. The
table "push_event_payloads" in turn has a foreign key to the _shadow_
table. This removes the need for recreating and validating the foreign
key after swapping the tables. Since the shadow table also has a foreign
key to "projects.id" we also don't have to worry about orphaned rows.

This approach however does require some additional storage as we're
duplicating a portion of the events data for at least 1 release. The
exact amount is hard to estimate, but for GitLab.com this is expected to
be between 10 and 20 GB at most. The background migration in this commit
deliberately does _not_ update the "events" table as doing so would put
a lot of pressure on PostgreSQL's auto vacuuming system.

== Supporting Both Old And New Events

Application code has also been adjusted to support push events using
both the old and new data formats. This is done by creating a PushEvent
class which extends the regular Event class. Using Rails' Single Table
Inheritance system we can ensure the right class is used for the right
data, which in this case is based on the value of `events.action`. To
support displaying old and new data at the same time the PushEvent class
re-defines a few methods of the Event class, falling back to their
original implementations for push events in the old format.

Once all existing events have been migrated the various push event
related methods can be removed from the Event model, and the calls to
`super` can be removed from the methods in the PushEvent model.

The UI and event atom feed have also been slightly changed to better
handle this new setup, fortunately only a few changes were necessary to
make this work.

== API Changes

The API only displays push data of events in the new format. Supporting
both formats in the API is a bit more difficult compared to the UI.
Since the old push data was not really well documented (apart from one
example that used an incorrect "action" nmae) I decided that supporting
both was not worth the effort, especially since events will be migrated
in a few days _and_ new events are created in the correct format.

app/models/event.rb

@@ -48,6 +48,7 @@ class Event < ActiveRecord::Base
   belongs_to :author, class_name: "User"
   belongs_to :project
   belongs_to :target, polymorphic: true # rubocop:disable Cop/PolymorphicAssociations
+  has_one :push_event_payload, foreign_key: :event_id
   # For Hash only
   serialize :data # rubocop:disable Cop/ActiveRecordSerialize
@@ -55,6 +56,7 @@ class Event < ActiveRecord::Base
   # Callbacks
   after_create :reset_project_activity
   after_create :set_last_repository_updated_at, if: :push?
+  after_create :replicate_event_for_push_events_migration
   # Scopes
   scope :recent, -> { reorder(id: :desc) }
@@ -64,10 +66,36 @@ class Event < ActiveRecord::Base
     where(project_id: projects.pluck(:id)).recent
   end
-  scope :with_associations, -> { includes(:author, :project, project: :namespace).preload(:target) }
+  scope :with_associations, -> do
+    # We're using preload for "push_event_payload" as otherwise the association
+    # is not always available (depending on the query being built).
+    includes(:author, :project, project: :namespace)
+      .preload(:target, :push_event_payload)
+  end
+
   scope :for_milestone_id, ->(milestone_id) { where(target_type: "Milestone", target_id: milestone_id) }
+  self.inheritance_column = 'action'
+
   class << self
+    def find_sti_class(action)
+      if action.to_i == PUSHED
+        PushEvent
+      else
+        Event
+      end
+    end
+
+    def subclass_from_attributes(attrs)
+      # Without this Rails will keep calling this method on the returned class,
+      # resulting in an infinite loop.
+      return unless self == Event
+
+      action = attrs.with_indifferent_access[inheritance_column].to_i
+
+      PushEvent if action == PUSHED
+    end
+
     # Update Gitlab::ContributionsCalendar#activity_dates if this changes
     def contributions
       where("action = ? OR (target_type IN (?) AND action IN (?)) OR (target_type = ? AND action = ?)",
@@ -290,6 +318,16 @@ class Event < ActiveRecord::Base
     @commits ||= (data[:commits] || []).reverse
   end
+  def commit_title
+    commit = commits.last
+
+    commit[:message] if commit
+  end
+
+  def commit_id
+    commit_to || commit_from
+  end
+
   def commits_count
     data[:total_commits_count] || commits.count || 0
   end
@@ -385,6 +423,16 @@ class Event < ActiveRecord::Base
     user ? author_id == user.id : false
   end
+  # We're manually replicating data into the new table since database triggers
+  # are not dumped to db/schema.rb. This could mean that a new installation
+  # would not have the triggers in place, thus losing events data in GitLab
+  # 10.0.
+  def replicate_event_for_push_events_migration
+    new_attributes = attributes.with_indifferent_access.except(:title, :data)
+
+    EventForMigration.create!(new_attributes)
+  end
+
   private
   def recent_update?

app/models/event_for_migration.rb

+# This model is used to replicate events between the old "events" table and the
+# new "events_for_migration" table that will replace "events" in GitLab 10.0.
+class EventForMigration < ActiveRecord::Base
+  self.table_name = 'events_for_migration'
+end

app/models/push_event.rb

+class PushEvent < Event
+  # This validation exists so we can't accidentally use PushEvent with a
+  # different "action" value.
+  validate :validate_push_action
+
+  # Authors are required as they're used to display who pushed data.
+  #
+  # We're just validating the presence of the ID here as foreign key constraints
+  # should ensure the ID points to a valid user.
+  validates :author_id, presence: true
+
+  # The project is required to build links to commits, commit ranges, etc.
+  #
+  # We're just validating the presence of the ID here as foreign key constraints
+  # should ensure the ID points to a valid project.
+  validates :project_id, presence: true
+
+  # The "data" field must not be set for push events since it's not used and a
+  # waste of space.
+  validates :data, absence: true
+
+  # These fields are also not used for push events, thus storing them would be a
+  # waste.
+  validates :target_id, absence: true
+  validates :target_type, absence: true
+
+  def self.sti_name
+    PUSHED
+  end
+
+  def push?
+    true
+  end
+
+  def push_with_commits?
+    !!(commit_from && commit_to)
+  end
+
+  def tag?
+    return super unless push_event_payload
+
+    push_event_payload.tag?
+  end
+
+  def branch?
+    return super unless push_event_payload
+
+    push_event_payload.branch?
+  end
+
+  def valid_push?
+    return super unless push_event_payload
+
+    push_event_payload.ref.present?
+  end
+
+  def new_ref?
+    return super unless push_event_payload
+
+    push_event_payload.created?
+  end
+
+  def rm_ref?
+    return super unless push_event_payload
+
+    push_event_payload.removed?
+  end
+
+  def commit_from
+    return super unless push_event_payload
+
+    push_event_payload.commit_from
+  end
+
+  def commit_to
+    return super unless push_event_payload
+
+    push_event_payload.commit_to
+  end
+
+  def ref_name
+    return super unless push_event_payload
+
+    push_event_payload.ref
+  end
+
+  def ref_type
+    return super unless push_event_payload
+
+    push_event_payload.ref_type
+  end
+
+  def branch_name
+    return super unless push_event_payload
+
+    ref_name
+  end
+
+  def tag_name
+    return super unless push_event_payload
+
+    ref_name
+  end
+
+  def commit_title
+    return super unless push_event_payload
+
+    push_event_payload.commit_title
+  end
+
+  def commit_id
+    commit_to || commit_from
+  end
+
+  def commits_count
+    return super unless push_event_payload
+
+    push_event_payload.commit_count
+  end
+
+  def validate_push_action
+    return if action == PUSHED
+
+    errors.add(:action, "the action #{action.inspect} is not valid")
+  end
+end

app/models/push_event_payload.rb

+class PushEventPayload < ActiveRecord::Base
+  include ShaAttribute
+
+  belongs_to :event, inverse_of: :push_event_payload
+
+  validates :event_id, :commit_count, :action, :ref_type, presence: true
+  validates :commit_title, length: { maximum: 70 }
+
+  sha_attribute :commit_from
+  sha_attribute :commit_to
+
+  enum action: {
+    created: 0,
+    removed: 1,
+    pushed: 2
+  }
+
+  enum ref_type: {
+    branch: 0,
+    tag: 1
+  }
+end

app/services/event_create_service.rb

@@ -71,7 +71,14 @@ class EventCreateService
   end
   def push(project, current_user, push_data)
-    create_event(project, current_user, Event::PUSHED, data: push_data)
+    # We're using an explicit transaction here so that any errors that may occur
+    # when creating push payload data will result in the event creation being
+    # rolled back as well.
+    Event.transaction do
+      event = create_event(project, current_user, Event::PUSHED)
+
+      PushEventPayloadService.new(event, push_data).execute
+    end
     Users::ActivityService.new(current_user, 'push').execute
   end

app/services/push_event_payload_service.rb

+# Service class for creating push event payloads as stored in the
+# "push_event_payloads" table.
+#
+# Example:
+#
+#     data = Gitlab::DataBuilder::Push.build(...)
+#     event = Event.create(...)
+#
+#     PushEventPayloadService.new(event, data).execute
+class PushEventPayloadService
+  # event - The event this push payload belongs to.
+  # push_data - A Hash produced by `Gitlab::DataBuilder::Push.build` to use for
+  #             building the push payload.
+  def initialize(event, push_data)
+    @event = event
+    @push_data = push_data
+  end
+
+  # Creates and returns a new PushEventPayload row.
+  #
+  # This method will raise upon encountering validation errors.
+  #
+  # Returns an instance of PushEventPayload.
+  def execute
+    @event.build_push_event_payload(
+      commit_count: commit_count,
+      action: action,
+      ref_type: ref_type,
+      commit_from: commit_from_id,
+      commit_to: commit_to_id,
+      ref: trimmed_ref,
+      commit_title: commit_title,
+      event_id: @event.id
+    )
+
+    @event.push_event_payload.save!
+    @event.push_event_payload
+  end
+
+  # Returns the commit title to use.
+  #
+  # The commit title is limited to the first line and a maximum of 70
+  # characters.
+  def commit_title
+    commit = @push_data.fetch(:commits).last
+
+    return nil unless commit && commit[:message]
+
+    raw_msg = commit[:message]
+
+    # Find where the first line ends, without turning the entire message into an
+    # Array of lines (this is a waste of memory for large commit messages).
+    index = raw_msg.index("\n")
+    message = index ? raw_msg[0..index] : raw_msg
+
+    message.strip.truncate(70)
+  end
+
+  def commit_from_id
+    if create?
+      nil
+    else
+      revision_before
+    end
+  end
+
+  def commit_to_id
+    if remove?
+      nil
+    else
+      revision_after
+    end
+  end
+
+  def commit_count
+    @push_data.fetch(:total_commits_count)
+  end
+
+  def ref
+    @push_data.fetch(:ref)
+  end
+
+  def revision_before
+    @push_data.fetch(:before)
+  end
+
+  def revision_after
+    @push_data.fetch(:after)
+  end
+
+  def trimmed_ref
+    Gitlab::Git.ref_name(ref)
+  end
+
+  def create?
+    Gitlab::Git.blank_ref?(revision_before)
+  end
+
+  def remove?
+    Gitlab::Git.blank_ref?(revision_after)
+  end
+
+  def action
+    if create?
+      :created
+    elsif remove?
+      :removed
+    else
+      :pushed
+    end
+  end
+
+  def ref_type
+    if Gitlab::Git.tag_ref?(ref)
+      :tag
+    else
+      :branch
+    end
+  end
+end

app/views/events/_commit.html.haml

 %li.commit
   .commit-row-title
-    = link_to truncate_sha(commit[:id]), project_commit_path(project, commit[:id]), class: "commit-sha", alt: '', title: truncate_sha(commit[:id])
+    = link_to truncate_sha(event.commit_id), project_commit_path(project, event.commit_id), class: "commit-sha", alt: '', title: truncate_sha(event.commit_id)
     ·
-    = markdown event_commit_title(commit[:message]), project: project, pipeline: :single_line, author: event.author
+    = markdown event_commit_title(event.commit_title), project: project, pipeline: :single_line, author: event.author

app/views/events/_event_push.atom.haml

 %div{ xmlns: "http://www.w3.org/1999/xhtml" }
-  - event.commits.first(15).each do |commit|
-    %p
-      %strong= commit[:author][:name]
-      = link_to "(##{truncate_sha(commit[:id])})", project_commit_path(event.project, id: commit[:id])
-      %i
-        at
-        = commit[:timestamp].to_time.to_s(:short)
-    %blockquote= markdown(escape_once(commit[:message]), pipeline: :atom, project: event.project, author: event.author)
-  - if event.commits_count > 15
+  %p
+    %strong= event.author_name
+    = link_to "(#{truncate_sha(event.commit_id)})", project_commit_path(event.project, event.commit_id)
+    %i
+      at
+      = event.created_at.to_s(:short)
+  %blockquote= markdown(escape_once(event.commit_title), pipeline: :atom, project: event.project, author: event.author)
+  - if event.commits_count > 1
     %p
       %i
         \... and
-        = pluralize(event.commits_count - 15, "more commit")
+        = pluralize(event.commits_count - 1, "more commit")

app/views/events/event/_push.html.haml

@@ -14,9 +14,7 @@
 - if event.push_with_commits?
   .event-body
     %ul.well-list.event_commits
-      - few_commits = event.commits[0...2]
-      - few_commits.each do |commit|
-        = render "events/commit", commit: commit, project: project, event: event
+      = render "events/commit", project: project, event: event
       - create_mr = event.new_ref? && create_mr_button?(project.default_branch, event.ref_name, project) && event.authored_by?(current_user)
       - if event.commits_count > 1
@@ -44,9 +42,6 @@
           = link_to create_mr_path(project.default_branch, event.ref_name, project) do
             Create Merge Request
 - elsif event.rm_ref?
-  - repository = project.repository
-  - last_commit = repository.commit(event.commit_from)
-  - if last_commit
-    .event-body
-      %ul.well-list.event_commits
-        = render "events/commit", commit: last_commit, project: project, event: event
+  .event-body
+    %ul.well-list.event_commits
+      = render "events/commit", project: project, event: event

changelogs/unreleased/migrate-events-into-a-new-format.yml

+---
+title: Migrate events into a new format to reduce the storage necessary and improve performance
+merge_request:
+author:

db/migrate/20170608152747_prepare_events_table_for_push_events_migration.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class PrepareEventsTableForPushEventsMigration < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    # The order of these columns is deliberate and results in the following
+    # columns and sizes:
+    #
+    # * id (4 bytes)
+    # * project_id (4 bytes)
+    # * author_id (4 bytes)
+    # * target_id (4 bytes)
+    # * created_at (8 bytes)
+    # * updated_at (8 bytes)
+    # * action (2 bytes)
+    # * target_type (variable)
+    #
+    # Unfortunately we can't make the "id" column a bigint/bigserial as Rails 4
+    # does not support this properly.
+    create_table :events_for_migration do |t|
+      t.references :project,
+                   index: true,
+                   foreign_key: { on_delete: :cascade }
+
+      t.integer :author_id, index: true, null: false
+      t.integer :target_id
+
+      t.timestamps_with_timezone null: false
+
+      t.integer :action, null: false, limit: 2, index: true
+      t.string :target_type
+
+      t.index %i[target_type target_id]
+    end
+
+    # t.references doesn't like it when the column name doesn't make the table
+    # name so we have to add the foreign key separately.
+    add_concurrent_foreign_key(:events_for_migration, :users, column: :author_id)
+  end
+
+  def down
+    drop_table :events_for_migration
+  end
+end

db/migrate/20170608152748_create_push_event_payloads_tables.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class CreatePushEventPayloadsTables < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    create_table :push_event_payloads, id: false do |t|
+      t.bigint :commit_count, null: false
+
+      t.integer :event_id, null: false
+      t.integer :action, null: false, limit: 2
+      t.integer :ref_type, null: false, limit: 2
+
+      t.binary :commit_from
+      t.binary :commit_to
+
+      t.text :ref
+      t.string :commit_title, limit: 70
+
+      t.index :event_id, unique: true
+    end
+
+    # We're adding a foreign key to the _shadow_ table, and this is deliberate.
+    # By using the shadow table we don't have to recreate/revalidate this
+    # foreign key after swapping the "events_for_migration" and "events" tables.
+    #
+    # The "events_for_migration" table has a foreign key to "projects.id"
+    # ensuring that project removals also remove events from the shadow table
+    # (and thus also from this table).
+    add_concurrent_foreign_key(
+      :push_event_payloads,
+      :events_for_migration,
+      column: :event_id
+    )
+  end
+
+  def down
+    drop_table :push_event_payloads
+  end
+end

db/post_migrate/20170627101016_schedule_event_migrations.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class ScheduleEventMigrations < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  BUFFER_SIZE = 1000
+
+  disable_ddl_transaction!
+
+  class Event < ActiveRecord::Base
+    include EachBatch
+
+    self.table_name = 'events'
+  end
+
+  def up
+    jobs = []
+
+    Event.each_batch(of: 1000) do |relation|
+      min, max = relation.pluck('MIN(id), MAX(id)').first
+
+      if jobs.length == BUFFER_SIZE
+        # We push multiple jobs at a time to reduce the time spent in
+        # Sidekiq/Redis operations. We're using this buffer based approach so we
+        # don't need to run additional queries for every range.
+        BackgroundMigrationWorker.perform_bulk(jobs)
+        jobs.clear
+      end
+
+      jobs << ['MigrateEventsToPushEventPayloads', [min, max]]
+    end
+
+    BackgroundMigrationWorker.perform_bulk(jobs) unless jobs.empty?
+  end
+
+  def down
+  end
+end

db/schema.rb

@@ -534,6 +534,21 @@ ActiveRecord::Schema.define(version: 20170807160457) do
   add_index "events", ["target_id"], name: "index_events_on_target_id", using: :btree
   add_index "events", ["target_type"], name: "index_events_on_target_type", using: :btree
+  create_table "events_for_migration", force: :cascade do |t|
+    t.integer "project_id"
+    t.integer "author_id", null: false
+    t.integer "target_id"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.integer "action", limit: 2, null: false
+    t.string "target_type"
+  end
+
+  add_index "events_for_migration", ["action"], name: "index_events_for_migration_on_action", using: :btree
+  add_index "events_for_migration", ["author_id"], name: "index_events_for_migration_on_author_id", using: :btree
+  add_index "events_for_migration", ["project_id"], name: "index_events_for_migration_on_project_id", using: :btree
+  add_index "events_for_migration", ["target_type", "target_id"], name: "index_events_for_migration_on_target_type_and_target_id", using: :btree
+
   create_table "feature_gates", force: :cascade do |t|
     t.string "feature_key", null: false
     t.string "key", null: false
@@ -1254,6 +1269,19 @@ ActiveRecord::Schema.define(version: 20170807160457) do
   add_index "protected_tags", ["project_id"], name: "index_protected_tags_on_project_id", using: :btree
+  create_table "push_event_payloads", id: false, force: :cascade do |t|
+    t.integer "commit_count", limit: 8, null: false
+    t.integer "event_id", null: false
+    t.integer "action", limit: 2, null: false
+    t.integer "ref_type", limit: 2, null: false
+    t.binary "commit_from"
+    t.binary "commit_to"
+    t.text "ref"
+    t.string "commit_title", limit: 70
+  end
+
+  add_index "push_event_payloads", ["event_id"], name: "index_push_event_payloads_on_event_id", unique: true, using: :btree
+
   create_table "redirect_routes", force: :cascade do |t|
     t.integer "source_id", null: false
     t.string "source_type", null: false
@@ -1654,6 +1682,8 @@ ActiveRecord::Schema.define(version: 20170807160457) do
   add_foreign_key "deployments", "projects", name: "fk_b9a3851b82", on_delete: :cascade
   add_foreign_key "environments", "projects", name: "fk_d1c8c1da6a", on_delete: :cascade
   add_foreign_key "events", "projects", name: "fk_0434b48643", on_delete: :cascade
+  add_foreign_key "events_for_migration", "projects", on_delete: :cascade
+  add_foreign_key "events_for_migration", "users", column: "author_id", name: "fk_edfd187b6f", on_delete: :cascade
   add_foreign_key "forked_project_links", "projects", column: "forked_to_project_id", name: "fk_434510edb0", on_delete: :cascade
   add_foreign_key "gpg_keys", "users", on_delete: :cascade
   add_foreign_key "gpg_signatures", "gpg_keys", on_delete: :nullify
@@ -1696,6 +1726,7 @@ ActiveRecord::Schema.define(version: 20170807160457) do
   add_foreign_key "protected_tag_create_access_levels", "protected_tags"
   add_foreign_key "protected_tag_create_access_levels", "users"
   add_foreign_key "protected_tags", "projects", name: "fk_8e4af87648", on_delete: :cascade
+  add_foreign_key "push_event_payloads", "events_for_migration", column: "event_id", name: "fk_36c74129da", on_delete: :cascade
   add_foreign_key "releases", "projects", name: "fk_47fe2a0596", on_delete: :cascade
   add_foreign_key "services", "projects", name: "fk_71cce407f9", on_delete: :cascade
   add_foreign_key "snippets", "projects", name: "fk_be41fd4bb7", on_delete: :cascade

doc/api/events.md

@@ -79,7 +79,6 @@ Example response:
     "target_id":160,
     "target_type":"Issue",
     "author_id":25,
-    "data":null,
     "target_title":"Qui natus eos odio tempore et quaerat consequuntur ducimus cupiditate quis.",
     "created_at":"2017-02-09T10:43:19.667Z",
     "author":{
@@ -99,7 +98,6 @@ Example response:
     "target_id":159,
     "target_type":"Issue",
     "author_id":21,
-    "data":null,
     "target_title":"Nostrum enim non et sed optio illo deleniti non.",
     "created_at":"2017-02-09T10:43:19.426Z",
     "author":{
@@ -151,7 +149,6 @@ Example response:
     "target_id": 830,
     "target_type": "Issue",
     "author_id": 1,
-    "data": null,
     "target_title": "Public project search field",
     "author": {
       "name": "Dmitriy Zaporozhets",
@@ -166,7 +163,7 @@ Example response:
   {
     "title": null,
     "project_id": 15,
-    "action_name": "opened",
+    "action_name": "pushed",
     "target_id": null,
     "target_type": null,
     "author_id": 1,
@@ -179,31 +176,14 @@ Example response:
       "web_url": "http://localhost:3000/root"
     },
     "author_username": "john",
-    "data": {
-      "before": "50d4420237a9de7be1304607147aec22e4a14af7",
-      "after": "c5feabde2d8cd023215af4d2ceeb7a64839fc428",
-      "ref": "refs/heads/master",
-      "user_id": 1,
-      "user_name": "Dmitriy Zaporozhets",
-      "repository": {
-        "name": "gitlabhq",
-        "url": "git@dev.gitlab.org:gitlab/gitlabhq.git",
-        "description": "GitLab: self hosted Git management software. \r\nDistributed under the MIT License.",
-        "homepage": "https://dev.gitlab.org/gitlab/gitlabhq"
-      },
-      "commits": [
-        {
-          "id": "c5feabde2d8cd023215af4d2ceeb7a64839fc428",
-          "message": "Add simple search to projects in public area",
-          "timestamp": "2013-05-13T18:18:08+00:00",
-          "url": "https://dev.gitlab.org/gitlab/gitlabhq/commit/c5feabde2d8cd023215af4d2ceeb7a64839fc428",
-          "author": {
-            "name": "Dmitriy Zaporozhets",
-            "email": "dmitriy.zaporozhets@gmail.com"
-          }
-        }
-      ],
-      "total_commits_count": 1
+    "push_data": {
+      "commit_count": 1,
+      "action": "pushed",
+      "ref_type": "branch",
+      "commit_from": "50d4420237a9de7be1304607147aec22e4a14af7",
+      "commit_to": "c5feabde2d8cd023215af4d2ceeb7a64839fc428",
+      "ref": "master",
+      "commit_title": "Add simple search to projects in public area"
     },
     "target_title": null
   },
@@ -214,7 +194,6 @@ Example response:
     "target_id": 840,
     "target_type": "Issue",
     "author_id": 1,
-    "data": null,
     "target_title": "Finish & merge Code search PR",
     "author": {
       "name": "Dmitriy Zaporozhets",
@@ -233,7 +212,6 @@ Example response:
     "target_id": 1312,
     "target_type": "Note",
     "author_id": 1,
-    "data": null,
     "target_title": null,
     "created_at": "2015-12-04T10:33:58.089Z",
     "note": {
@@ -305,7 +283,6 @@ Example response:
     "target_iid":160,
     "target_type":"Issue",
     "author_id":25,
-    "data":null,
     "target_title":"Qui natus eos odio tempore et quaerat consequuntur ducimus cupiditate quis.",
     "created_at":"2017-02-09T10:43:19.667Z",
     "author":{
@@ -326,7 +303,6 @@ Example response:
     "target_iid":159,
     "target_type":"Issue",
     "author_id":21,
-    "data":null,
     "target_title":"Nostrum enim non et sed optio illo deleniti non.",
     "created_at":"2017-02-09T10:43:19.426Z",
     "author":{

features/steps/shared/project.rb

@@ -71,28 +71,14 @@ module SharedProject
   step 'project "Shop" has push event' do
     @project = Project.find_by(name: "Shop")
-
-    data = {
-      before: Gitlab::Git::BLANK_SHA,
-      after: "6d394385cf567f80a8fd85055db1ab4c5295806f",
-      ref: "refs/heads/fix",
-      user_id: @user.id,
-      user_name: @user.name,
-      repository: {
-        name: @project.name,
-        url: "localhost/rubinius",
-        description: "",
-        homepage: "localhost/rubinius",
-        private: true
-      }
-    }
-
-    @event = Event.create(
-      project: @project,
-      action: Event::PUSHED,
-      data: data,
-      author_id: @user.id
-    )
+    @event = create(:push_event, project: @project, author: @user)
+
+    create(:push_event_payload,
+           event: @event,
+           action: :created,
+           commit_to: '6d394385cf567f80a8fd85055db1ab4c5295806f',
+           ref: 'fix',
+           commit_count: 1)
   end
   step 'I should see project "Shop" activity feed' do

lib/api/entities.rb

@@ -497,14 +497,24 @@ module API
       expose :author, using: Entities::UserBasic
     end
+    class PushEventPayload < Grape::Entity
+      expose :commit_count, :action, :ref_type, :commit_from, :commit_to
+      expose :ref, :commit_title
+    end
+
     class Event < Grape::Entity
       expose :title, :project_id, :action_name
       expose :target_id, :target_iid, :target_type, :author_id
-      expose :data, :target_title
+      expose :target_title
       expose :created_at
       expose :note, using: Entities::Note, if: ->(event, options) { event.note? }
       expose :author, using: Entities::UserBasic, if: ->(event, options) { event.author }
+      expose :push_event_payload,
+        as: :push_data,
+        using: PushEventPayload,
+        if: -> (event, _) { event.push? }
+
       expose :author_username do |event, options|
         event.author&.username
       end

lib/api/v3/entities.rb

@@ -25,14 +25,24 @@ module API
         expose(:downvote?)  { |note| false }
       end
+      class PushEventPayload < Grape::Entity
+        expose :commit_count, :action, :ref_type, :commit_from, :commit_to
+        expose :ref, :commit_title
+      end
+
       class Event < Grape::Entity
         expose :title, :project_id, :action_name
         expose :target_id, :target_type, :author_id
-        expose :data, :target_title
+        expose :target_title
         expose :created_at
         expose :note, using: Entities::Note, if: ->(event, options) { event.note? }
         expose :author, using: ::API::Entities::UserBasic, if: ->(event, options) { event.author }
+        expose :push_event_payload,
+          as: :push_data,
+          using: PushEventPayload,
+          if: -> (event, _) { event.push? }
+
         expose :author_username do |event, options|
           event.author&.username
         end

lib/gitlab/background_migration/migrate_events_to_push_event_payloads.rb

+module Gitlab
+  module BackgroundMigration
+    # Class that migrates events for the new push event payloads setup. All
+    # events are copied to a shadow table, and push events will also have a row
+    # created in the push_event_payloads table.
+    class MigrateEventsToPushEventPayloads
+      class Event < ActiveRecord::Base
+        self.table_name = 'events'
+
+        serialize :data
+
+        BLANK_REF = ('0' * 40).freeze
+        TAG_REF_PREFIX = 'refs/tags/'.freeze
+        MAX_INDEX = 69
+        PUSHED = 5
+
+        def push_event?
+          action == PUSHED && data.present?
+        end
+
+        def commit_title
+          commit = commits.last
+
+          return nil unless commit && commit[:message]
+
+          index = commit[:message].index("\n")
+          message = index ? commit[:message][0..index] : commit[:message]
+
+          message.strip.truncate(70)
+        end
+
+        def commit_from_sha
+          if create?
+            nil
+          else
+            data[:before]
+          end
+        end
+
+        def commit_to_sha
+          if remove?
+            nil
+          else
+            data[:after]
+          end
+        end
+
+        def data
+          super || {}
+        end
+
+        def commits
+          data[:commits] || []
+        end
+
+        def commit_count
+          data[:total_commits_count] || 0
+        end
+
+        def ref
+          data[:ref]
+        end
+
+        def trimmed_ref_name
+          if ref_type == :tag
+            ref[10..-1]
+          else
+            ref[11..-1]
+          end
+        end
+
+        def create?
+          data[:before] == BLANK_REF
+        end
+
+        def remove?
+          data[:after] == BLANK_REF
+        end
+
+        def push_action
+          if create?
+            :created
+          elsif remove?
+            :removed
+          else
+            :pushed
+          end
+        end
+
+        def ref_type
+          if ref.start_with?(TAG_REF_PREFIX)
+            :tag
+          else
+            :branch
+          end
+        end
+      end
+
+      class EventForMigration < ActiveRecord::Base
+        self.table_name = 'events_for_migration'
+      end
+
+      class PushEventPayload < ActiveRecord::Base
+        self.table_name = 'push_event_payloads'
+
+        enum action: {
+          created: 0,
+          removed: 1,
+          pushed: 2
+        }
+
+        enum ref_type: {
+          branch: 0,
+          tag: 1
+        }
+      end
+
+      # start_id - The start ID of the range of events to process
+      # end_id - The end ID of the range to process.
+      def perform(start_id, end_id)
+        return unless migrate?
+
+        find_events(start_id, end_id).each { |event| process_event(event) }
+      end
+
+      def process_event(event)
+        replicate_event(event)
+        create_push_event_payload(event) if event.push_event?
+      end
+
+      def replicate_event(event)
+        new_attributes = event.attributes
+          .with_indifferent_access.except(:title, :data)
+
+        EventForMigration.create!(new_attributes)
+      rescue ActiveRecord::InvalidForeignKey
+        # A foreign key error means the associated event was removed. In this
+        # case we'll just skip migrating the event.
+      end
+
+      def create_push_event_payload(event)
+        commit_from = pack(event.commit_from_sha)
+        commit_to = pack(event.commit_to_sha)
+
+        PushEventPayload.create!(
+          event_id: event.id,
+          commit_count: event.commit_count,
+          ref_type: event.ref_type,
+          action: event.push_action,
+          commit_from: commit_from,
+          commit_to: commit_to,
+          ref: event.trimmed_ref_name,
+          commit_title: event.commit_title
+        )
+      rescue ActiveRecord::InvalidForeignKey
+        # A foreign key error means the associated event was removed. In this
+        # case we'll just skip migrating the event.
+      end
+
+      def find_events(start_id, end_id)
+        Event
+          .where('NOT EXISTS (SELECT true FROM events_for_migration WHERE events_for_migration.id = events.id)')
+          .where(id: start_id..end_id)
+      end
+
+      def migrate?
+        Event.table_exists? && PushEventPayload.table_exists? &&
+          EventForMigration.table_exists?
+      end
+
+      def pack(value)
+        value ? [value].pack('H*') : nil
+      end
+    end
+  end
+end

lib/gitlab/import_export/import_export.yml

@@ -3,18 +3,22 @@ project_tree:
   - labels:
       :priorities
   - milestones:
-    - :events
+    - events:
+      - :push_event_payload
   - issues:
-    - :events
+    - events:
+      - :push_event_payload
     - :timelogs
     - notes:
       - :author
-      - :events
+      - events:
+        - :push_event_payload
     - label_links:
       - label:
           :priorities
     - milestone:
-      - :events
+      - events:
+        - :push_event_payload
   - snippets:
     - :award_emoji
     - notes:
@@ -25,21 +29,25 @@ project_tree:
   - merge_requests:
     - notes:
       - :author
-      - :events
+      - events:
+        - :push_event_payload
     - merge_request_diff:
       - :merge_request_diff_commits
       - :merge_request_diff_files
-    - :events
+    - events:
+      - :push_event_payload
     - :timelogs
     - label_links:
       - label:
           :priorities
     - milestone:
-      - :events
+      - events:
+        - :push_event_payload
   - pipelines:
     - notes:
       - :author
-      - :events
+      - events:
+        - :push_event_payload
     - :stages
     - :statuses
   - :triggers
@@ -107,6 +115,8 @@ excluded_attributes:
   statuses:
     - :trace
     - :token
+  push_event_payload:
+    - :event_id
 methods:
   labels: