Merge branch 'deduplicate-merge-request-diff-authors' into 'master'

Reduce space needed for merge request diff commits

See merge request gitlab-org/gitlab!63669

app/models/merge_request.rb

@@ -360,7 +360,7 @@ class MergeRequest < ApplicationRecord
   scope :preload_approved_by_users, -> { preload(:approved_by_users) }
   scope :preload_metrics, -> (relation) { preload(metrics: relation) }
   scope :preload_project_and_latest_diff, -> { preload(:source_project, :latest_merge_request_diff) }
-  scope :preload_latest_diff_commit, -> { preload(latest_merge_request_diff: :merge_request_diff_commits) }
+  scope :preload_latest_diff_commit, -> { preload(latest_merge_request_diff: { merge_request_diff_commits: [:commit_author, :committer] }) }
   scope :preload_milestoneish_associations, -> { preload_routables.preload(:assignees, :labels) }
 
   scope :with_web_entity_associations, -> { preload(:author, target_project: [:project_feature, group: [:route, :parent], namespace: :route]) }

app/models/merge_request/diff_commit_user.rb

+# frozen_string_literal: true
+
+class MergeRequest::DiffCommitUser < ApplicationRecord
+  validates :name, length: { maximum: 512 }
+  validates :email, length: { maximum: 512 }
+  validates :name, presence: true, unless: :email
+  validates :email, presence: true, unless: :name
+
+  # Prepares a value to be inserted into a column in the table
+  # `merge_request_diff_commit_users`. Values in this table are limited to
+  # 512 characters.
+  #
+  # We treat empty strings as NULL values, as there's no point in (for
+  # example) storing a row where both the name and Email are an empty
+  # string. In addition, if we treated them differently we could end up with
+  # two rows: one where field X is NULL, and one where field X is an empty
+  # string. This is redundant, so we avoid storing such data.
+  def self.prepare(value)
+    value.present? ? value[0..511] : nil
+  end
+
+  # Creates a new row, or returns an existing one if a row already exists.
+  def self.find_or_create(name, email)
+    find_or_create_by!(name: name, email: email)
+  rescue ActiveRecord::RecordNotUnique
+    retry
+  end
+
+  # Finds many (name, email) pairs in bulk.
+  def self.bulk_find(pairs)
+    queries = {}
+    rows = []
+
+    pairs.each do |(name, email)|
+      queries[[name, email]] = where(name: name, email: email).to_sql
+    end
+
+    # We may end up having to query many users. To ensure we don't hit any
+    # query size limits, we get a fixed number of users at a time.
+    queries.values.each_slice(1_000).map do |slice|
+      rows.concat(from("(#{slice.join("\nUNION ALL\n")}) #{table_name}").to_a)
+    end
+
+    rows
+  end
+
+  # Finds or creates rows for the given pairs of names and Emails.
+  #
+  # The `names_and_emails` argument must be an Array/Set of tuples like so:
+  #
+  #     [
+  #       [name, email],
+  #       [name, email],
+  #       ...
+  #     ]
+  #
+  # This method expects that the names and Emails have already been trimmed to
+  # at most 512 characters.
+  #
+  # The return value is a Hash that maps these tuples to instances of this
+  # model.
+  def self.bulk_find_or_create(pairs)
+    mapping = {}
+    create = []
+
+    # Over time, fewer new rows need to be created. We take advantage of that
+    # here by first finding all rows that already exist, using a limited number
+    # of queries (in most cases only one query will be needed).
+    bulk_find(pairs).each do |row|
+      mapping[[row.name, row.email]] = row
+    end
+
+    pairs.each do |(name, email)|
+      create << { name: name, email: email } unless mapping[[name, email]]
+    end
+
+    return mapping if create.empty?
+
+    # Sometimes we may need to insert new users into the table. We do this in
+    # bulk, so we only need one INSERT for all missing users.
+    insert_all(create, returning: %w[id name email]).each do |row|
+      mapping[[row['name'], row['email']]] =
+        new(id: row['id'], name: row['name'], email: row['email'])
+    end
+
+    # It's possible for (name, email) pairs to be inserted concurrently,
+    # resulting in the above insert not returning anything. Here we get any
+    # remaining users that were created concurrently.
+    bulk_find(pairs.reject { |pair| mapping.key?(pair) }).each do |row|
+      mapping[[row.name, row.email]] = row
+    end
+
+    mapping
+  end
+end

app/models/merge_request_diff.rb

@@ -701,7 +701,7 @@ class MergeRequestDiff < ApplicationRecord
   end
 
   def load_commits(limit: nil)
-    commits = merge_request_diff_commits.limit(limit)
+    commits = merge_request_diff_commits.with_users.limit(limit)
       .map { |commit| Commit.from_hash(commit.to_hash, project) }
 
     CommitCollection

app/models/merge_request_diff_commit.rb

@@ -9,21 +9,51 @@ class MergeRequestDiffCommit < ApplicationRecord
 
   belongs_to :merge_request_diff
 
+  # This relation is called `commit_author` and not `author`, as the project
+  # import/export logic treats relations named `author` as instances of the
+  # `User` class.
+  #
+  # NOTE: these columns are _not_ indexed, nor do they use foreign keys.
+  #
+  # This is deliberate, as creating these indexes on GitLab.com takes a _very_
+  # long time. In addition, there's no real need for them either based on how
+  # this data is used.
+  #
+  # For more information, refer to the following:
+  #
+  # - https://gitlab.com/gitlab-com/gl-infra/production/-/issues/5038#note_614592881
+  # - https://gitlab.com/gitlab-org/gitlab/-/merge_requests/63669
+  belongs_to :commit_author, class_name: 'MergeRequest::DiffCommitUser'
+  belongs_to :committer, class_name: 'MergeRequest::DiffCommitUser'
+
   sha_attribute :sha
   alias_attribute :id, :sha
 
   serialize :trailers, Serializers::Json # rubocop:disable Cop/ActiveRecordSerialize
   validates :trailers, json_schema: { filename: 'git_trailers' }
 
+  scope :with_users, -> { preload(:commit_author, :committer) }
+
+  # A list of keys of which their values need to be trimmed before they can be
+  # inserted into the merge_request_diff_commit_users table.
+  TRIM_USER_KEYS =
+    %i[author_name author_email committer_name committer_email].freeze
+
   # Deprecated; use `bulk_insert!` from `BulkInsertSafe` mixin instead.
   # cf. https://gitlab.com/gitlab-org/gitlab/issues/207989 for progress
   def self.create_bulk(merge_request_diff_id, commits)
-    rows = commits.map.with_index do |commit, index|
-      # See #parent_ids.
-      commit_hash = commit.to_hash.except(:parent_ids)
+    commit_hashes, user_tuples = prepare_commits_for_bulk_insert(commits)
+    users = MergeRequest::DiffCommitUser.bulk_find_or_create(user_tuples)
+
+    rows = commit_hashes.map.with_index do |commit_hash, index|
       sha = commit_hash.delete(:id)
+      author = users[[commit_hash[:author_name], commit_hash[:author_email]]]
+      committer =
+        users[[commit_hash[:committer_name], commit_hash[:committer_email]]]
 
       commit_hash.merge(
+        commit_author_id: author&.id,
+        committer_id: committer&.id,
         merge_request_diff_id: merge_request_diff_id,
         relative_order: index,
         sha: Gitlab::Database::ShaAttribute.serialize(sha), # rubocop:disable Cop/ActiveRecordSerialize
@@ -36,6 +66,24 @@ class MergeRequestDiffCommit < ApplicationRecord
     Gitlab::Database.bulk_insert(self.table_name, rows) # rubocop:disable Gitlab/BulkInsert
   end
 
+  def self.prepare_commits_for_bulk_insert(commits)
+    user_tuples = Set.new
+    hashes = commits.map do |commit|
+      hash = commit.to_hash.except(:parent_ids)
+
+      TRIM_USER_KEYS.each do |key|
+        hash[key] = MergeRequest::DiffCommitUser.prepare(hash[key])
+      end
+
+      user_tuples << [hash[:author_name], hash[:author_email]]
+      user_tuples << [hash[:committer_name], hash[:committer_email]]
+
+      hash
+    end
+
+    [hashes, user_tuples]
+  end
+
   def self.oldest_merge_request_id_per_commit(project_id, shas)
     # This method is defined here and not on MergeRequest, otherwise the SHA
     # values used in the WHERE below won't be encoded correctly.
@@ -54,4 +102,20 @@ class MergeRequestDiffCommit < ApplicationRecord
       )
       .group(:sha)
   end
+
+  def author_name
+    commit_author_id ? commit_author.name : super
+  end
+
+  def author_email
+    commit_author_id ? commit_author.email : super
+  end
+
+  def committer_name
+    committer_id ? committer.name : super
+  end
+
+  def committer_email
+    committer_id ? committer.email : super
+  end
 end

db/migrate/20210602155056_add_merge_request_diff_commit_users.rb

+# frozen_string_literal: true
+
+class AddMergeRequestDiffCommitUsers < ActiveRecord::Migration[6.1]
+  include Gitlab::Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  def up
+    create_table_with_constraints :merge_request_diff_commit_users, id: :bigint do |t|
+      t.text :name
+      t.text :email
+
+      t.text_limit :name, 512
+      t.text_limit :email, 512
+
+      t.index [:name, :email], unique: true
+    end
+
+    # Names or Emails can be optional, so in some cases one of these may be
+    # null. But if both are NULL/empty, no row should exist in this table.
+    add_check_constraint(
+      :merge_request_diff_commit_users,
+      "(COALESCE(name, '') != '') OR (COALESCE(email, '') != '')",
+      :merge_request_diff_commit_users_name_or_email_existence
+    )
+  end
+
+  def down
+    drop_table :merge_request_diff_commit_users
+  end
+end

db/migrate/20210602155110_add_merge_request_diff_commit_user_columns.rb

+# frozen_string_literal: true
+
+class AddMergeRequestDiffCommitUserColumns < ActiveRecord::Migration[6.1]
+  include Gitlab::Database::MigrationHelpers
+
+  def up
+    # NOTE: these columns are _not_ indexed, nor do they use foreign keys.
+    #
+    # This is deliberate, as creating these indexes on GitLab.com takes a _very_
+    # long time. In addition, there's no real need for them either based on how
+    # this data is used.
+    #
+    # For more information, refer to the following:
+    #
+    # - https://gitlab.com/gitlab-com/gl-infra/production/-/issues/5038#note_614592881
+    # - https://gitlab.com/gitlab-org/gitlab/-/merge_requests/63669
+    add_column(:merge_request_diff_commits, :commit_author_id, :bigint)
+    add_column(:merge_request_diff_commits, :committer_id, :bigint)
+  end
+
+  def down
+    remove_column(:merge_request_diff_commits, :commit_author_id)
+    remove_column(:merge_request_diff_commits, :committer_id)
+  end
+end

db/post_migrate/20210604133651_schedule_merge_request_diff_users_background_migration.rb

+# frozen_string_literal: true
+
+class ScheduleMergeRequestDiffUsersBackgroundMigration < ActiveRecord::Migration[6.1]
+  include Gitlab::Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  # The number of rows to process in a single migration job.
+  #
+  # The minimum interval for background migrations is two minutes. On staging we
+  # observed we can process roughly 20 000 rows in a minute. Based on the total
+  # number of rows on staging, this translates to a total processing time of
+  # roughly 14 days.
+  #
+  # By using a batch size of 40 000, we maintain a rate of roughly 20 000 rows
+  # per minute, hopefully keeping the total migration time under two weeks;
+  # instead of four weeks.
+  BATCH_SIZE = 40_000
+
+  MIGRATION_NAME = 'MigrateMergeRequestDiffCommitUsers'
+
+  class MergeRequestDiff < ActiveRecord::Base
+    self.table_name = 'merge_request_diffs'
+  end
+
+  def up
+    start = MergeRequestDiff.minimum(:id).to_i
+    max = MergeRequestDiff.maximum(:id).to_i
+    delay = BackgroundMigrationWorker.minimum_interval
+
+    # The table merge_request_diff_commits contains _a lot_ of rows (roughly 400
+    # 000 000 on staging). Iterating a table that large to determine job ranges
+    # would take a while.
+    #
+    # To avoid that overhead, we simply schedule fixed ranges according to the
+    # minimum and maximum IDs. The background migration in turn only processes
+    # rows that actually exist.
+    while start < max
+      stop = start + BATCH_SIZE
+
+      migrate_in(delay, MIGRATION_NAME, [start, stop])
+
+      Gitlab::Database::BackgroundMigrationJob
+        .create!(class_name: MIGRATION_NAME, arguments: [start, stop])
+
+      delay += BackgroundMigrationWorker.minimum_interval
+      start += BATCH_SIZE
+    end
+  end
+
+  def down
+    # no-op
+  end
+end

db/schema_migrations/20210602155056

+42b3090efee66f5a7a5c06d8768d1417892c5d6745f60163a09f58e6e3722761
\ No newline at end of file

db/schema_migrations/20210602155110

+aa04d433e400ed3ec11e5d40ada72f122b1d8b7a82f8803d9206da5c94ec5ef9
\ No newline at end of file

db/schema_migrations/20210604133651

+0c01bb41113c468a602649b591e1fd2959a6e3190c835ef2e27351cf69f50fd5
\ No newline at end of file

db/structure.sql

@@ -14760,6 +14760,24 @@ CREATE SEQUENCE merge_request_context_commits_id_seq
 
 ALTER SEQUENCE merge_request_context_commits_id_seq OWNED BY merge_request_context_commits.id;
 
+CREATE TABLE merge_request_diff_commit_users (
+    id bigint NOT NULL,
+    name text,
+    email text,
+    CONSTRAINT check_147358fc42 CHECK ((char_length(name) <= 512)),
+    CONSTRAINT check_f5fa206cf7 CHECK ((char_length(email) <= 512)),
+    CONSTRAINT merge_request_diff_commit_users_name_or_email_existence CHECK (((COALESCE(name, ''::text) <> ''::text) OR (COALESCE(email, ''::text) <> ''::text)))
+);
+
+CREATE SEQUENCE merge_request_diff_commit_users_id_seq
+    START WITH 1
+    INCREMENT BY 1
+    NO MINVALUE
+    NO MAXVALUE
+    CACHE 1;
+
+ALTER SEQUENCE merge_request_diff_commit_users_id_seq OWNED BY merge_request_diff_commit_users.id;
+
 CREATE TABLE merge_request_diff_commits (
     authored_date timestamp without time zone,
     committed_date timestamp without time zone,
@@ -14771,7 +14789,9 @@ CREATE TABLE merge_request_diff_commits (
     committer_name text,
     committer_email text,
     message text,
-    trailers jsonb DEFAULT '{}'::jsonb NOT NULL
+    trailers jsonb DEFAULT '{}'::jsonb NOT NULL,
+    commit_author_id bigint,
+    committer_id bigint
 );
 
 CREATE TABLE merge_request_diff_details (
@@ -20161,6 +20181,8 @@ ALTER TABLE ONLY merge_request_cleanup_schedules ALTER COLUMN merge_request_id S
 
 ALTER TABLE ONLY merge_request_context_commits ALTER COLUMN id SET DEFAULT nextval('merge_request_context_commits_id_seq'::regclass);
 
+ALTER TABLE ONLY merge_request_diff_commit_users ALTER COLUMN id SET DEFAULT nextval('merge_request_diff_commit_users_id_seq'::regclass);
+
 ALTER TABLE ONLY merge_request_diff_details ALTER COLUMN merge_request_diff_id SET DEFAULT nextval('merge_request_diff_details_merge_request_diff_id_seq'::regclass);
 
 ALTER TABLE ONLY merge_request_diffs ALTER COLUMN id SET DEFAULT nextval('merge_request_diffs_id_seq'::regclass);
@@ -21601,6 +21623,9 @@ ALTER TABLE ONLY merge_request_context_commit_diff_files
 ALTER TABLE ONLY merge_request_context_commits
     ADD CONSTRAINT merge_request_context_commits_pkey PRIMARY KEY (id);
 
+ALTER TABLE ONLY merge_request_diff_commit_users
+    ADD CONSTRAINT merge_request_diff_commit_users_pkey PRIMARY KEY (id);
+
 ALTER TABLE ONLY merge_request_diff_commits
     ADD CONSTRAINT merge_request_diff_commits_pkey PRIMARY KEY (merge_request_diff_id, relative_order);
 
@@ -23904,6 +23929,8 @@ CREATE INDEX index_merge_request_blocks_on_blocked_merge_request_id ON merge_req
 
 CREATE UNIQUE INDEX index_merge_request_cleanup_schedules_on_merge_request_id ON merge_request_cleanup_schedules USING btree (merge_request_id);
 
+CREATE UNIQUE INDEX index_merge_request_diff_commit_users_on_name_and_email ON merge_request_diff_commit_users USING btree (name, email);
+
 CREATE INDEX index_merge_request_diff_commits_on_sha ON merge_request_diff_commits USING btree (sha);
 
 CREATE INDEX index_merge_request_diff_details_failed_verification ON merge_request_diff_details USING btree (verification_retry_at NULLS FIRST) WHERE (verification_state = 3);

lib/gitlab/background_migration/migrate_merge_request_diff_commit_users.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module BackgroundMigration
+    # Migrates author and committer names and emails from
+    # merge_request_diff_commits to two columns that point to
+    # merge_request_diff_commit_users.
+    #
+    # rubocop: disable Metrics/ClassLength
+    class MigrateMergeRequestDiffCommitUsers
+      # The number of user rows in merge_request_diff_commit_users to get in a
+      # single query.
+      USER_ROWS_PER_QUERY = 1_000
+
+      # The number of rows in merge_request_diff_commits to get in a single
+      # query.
+      COMMIT_ROWS_PER_QUERY = 10_000
+
+      # The number of rows in merge_request_diff_commits to update in a single
+      # query.
+      #
+      # Tests in staging revealed that increasing the number of updates per
+      # query translates to a longer total runtime for a migration. For example,
+      # given the same range of rows to migrate, 1000 updates per query required
+      # a total of roughly 15 seconds. On the other hand, 5000 updates per query
+      # required a total of roughly 25 seconds. For this reason, we use a value
+      # of 1000 rows per update.
+      UPDATES_PER_QUERY = 1_000
+
+      # rubocop: disable Style/Documentation
+      class MergeRequestDiffCommit < ActiveRecord::Base
+        include FromUnion
+        extend ::SuppressCompositePrimaryKeyWarning
+
+        self.table_name = 'merge_request_diff_commits'
+
+        # Yields each row to migrate in the given range.
+        #
+        # This method uses keyset pagination to ensure we don't retrieve
+        # potentially tens of thousands (or even hundreds of thousands) of rows
+        # in a single query. Such queries could time out, or increase the amount
+        # of memory needed to process the data.
+        #
+        # We can't use `EachBatch` and similar approaches, as
+        # merge_request_diff_commits doesn't have a single monotonically
+        # increasing primary key.
+        def self.each_row_to_migrate(start_id, stop_id, &block)
+          order = Pagination::Keyset::Order.build(
+            %w[merge_request_diff_id relative_order].map do |col|
+              Pagination::Keyset::ColumnOrderDefinition.new(
+                attribute_name: col,
+                order_expression: self.arel_table[col.to_sym].asc,
+                nullable: :not_nullable,
+                distinct: false
+              )
+            end
+          )
+
+          scope = MergeRequestDiffCommit
+            .where(merge_request_diff_id: start_id...stop_id)
+            .order(order)
+
+          Pagination::Keyset::Iterator
+            .new(scope: scope, use_union_optimization: true)
+            .each_batch(of: COMMIT_ROWS_PER_QUERY) { |rows| rows.each(&block) }
+        end
+      end
+      # rubocop: enable Style/Documentation
+
+      # rubocop: disable Style/Documentation
+      class MergeRequestDiffCommitUser < ActiveRecord::Base
+        self.table_name = 'merge_request_diff_commit_users'
+
+        def self.union(queries)
+          from("(#{queries.join("\nUNION ALL\n")}) #{table_name}")
+        end
+      end
+      # rubocop: enable Style/Documentation
+
+      def perform(start_id, stop_id)
+        # This Hash maps user names + emails to their corresponding rows in
+        # merge_request_diff_commit_users.
+        user_mapping = {}
+
+        user_details, diff_rows_to_update = get_data_to_update(start_id, stop_id)
+
+        get_user_rows_in_batches(user_details, user_mapping)
+        create_missing_users(user_details, user_mapping)
+        update_commit_rows(diff_rows_to_update, user_mapping)
+
+        Database::BackgroundMigrationJob.mark_all_as_succeeded(
+          'MigrateMergeRequestDiffCommitUsers',
+          [start_id, stop_id]
+        )
+      end
+
+      # Returns the data we'll use to determine what merge_request_diff_commits
+      # rows to update, and what data to use for populating their
+      # commit_author_id and committer_id columns.
+      def get_data_to_update(start_id, stop_id)
+        # This Set is used to retrieve users that already exist in
+        # merge_request_diff_commit_users.
+        users = Set.new
+
+        # This Hash maps the primary key of every row in
+        # merge_request_diff_commits to the (trimmed) author and committer
+        # details to use for updating the row.
+        to_update = {}
+
+        MergeRequestDiffCommit.each_row_to_migrate(start_id, stop_id) do |row|
+          author = [prepare(row.author_name), prepare(row.author_email)]
+          committer = [prepare(row.committer_name), prepare(row.committer_email)]
+
+          to_update[[row.merge_request_diff_id, row.relative_order]] =
+            [author, committer]
+
+          users << author if author[0] || author[1]
+          users << committer if committer[0] || committer[1]
+        end
+
+        [users, to_update]
+      end
+
+      # Gets any existing rows in merge_request_diff_commit_users in batches.
+      #
+      # This method may end up having to retrieve lots of rows. To reduce the
+      # overhead, we batch queries into a UNION query. We limit the number of
+      # queries per UNION so we don't end up sending a single query containing
+      # too many SELECT statements.
+      def get_user_rows_in_batches(users, user_mapping)
+        users.each_slice(USER_ROWS_PER_QUERY) do |pairs|
+          queries = pairs.map do |(name, email)|
+            MergeRequestDiffCommitUser.where(name: name, email: email).to_sql
+          end
+
+          MergeRequestDiffCommitUser.union(queries).each do |row|
+            user_mapping[[row.name.to_s, row.email.to_s]] = row
+          end
+        end
+      end
+
+      # Creates any users for which no row exists in
+      # merge_request_diff_commit_users.
+      #
+      # Not all users queried may exist yet, so we need to create any missing
+      # ones; making sure we handle concurrent creations of the same user
+      def create_missing_users(users, mapping)
+        create = []
+
+        users.each do |(name, email)|
+          create << { name: name, email: email } unless mapping[[name, email]]
+        end
+
+        return if create.empty?
+
+        MergeRequestDiffCommitUser
+          .insert_all(create, returning: %w[id name email])
+          .each do |row|
+            mapping[[row['name'], row['email']]] = MergeRequestDiffCommitUser
+              .new(id: row['id'], name: row['name'], email: row['email'])
+          end
+
+        # It's possible for (name, email) pairs to be inserted concurrently,
+        # resulting in the above insert not returning anything. Here we get any
+        # remaining users that were created concurrently.
+        get_user_rows_in_batches(
+          users.reject { |pair| mapping.key?(pair) },
+          mapping
+        )
+      end
+
+      # Updates rows in merge_request_diff_commits with their new
+      # commit_author_id and committer_id values.
+      def update_commit_rows(to_update, user_mapping)
+        MergeRequestDiffCommitUser.transaction do
+          to_update.each_slice(UPDATES_PER_QUERY) do |slice|
+            updates = {}
+
+            slice.each do |(diff_id, order), (author, committer)|
+              author_id = user_mapping[author]&.id
+              committer_id = user_mapping[committer]&.id
+
+              updates[[diff_id, order]] = [author_id, committer_id]
+            end
+
+            bulk_update_commit_rows(updates)
+          end
+        end
+      end
+
+      # Bulk updates rows in the merge_request_diff_commits table with their new
+      # author and/or committer ID values.
+      #
+      # Updates are batched together to reduce the overhead of having to produce
+      # a single UPDATE for every row, as we may end up having to update
+      # thousands of rows at once.
+      #
+      # The query produced by this method is along the lines of the following:
+      #
+      #     UPDATE merge_request_diff_commits
+      #     SET commit_author_id =
+      #       CASE
+      #       WHEN (merge_request_diff_id, relative_order) = (x, y) THEN X
+      #       WHEN ...
+      #       END,
+      #     committer_id =
+      #       CASE
+      #       WHEN (merge_request_diff_id, relative_order) = (x, y) THEN Y
+      #       WHEN ...
+      #       END
+      #     WHERE (merge_request_diff_id, relative_order) IN ( (x, y), ... )
+      #
+      # The `mapping` argument is a Hash in the following format:
+      #
+      #     { [merge_request_diff_id, relative_order] => [author_id, committer_id] }
+      #
+      # rubocop: disable Metrics/AbcSize
+      def bulk_update_commit_rows(mapping)
+        author_case = Arel::Nodes::Case.new
+        committer_case = Arel::Nodes::Case.new
+        primary_values = []
+
+        mapping.each do |diff_id_and_order, (author_id, committer_id)|
+          primary_value = Arel::Nodes::Grouping.new(diff_id_and_order)
+
+          primary_values << primary_value
+
+          if author_id
+            author_case.when(primary_key.eq(primary_value)).then(author_id)
+          end
+
+          if committer_id
+            committer_case.when(primary_key.eq(primary_value)).then(committer_id)
+          end
+        end
+
+        if author_case.conditions.empty? && committer_case.conditions.empty?
+          return
+        end
+
+        fields = []
+
+        # Statements such as `SET x = CASE END` are not valid SQL statements, so
+        # we omit setting an ID field if there are no values to populate it
+        # with.
+        if author_case.conditions.any?
+          fields << [arel_table[:commit_author_id], author_case]
+        end
+
+        if committer_case.conditions.any?
+          fields << [arel_table[:committer_id], committer_case]
+        end
+
+        query = Arel::UpdateManager.new
+          .table(arel_table)
+          .where(primary_key.in(primary_values))
+          .set(fields)
+          .to_sql
+
+        MergeRequestDiffCommit.connection.execute(query)
+      end
+      # rubocop: enable Metrics/AbcSize
+
+      def primary_key
+        Arel::Nodes::Grouping.new(
+          [arel_table[:merge_request_diff_id], arel_table[:relative_order]]
+        )
+      end
+
+      def arel_table
+        MergeRequestDiffCommit.arel_table
+      end
+
+      # Prepares a value to be inserted into a column in the table
+      # `merge_request_diff_commit_users`. Values in this table are limited to
+      # 512 characters.
+      #
+      # We treat empty strings as NULL values, as there's no point in (for
+      # example) storing a row where both the name and Email are an empty
+      # string. In addition, if we treated them differently we could end up with
+      # two rows: one where field X is NULL, and one where field X is an empty
+      # string. This is redundant, so we avoid storing such data.
+      def prepare(value)
+        value.present? ? value[0..511] : nil
+      end
+    end
+    # rubocop: enable Metrics/ClassLength
+  end
+end

lib/gitlab/import_export/project/import_export.yml

@@ -61,7 +61,9 @@ tree:
           - :push_event_payload
         - :suggestions
       - merge_request_diff:
-        - :merge_request_diff_commits
+        - merge_request_diff_commits:
+          - :commit_author
+          - :committer
         - :merge_request_diff_files
       - events:
         - :push_event_payload
@@ -201,6 +203,10 @@ excluded_attributes:
     - :verification_failure
   merge_request_diff_commits:
     - :merge_request_diff_id
+    - :commit_author_id
+    - :committer_id
+  merge_request_diff_commit_user:
+    - :id
   merge_request_diff_detail:
     - :merge_request_diff_id
     - :verification_retry_at

lib/gitlab/import_export/project/object_builder.rb

@@ -28,6 +28,7 @@ module Gitlab
 
         def find
           return if epic? && group.nil?
+          return find_diff_commit_user if diff_commit_user?
 
           super
         end
@@ -81,6 +82,13 @@ module Gitlab
           end
         end
 
+        def find_diff_commit_user
+          find_with_cache do
+            MergeRequest::DiffCommitUser
+              .find_or_create(@attributes['name'], @attributes['email'])
+          end
+        end
+
         def label?
           klass == Label
         end
@@ -101,6 +109,10 @@ module Gitlab
           klass == DesignManagement::Design
         end
 
+        def diff_commit_user?
+          klass == MergeRequest::DiffCommitUser
+        end
+
         # If an existing group milestone used the IID
         # claim the IID back and set the group milestone to use one available
         # This is necessary to fix situations like the following:

lib/gitlab/import_export/project/relation_factory.rb

@@ -31,7 +31,9 @@ module Gitlab
                       ci_cd_settings: 'ProjectCiCdSetting',
                       error_tracking_setting: 'ErrorTracking::ProjectErrorTrackingSetting',
                       links: 'Releases::Link',
-                      metrics_setting: 'ProjectMetricsSetting' }.freeze
+                      metrics_setting: 'ProjectMetricsSetting',
+                      commit_author: 'MergeRequest::DiffCommitUser',
+                      committer: 'MergeRequest::DiffCommitUser' }.freeze
 
         BUILD_MODELS = %i[Ci::Build commit_status].freeze
 
@@ -56,6 +58,7 @@ module Gitlab
           external_pull_request
           external_pull_requests
           DesignManagement::Design
+          MergeRequest::DiffCommitUser
         ].freeze
 
         def create

spec/db/schema_spec.rb

@@ -56,6 +56,7 @@ RSpec.describe 'Database schema' do
     ldap_group_links: %w[group_id],
     members: %w[source_id created_by_id],
     merge_requests: %w[last_edited_by_id state_id],
+    merge_request_diff_commits: %w[commit_author_id committer_id],
     namespaces: %w[owner_id parent_id],
     notes: %w[author_id commit_id noteable_id updated_by_id resolved_by_id confirmed_by_id discussion_id],
     notification_settings: %w[source_id],

spec/factories/merge_request_diff_commit_users.rb

+# frozen_string_literal: true
+
+FactoryBot.define do
+  factory :merge_request_diff_commit_user, class: 'MergeRequest::DiffCommitUser' do
+    name { generate(:name) }
+    email { generate(:email) }
+  end
+end

spec/fixtures/lib/gitlab/import_export/complex/project.json

@@ -2799,7 +2799,15 @@
             "author_email": "dmitriy.zaporozhets@gmail.com",
             "committed_date": "2014-08-06T08:35:52.000+02:00",
             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 27,
@@ -2811,7 +2819,15 @@
             "author_email": "dmitriy.zaporozhets@gmail.com",
             "committed_date": "2014-02-27T10:01:38.000+01:00",
             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 27,
@@ -2823,7 +2839,15 @@
             "author_email": "dmitriy.zaporozhets@gmail.com",
             "committed_date": "2014-02-27T09:57:31.000+01:00",
             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 27,
@@ -2835,7 +2859,15 @@
             "author_email": "dmitriy.zaporozhets@gmail.com",
             "committed_date": "2014-02-27T09:54:21.000+01:00",
             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 27,
@@ -2847,7 +2879,15 @@
             "author_email": "dmitriy.zaporozhets@gmail.com",
             "committed_date": "2014-02-27T09:49:50.000+01:00",
             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 27,
@@ -2859,7 +2899,15 @@
             "author_email": "dmitriy.zaporozhets@gmail.com",
             "committed_date": "2014-02-27T09:48:32.000+01:00",
             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
           }
         ],
         "merge_request_diff_files": [
@@ -3247,7 +3295,15 @@
             "author_email": "dmitriy.zaporozhets@gmail.com",
             "committed_date": "2014-02-27T09:26:01.000+01:00",
             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
           }
         ],
         "merge_request_diff_files": [
@@ -3510,7 +3566,15 @@
             "author_email": "james@jameslopez.es",
             "committed_date": "2016-01-19T13:22:56.000+01:00",
             "committer_name": "James Lopez",
-            "committer_email": "james@jameslopez.es"
+            "committer_email": "james@jameslopez.es",
+            "commit_author": {
+              "name": "James Lopez",
+              "email": "james@jameslopez.es"
+            },
+            "committer": {
+              "name": "James Lopez",
+              "email": "james@jameslopez.es"
+            }
           }
         ],
         "merge_request_diff_files": [
@@ -3773,7 +3837,15 @@
             "author_email": "james@jameslopez.es",
             "committed_date": "2016-01-19T14:14:43.000+01:00",
             "committer_name": "James Lopez",
-            "committer_email": "james@jameslopez.es"
+            "committer_email": "james@jameslopez.es",
+            "commit_author": {
+              "name": "James Lopez",
+              "email": "james@jameslopez.es"
+            },
+            "committer": {
+              "name": "James Lopez",
+              "email": "james@jameslopez.es"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3785,7 +3857,15 @@
             "author_email": "marin@gitlab.com",
             "committed_date": "2015-12-07T12:52:12.000+01:00",
             "committer_name": "Marin Jankovski",
-            "committer_email": "marin@gitlab.com"
+            "committer_email": "marin@gitlab.com",
+            "commit_author": {
+              "name": "Marin Jankovski",
+              "email": "marin@gitlab.com"
+            },
+            "committer": {
+              "name": "Marin Jankovski",
+              "email": "marin@gitlab.com"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3797,7 +3877,15 @@
             "author_email": "maxlazio@gmail.com",
             "committed_date": "2015-12-07T11:54:28.000+01:00",
             "committer_name": "Marin Jankovski",
-            "committer_email": "maxlazio@gmail.com"
+            "committer_email": "maxlazio@gmail.com",
+            "commit_author": {
+              "name": "Marin Jankovski",
+              "email": "maxlazio@gmail.com"
+            },
+            "committer": {
+              "name": "Marin Jankovski",
+              "email": "maxlazio@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3809,7 +3897,15 @@
             "author_email": "stanhu@gmail.com",
             "committed_date": "2015-11-13T16:27:12.000+01:00",
             "committer_name": "Stan Hu",
-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3821,7 +3917,15 @@
             "author_email": "stanhu@gmail.com",
             "committed_date": "2015-11-13T08:50:17.000+01:00",
             "committer_name": "Stan Hu",
-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3833,7 +3937,15 @@
             "author_email": "stanhu@gmail.com",
             "committed_date": "2015-11-13T08:39:43.000+01:00",
             "committer_name": "Stan Hu",
-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3845,7 +3957,15 @@
             "author_email": "stanhu@gmail.com",
             "committed_date": "2015-11-13T07:21:40.000+01:00",
             "committer_name": "Stan Hu",
-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3857,7 +3977,15 @@
             "author_email": "minsik.yoon@samsung.com",
             "committed_date": "2015-11-13T06:01:27.000+01:00",
             "committer_name": "윤민식",
-            "committer_email": "minsik.yoon@samsung.com"
+            "committer_email": "minsik.yoon@samsung.com",
+            "commit_author": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            },
+            "committer": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3869,7 +3997,15 @@
             "author_email": "minsik.yoon@samsung.com",
             "committed_date": "2015-11-13T06:00:16.000+01:00",
             "committer_name": "윤민식",
-            "committer_email": "minsik.yoon@samsung.com"
+            "committer_email": "minsik.yoon@samsung.com",
+            "commit_author": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            },
+            "committer": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3881,7 +4017,15 @@
             "author_email": "stanhu@gmail.com",
             "committed_date": "2015-11-13T05:23:14.000+01:00",
             "committer_name": "Stan Hu",
-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3893,7 +4037,15 @@
             "author_email": "minsik.yoon@samsung.com",
             "committed_date": "2015-11-13T05:08:45.000+01:00",
             "committer_name": "윤민식",
-            "committer_email": "minsik.yoon@samsung.com"
+            "committer_email": "minsik.yoon@samsung.com",
+            "commit_author": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            },
+            "committer": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3905,7 +4057,15 @@
             "author_email": "minsik.yoon@samsung.com",
             "committed_date": "2015-11-13T05:08:04.000+01:00",
             "committer_name": "윤민식",
-            "committer_email": "minsik.yoon@samsung.com"
+            "committer_email": "minsik.yoon@samsung.com",
+            "commit_author": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            },
+            "committer": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3917,7 +4077,15 @@
             "author_email": "stanhu@packetzoom.com",
             "committed_date": "2015-08-25T17:53:12.000+02:00",
             "committer_name": "Stan Hu",
-            "committer_email": "stanhu@packetzoom.com"
+            "committer_email": "stanhu@packetzoom.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@packetzoom.com"
+            },
+            "committer": {
+              "name": "Stan Hu",
+              "email": "stanhu@packetzoom.com"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3929,7 +4097,15 @@
             "author_email": "sytse@gitlab.com",
             "committed_date": "2015-01-10T22:23:29.000+01:00",
             "committer_name": "Sytse Sijbrandij",
-            "committer_email": "sytse@gitlab.com"
+            "committer_email": "sytse@gitlab.com",
+            "commit_author": {
+              "name": "Sytse Sijbrandij",
+              "email": "sytse@gitlab.com"
+            },
+            "committer": {
+              "name": "Sytse Sijbrandij",
+              "email": "sytse@gitlab.com"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3941,7 +4117,15 @@
             "author_email": "marmis85@gmail.com",
             "committed_date": "2015-01-10T21:28:18.000+01:00",
             "committer_name": "marmis85",
-            "committer_email": "marmis85@gmail.com"
+            "committer_email": "marmis85@gmail.com",
+            "commit_author": {
+              "name": "marmis85",
+              "email": "marmis85@gmail.com"
+            },
+            "committer": {
+              "name": "marmis85",
+              "email": "marmis85@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3953,7 +4137,15 @@
             "author_email": "dmitriy.zaporozhets@gmail.com",
             "committed_date": "2014-02-27T10:01:38.000+01:00",
             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 14,
@@ -3965,7 +4157,15 @@
             "author_email": "dmitriy.zaporozhets@gmail.com",
             "committed_date": "2014-02-27T09:57:31.000+01:00",
             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
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+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
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+              "email": "dmitriy.zaporozhets@gmail.com"
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@@ -3977,7 +4177,15 @@
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-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
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+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
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@@ -3989,7 +4197,15 @@
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             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
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@@ -4001,7 +4217,15 @@
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             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
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@@ -4458,7 +4682,15 @@
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             "committer_name": "James Lopez",
-            "committer_email": "james@jameslopez.es"
+            "committer_email": "james@jameslopez.es",
+            "commit_author": {
+              "name": "James Lopez",
+              "email": "james@jameslopez.es"
+            },
+            "committer": {
+              "name": "James Lopez",
+              "email": "james@jameslopez.es"
+            }
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@@ -4470,7 +4702,15 @@
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             "committer_name": "Marin Jankovski",
-            "committer_email": "marin@gitlab.com"
+            "committer_email": "marin@gitlab.com",
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+              "email": "marin@gitlab.com"
+            },
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+              "name": "Marin Jankovski",
+              "email": "marin@gitlab.com"
+            }
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@@ -4482,7 +4722,15 @@
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             "committer_name": "Marin Jankovski",
-            "committer_email": "maxlazio@gmail.com"
+            "committer_email": "maxlazio@gmail.com",
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+              "name": "Marin Jankovski",
+              "email": "maxlazio@gmail.com"
+            },
+            "committer": {
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+              "email": "maxlazio@gmail.com"
+            }
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@@ -4494,7 +4742,15 @@
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             "committer_name": "Stan Hu",
-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
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+              "email": "stanhu@gmail.com"
+            }
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@@ -4506,7 +4762,15 @@
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             "committer_name": "Stan Hu",
-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
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+              "email": "stanhu@gmail.com"
+            }
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@@ -4518,7 +4782,15 @@
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+            "committer_email": "stanhu@gmail.com",
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+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
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+              "email": "stanhu@gmail.com"
+            }
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@@ -4530,7 +4802,15 @@
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+            "committer_email": "stanhu@gmail.com",
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+              "email": "stanhu@gmail.com"
+            },
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+              "email": "stanhu@gmail.com"
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@@ -4542,7 +4822,15 @@
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+            "committer_email": "minsik.yoon@samsung.com",
+            "commit_author": {
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+              "email": "minsik.yoon@samsung.com"
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+              "email": "minsik.yoon@samsung.com"
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@@ -4554,7 +4842,15 @@
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-            "committer_email": "minsik.yoon@samsung.com"
+            "committer_email": "minsik.yoon@samsung.com",
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+              "email": "minsik.yoon@samsung.com"
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@@ -4566,7 +4862,15 @@
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-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
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+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
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+              "email": "stanhu@gmail.com"
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@@ -4578,7 +4882,15 @@
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+            "committer_email": "minsik.yoon@samsung.com",
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+              "email": "minsik.yoon@samsung.com"
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@@ -4590,7 +4902,15 @@
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-            "committer_email": "minsik.yoon@samsung.com"
+            "committer_email": "minsik.yoon@samsung.com",
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+              "email": "minsik.yoon@samsung.com"
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+              "email": "minsik.yoon@samsung.com"
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@@ -4602,7 +4922,15 @@
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+            "committer_email": "stanhu@packetzoom.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@packetzoom.com"
+            },
+            "committer": {
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+              "email": "stanhu@packetzoom.com"
+            }
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@@ -4614,7 +4942,15 @@
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-            "committer_email": "sytse@gitlab.com"
+            "committer_email": "sytse@gitlab.com",
+            "commit_author": {
+              "name": "Sytse Sijbrandij",
+              "email": "sytse@gitlab.com"
+            },
+            "committer": {
+              "name": "Sytse Sijbrandij",
+              "email": "sytse@gitlab.com"
+            }
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@@ -4626,7 +4962,15 @@
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+            "committer_email": "marmis85@gmail.com",
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+              "email": "marmis85@gmail.com"
+            },
+            "committer": {
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@@ -4967,7 +5311,15 @@
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             "committer_name": "James Lopez",
-            "committer_email": "james@jameslopez.es"
+            "committer_email": "james@jameslopez.es",
+            "commit_author": {
+              "name": "James Lopez",
+              "email": "james@jameslopez.es"
+            },
+            "committer": {
+              "name": "James Lopez",
+              "email": "james@jameslopez.es"
+            }
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@@ -4979,7 +5331,15 @@
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-            "committer_email": "marin@gitlab.com"
+            "committer_email": "marin@gitlab.com",
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+              "name": "Marin Jankovski",
+              "email": "marin@gitlab.com"
+            },
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+              "email": "marin@gitlab.com"
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@@ -4991,7 +5351,15 @@
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-            "committer_email": "maxlazio@gmail.com"
+            "committer_email": "maxlazio@gmail.com",
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+              "email": "maxlazio@gmail.com"
+            },
+            "committer": {
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+              "email": "maxlazio@gmail.com"
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@@ -5003,7 +5371,15 @@
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-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
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+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
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+              "email": "stanhu@gmail.com"
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@@ -5015,7 +5391,15 @@
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-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
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+              "email": "stanhu@gmail.com"
+            }
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@@ -5027,7 +5411,15 @@
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             "committer_name": "Stan Hu",
-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
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+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
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+              "email": "stanhu@gmail.com"
+            }
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@@ -5039,7 +5431,15 @@
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-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
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+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
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+              "email": "stanhu@gmail.com"
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@@ -5051,7 +5451,15 @@
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-            "committer_email": "minsik.yoon@samsung.com"
+            "committer_email": "minsik.yoon@samsung.com",
+            "commit_author": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            },
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+              "email": "minsik.yoon@samsung.com"
+            }
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@@ -5063,7 +5471,15 @@
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-            "committer_email": "minsik.yoon@samsung.com"
+            "committer_email": "minsik.yoon@samsung.com",
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+              "email": "minsik.yoon@samsung.com"
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+              "email": "minsik.yoon@samsung.com"
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@@ -5075,7 +5491,15 @@
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-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
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+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
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+              "email": "stanhu@gmail.com"
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@@ -5087,7 +5511,15 @@
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+            "committer_email": "minsik.yoon@samsung.com",
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+              "email": "minsik.yoon@samsung.com"
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+              "email": "minsik.yoon@samsung.com"
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@@ -5099,7 +5531,15 @@
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-            "committer_email": "minsik.yoon@samsung.com"
+            "committer_email": "minsik.yoon@samsung.com",
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+              "email": "minsik.yoon@samsung.com"
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@@ -5111,7 +5551,15 @@
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+            "committer_email": "stanhu@packetzoom.com",
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+              "email": "stanhu@packetzoom.com"
+            },
+            "committer": {
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+            }
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@@ -5675,7 +6123,15 @@
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+            "committer_email": "james@jameslopez.es",
+            "commit_author": {
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+              "email": "james@jameslopez.es"
+            },
+            "committer": {
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+              "email": "james@jameslopez.es"
+            }
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@@ -5687,7 +6143,15 @@
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+            "committer_email": "marin@gitlab.com",
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+              "email": "marin@gitlab.com"
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+              "email": "marin@gitlab.com"
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@@ -5699,7 +6163,15 @@
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+            "committer_email": "maxlazio@gmail.com",
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+              "email": "maxlazio@gmail.com"
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+              "email": "maxlazio@gmail.com"
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@@ -5711,7 +6183,15 @@
             "author_email": "stanhu@gmail.com",
             "committed_date": "2015-11-13T16:27:12.000+01:00",
             "committer_name": "Stan Hu",
-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5723,7 +6203,15 @@
             "author_email": "stanhu@gmail.com",
             "committed_date": "2015-11-13T08:50:17.000+01:00",
             "committer_name": "Stan Hu",
-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5735,7 +6223,15 @@
             "author_email": "stanhu@gmail.com",
             "committed_date": "2015-11-13T08:39:43.000+01:00",
             "committer_name": "Stan Hu",
-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5747,7 +6243,15 @@
             "author_email": "stanhu@gmail.com",
             "committed_date": "2015-11-13T07:21:40.000+01:00",
             "committer_name": "Stan Hu",
-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5759,7 +6263,15 @@
             "author_email": "minsik.yoon@samsung.com",
             "committed_date": "2015-11-13T06:01:27.000+01:00",
             "committer_name": "윤민식",
-            "committer_email": "minsik.yoon@samsung.com"
+            "committer_email": "minsik.yoon@samsung.com",
+            "commit_author": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            },
+            "committer": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5771,7 +6283,15 @@
             "author_email": "minsik.yoon@samsung.com",
             "committed_date": "2015-11-13T06:00:16.000+01:00",
             "committer_name": "윤민식",
-            "committer_email": "minsik.yoon@samsung.com"
+            "committer_email": "minsik.yoon@samsung.com",
+            "commit_author": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            },
+            "committer": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5783,7 +6303,15 @@
             "author_email": "stanhu@gmail.com",
             "committed_date": "2015-11-13T05:23:14.000+01:00",
             "committer_name": "Stan Hu",
-            "committer_email": "stanhu@gmail.com"
+            "committer_email": "stanhu@gmail.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            },
+            "committer": {
+              "name": "Stan Hu",
+              "email": "stanhu@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5795,7 +6323,15 @@
             "author_email": "minsik.yoon@samsung.com",
             "committed_date": "2015-11-13T05:08:45.000+01:00",
             "committer_name": "윤민식",
-            "committer_email": "minsik.yoon@samsung.com"
+            "committer_email": "minsik.yoon@samsung.com",
+            "commit_author": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            },
+            "committer": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5807,7 +6343,15 @@
             "author_email": "minsik.yoon@samsung.com",
             "committed_date": "2015-11-13T05:08:04.000+01:00",
             "committer_name": "윤민식",
-            "committer_email": "minsik.yoon@samsung.com"
+            "committer_email": "minsik.yoon@samsung.com",
+            "commit_author": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            },
+            "committer": {
+              "name": "윤민식",
+              "email": "minsik.yoon@samsung.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5819,7 +6363,15 @@
             "author_email": "stanhu@packetzoom.com",
             "committed_date": "2015-08-25T17:53:12.000+02:00",
             "committer_name": "Stan Hu",
-            "committer_email": "stanhu@packetzoom.com"
+            "committer_email": "stanhu@packetzoom.com",
+            "commit_author": {
+              "name": "Stan Hu",
+              "email": "stanhu@packetzoom.com"
+            },
+            "committer": {
+              "name": "Stan Hu",
+              "email": "stanhu@packetzoom.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5831,7 +6383,15 @@
             "author_email": "sytse@gitlab.com",
             "committed_date": "2015-01-10T22:23:29.000+01:00",
             "committer_name": "Sytse Sijbrandij",
-            "committer_email": "sytse@gitlab.com"
+            "committer_email": "sytse@gitlab.com",
+            "commit_author": {
+              "name": "Sytse Sijbrandij",
+              "email": "sytse@gitlab.com"
+            },
+            "committer": {
+              "name": "Sytse Sijbrandij",
+              "email": "sytse@gitlab.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5843,7 +6403,15 @@
             "author_email": "marmis85@gmail.com",
             "committed_date": "2015-01-10T21:28:18.000+01:00",
             "committer_name": "marmis85",
-            "committer_email": "marmis85@gmail.com"
+            "committer_email": "marmis85@gmail.com",
+            "commit_author": {
+              "name": "marmis85",
+              "email": "marmis85@gmail.com"
+            },
+            "committer": {
+              "name": "marmis85",
+              "email": "marmis85@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5855,7 +6423,15 @@
             "author_email": "dmitriy.zaporozhets@gmail.com",
             "committed_date": "2014-02-27T10:01:38.000+01:00",
             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5867,7 +6443,15 @@
             "author_email": "dmitriy.zaporozhets@gmail.com",
             "committed_date": "2014-02-27T09:57:31.000+01:00",
             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5879,7 +6463,15 @@
             "author_email": "dmitriy.zaporozhets@gmail.com",
             "committed_date": "2014-02-27T09:54:21.000+01:00",
             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5891,7 +6483,15 @@
             "author_email": "dmitriy.zaporozhets@gmail.com",
             "committed_date": "2014-02-27T09:49:50.000+01:00",
             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
           },
           {
             "merge_request_diff_id": 10,
@@ -5903,7 +6503,15 @@
             "author_email": "dmitriy.zaporozhets@gmail.com",
             "committed_date": "2014-02-27T09:48:32.000+01:00",
             "committer_name": "Dmitriy Zaporozhets",
-            "committer_email": "dmitriy.zaporozhets@gmail.com"
+            "committer_email": "dmitriy.zaporozhets@gmail.com",
+            "commit_author": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            },
+            "committer": {
+              "name": "Dmitriy Zaporozhets",
+              "email": "dmitriy.zaporozhets@gmail.com"
+            }
           }
         ],
         "merge_request_diff_files": [
@@ -6348,7 +6956,15 @@
             "author_email": "james@jameslopez.es",
             "committed_date": "2016-01-19T15:44:02.000+01:00",
             "committer_name": "James Lopez",
-            "committer_email": "james@jameslopez.es"
+            "committer_email": "james@jameslopez.es",
+            "commit_author": {
+              "name": "James Lopez",
+              "email": "james@jameslopez.es"
+            },
+            "committer": {
+              "name": "James Lopez",
+              "email": "james@jameslopez.es"
+            }
           }
         ],
         "merge_request_diff_files": [

spec/lib/gitlab/background_migration/migrate_merge_request_diff_commit_users_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::BackgroundMigration::MigrateMergeRequestDiffCommitUsers do
+  let(:namespaces) { table(:namespaces) }
+  let(:projects) { table(:projects) }
+  let(:users) { table(:users) }
+  let(:merge_requests) { table(:merge_requests) }
+  let(:diffs) { table(:merge_request_diffs) }
+  let(:commits) do
+    table(:merge_request_diff_commits).tap do |t|
+      t.extend(SuppressCompositePrimaryKeyWarning)
+    end
+  end
+
+  let(:commit_users) { described_class::MergeRequestDiffCommitUser }
+
+  let(:namespace) { namespaces.create!(name: 'foo', path: 'foo') }
+  let(:project) { projects.create!(namespace_id: namespace.id) }
+  let(:merge_request) do
+    merge_requests.create!(
+      source_branch: 'x',
+      target_branch: 'master',
+      target_project_id: project.id
+    )
+  end
+
+  let(:diff) { diffs.create!(merge_request_id: merge_request.id) }
+  let(:migration) { described_class.new }
+
+  describe 'MergeRequestDiffCommit' do
+    describe '.each_row_to_migrate' do
+      it 'yields the rows to migrate for a given range' do
+        commit1 = commits.create!(
+          merge_request_diff_id: diff.id,
+          relative_order: 0,
+          sha: Gitlab::Database::ShaAttribute.serialize('123abc'),
+          author_name: 'bob',
+          author_email: 'bob@example.com',
+          committer_name: 'bob',
+          committer_email: 'bob@example.com'
+        )
+
+        commit2 = commits.create!(
+          merge_request_diff_id: diff.id,
+          relative_order: 1,
+          sha: Gitlab::Database::ShaAttribute.serialize('123abc'),
+          author_name: 'Alice',
+          author_email: 'alice@example.com',
+          committer_name: 'Alice',
+          committer_email: 'alice@example.com'
+        )
+
+        # We stub this constant to make sure we run at least two pagination
+        # queries for getting the data. This way we can test if the pagination
+        # is actually working properly.
+        stub_const(
+          'Gitlab::BackgroundMigration::MigrateMergeRequestDiffCommitUsers::COMMIT_ROWS_PER_QUERY',
+          1
+        )
+
+        rows = []
+
+        described_class::MergeRequestDiffCommit.each_row_to_migrate(diff.id, diff.id + 1) do |row|
+          rows << row
+        end
+
+        expect(rows.length).to eq(2)
+
+        expect(rows[0].author_name).to eq(commit1.author_name)
+        expect(rows[1].author_name).to eq(commit2.author_name)
+      end
+    end
+  end
+
+  describe 'MergeRequestDiffCommitUser' do
+    describe '.union' do
+      it 'produces a union of the given queries' do
+        alice = commit_users.create!(name: 'Alice', email: 'alice@example.com')
+        bob = commit_users.create!(name: 'Bob', email: 'bob@example.com')
+        users = commit_users.union([
+          commit_users.where(name: 'Alice').to_sql,
+          commit_users.where(name: 'Bob').to_sql
+        ])
+
+        expect(users).to include(alice)
+        expect(users).to include(bob)
+      end
+    end
+  end
+
+  describe '#perform' do
+    it 'migrates the data in the range' do
+      commits.create!(
+        merge_request_diff_id: diff.id,
+        relative_order: 0,
+        sha: Gitlab::Database::ShaAttribute.serialize('123abc'),
+        author_name: 'bob',
+        author_email: 'bob@example.com',
+        committer_name: 'bob',
+        committer_email: 'bob@example.com'
+      )
+
+      migration.perform(diff.id, diff.id + 1)
+
+      bob = commit_users.find_by(name: 'bob')
+      commit = commits.first
+
+      expect(commit.commit_author_id).to eq(bob.id)
+      expect(commit.committer_id).to eq(bob.id)
+    end
+
+    it 'treats empty names and Emails the same as NULL values' do
+      commits.create!(
+        merge_request_diff_id: diff.id,
+        relative_order: 0,
+        sha: Gitlab::Database::ShaAttribute.serialize('123abc'),
+        author_name: 'bob',
+        author_email: 'bob@example.com',
+        committer_name: '',
+        committer_email: ''
+      )
+
+      migration.perform(diff.id, diff.id + 1)
+
+      bob = commit_users.find_by(name: 'bob')
+      commit = commits.first
+
+      expect(commit.commit_author_id).to eq(bob.id)
+      expect(commit.committer_id).to be_nil
+    end
+
+    it 'does not update rows without a committer and author' do
+      commits.create!(
+        merge_request_diff_id: diff.id,
+        relative_order: 0,
+        sha: Gitlab::Database::ShaAttribute.serialize('123abc')
+      )
+
+      migration.perform(diff.id, diff.id + 1)
+
+      commit = commits.first
+
+      expect(commit_users.count).to eq(0)
+      expect(commit.commit_author_id).to be_nil
+      expect(commit.committer_id).to be_nil
+    end
+
+    it 'marks the background job as done' do
+      Gitlab::Database::BackgroundMigrationJob.create!(
+        class_name: 'MigrateMergeRequestDiffCommitUsers',
+        arguments: [diff.id, diff.id + 1]
+      )
+
+      migration.perform(diff.id, diff.id + 1)
+
+      job = Gitlab::Database::BackgroundMigrationJob.first
+
+      expect(job.status).to eq('succeeded')
+    end
+  end
+
+  describe '#get_data_to_update' do
+    it 'returns the users and commit rows to update' do
+      commits.create!(
+        merge_request_diff_id: diff.id,
+        relative_order: 0,
+        sha: Gitlab::Database::ShaAttribute.serialize('123abc'),
+        author_name: 'bob' + ('a' * 510),
+        author_email: 'bob@example.com',
+        committer_name: 'bob' + ('a' * 510),
+        committer_email: 'bob@example.com'
+      )
+
+      commits.create!(
+        merge_request_diff_id: diff.id,
+        relative_order: 1,
+        sha: Gitlab::Database::ShaAttribute.serialize('456abc'),
+        author_name: 'alice',
+        author_email: 'alice@example.com',
+        committer_name: 'alice',
+        committer_email: 'alice@example.com'
+      )
+
+      users, to_update = migration.get_data_to_update(diff.id, diff.id + 1)
+
+      bob_name = 'bob' + ('a' * 509)
+
+      expect(users).to include(%w[alice alice@example.com])
+      expect(users).to include([bob_name, 'bob@example.com'])
+
+      expect(to_update[[diff.id, 0]])
+        .to eq([[bob_name, 'bob@example.com'], [bob_name, 'bob@example.com']])
+
+      expect(to_update[[diff.id, 1]])
+        .to eq([%w[alice alice@example.com], %w[alice alice@example.com]])
+    end
+
+    it 'does not include a user if both the name and Email are missing' do
+      commits.create!(
+        merge_request_diff_id: diff.id,
+        relative_order: 0,
+        sha: Gitlab::Database::ShaAttribute.serialize('123abc'),
+        author_name: nil,
+        author_email: nil,
+        committer_name: 'bob',
+        committer_email: 'bob@example.com'
+      )
+
+      users, _ = migration.get_data_to_update(diff.id, diff.id + 1)
+
+      expect(users).to eq([%w[bob bob@example.com]].to_set)
+    end
+  end
+
+  describe '#get_user_rows_in_batches' do
+    it 'retrieves all existing users' do
+      alice = commit_users.create!(name: 'alice', email: 'alice@example.com')
+      bob = commit_users.create!(name: 'bob', email: 'bob@example.com')
+
+      users = [[alice.name, alice.email], [bob.name, bob.email]]
+      mapping = {}
+
+      migration.get_user_rows_in_batches(users, mapping)
+
+      expect(mapping[%w[alice alice@example.com]]).to eq(alice)
+      expect(mapping[%w[bob bob@example.com]]).to eq(bob)
+    end
+  end
+
+  describe '#create_missing_users' do
+    it 'creates merge request diff commit users that are missing' do
+      alice = commit_users.create!(name: 'alice', email: 'alice@example.com')
+      users = [%w[alice alice@example.com], %w[bob bob@example.com]]
+      mapping = { %w[alice alice@example.com] => alice }
+
+      migration.create_missing_users(users, mapping)
+
+      expect(mapping[%w[alice alice@example.com]]).to eq(alice)
+      expect(mapping[%w[bob bob@example.com]].name).to eq('bob')
+      expect(mapping[%w[bob bob@example.com]].email).to eq('bob@example.com')
+    end
+  end
+
+  describe '#update_commit_rows' do
+    it 'updates the merge request diff commit rows' do
+      to_update = { [42, 0] => [%w[alice alice@example.com], []] }
+      user_mapping = { %w[alice alice@example.com] => double(:user, id: 1) }
+
+      expect(migration)
+        .to receive(:bulk_update_commit_rows)
+        .with({ [42, 0] => [1, nil] })
+
+      migration.update_commit_rows(to_update, user_mapping)
+    end
+  end
+
+  describe '#bulk_update_commit_rows' do
+    context 'when there are no authors and committers' do
+      it 'does not update any rows' do
+        migration.bulk_update_commit_rows({ [1, 0] => [] })
+
+        expect(described_class::MergeRequestDiffCommit.connection)
+          .not_to receive(:execute)
+      end
+    end
+
+    context 'when there are only authors' do
+      it 'only updates the author IDs' do
+        author = commit_users.create!(name: 'Alice', email: 'alice@example.com')
+        commit = commits.create!(
+          merge_request_diff_id: diff.id,
+          relative_order: 0,
+          sha: Gitlab::Database::ShaAttribute.serialize('123abc')
+        )
+
+        mapping = {
+          [commit.merge_request_diff_id, commit.relative_order] =>
+            [author.id, nil]
+        }
+
+        migration.bulk_update_commit_rows(mapping)
+
+        commit = commits.first
+
+        expect(commit.commit_author_id).to eq(author.id)
+        expect(commit.committer_id).to be_nil
+      end
+    end
+
+    context 'when there are only committers' do
+      it 'only updates the committer IDs' do
+        committer =
+          commit_users.create!(name: 'Alice', email: 'alice@example.com')
+
+        commit = commits.create!(
+          merge_request_diff_id: diff.id,
+          relative_order: 0,
+          sha: Gitlab::Database::ShaAttribute.serialize('123abc')
+        )
+
+        mapping = {
+          [commit.merge_request_diff_id, commit.relative_order] =>
+            [nil, committer.id]
+        }
+
+        migration.bulk_update_commit_rows(mapping)
+
+        commit = commits.first
+
+        expect(commit.committer_id).to eq(committer.id)
+        expect(commit.commit_author_id).to be_nil
+      end
+    end
+
+    context 'when there are both authors and committers' do
+      it 'updates both the author and committer IDs' do
+        author = commit_users.create!(name: 'Bob', email: 'bob@example.com')
+        committer =
+          commit_users.create!(name: 'Alice', email: 'alice@example.com')
+
+        commit = commits.create!(
+          merge_request_diff_id: diff.id,
+          relative_order: 0,
+          sha: Gitlab::Database::ShaAttribute.serialize('123abc')
+        )
+
+        mapping = {
+          [commit.merge_request_diff_id, commit.relative_order] =>
+            [author.id, committer.id]
+        }
+
+        migration.bulk_update_commit_rows(mapping)
+
+        commit = commits.first
+
+        expect(commit.commit_author_id).to eq(author.id)
+        expect(commit.committer_id).to eq(committer.id)
+      end
+    end
+
+    context 'when there are multiple commit rows to update' do
+      it 'updates all the rows' do
+        author = commit_users.create!(name: 'Bob', email: 'bob@example.com')
+        committer =
+          commit_users.create!(name: 'Alice', email: 'alice@example.com')
+
+        commit1 = commits.create!(
+          merge_request_diff_id: diff.id,
+          relative_order: 0,
+          sha: Gitlab::Database::ShaAttribute.serialize('123abc')
+        )
+
+        commit2 = commits.create!(
+          merge_request_diff_id: diff.id,
+          relative_order: 1,
+          sha: Gitlab::Database::ShaAttribute.serialize('456abc')
+        )
+
+        mapping = {
+          [commit1.merge_request_diff_id, commit1.relative_order] =>
+            [author.id, committer.id],
+
+          [commit2.merge_request_diff_id, commit2.relative_order] =>
+            [author.id, nil]
+        }
+
+        migration.bulk_update_commit_rows(mapping)
+
+        commit1 = commits.find_by(relative_order: 0)
+        commit2 = commits.find_by(relative_order: 1)
+
+        expect(commit1.commit_author_id).to eq(author.id)
+        expect(commit1.committer_id).to eq(committer.id)
+
+        expect(commit2.commit_author_id).to eq(author.id)
+        expect(commit2.committer_id).to be_nil
+      end
+    end
+  end
+
+  describe '#primary_key' do
+    it 'returns the primary key for the commits table' do
+      key = migration.primary_key
+
+      expect(key.to_sql).to eq('("merge_request_diff_commits"."merge_request_diff_id", "merge_request_diff_commits"."relative_order")')
+    end
+  end
+
+  describe '#prepare' do
+    it 'trims a value to at most 512 characters' do
+      expect(migration.prepare('€' * 1_000)).to eq('€' * 512)
+    end
+
+    it 'returns nil if the value is an empty string' do
+      expect(migration.prepare('')).to be_nil
+    end
+  end
+end

spec/lib/gitlab/import_export/all_models.yml

@@ -198,6 +198,8 @@ merge_request_diff:
 - merge_request_diff_files
 merge_request_diff_commits:
 - merge_request_diff
+- commit_author
+- committer
 merge_request_diff_detail:
 - merge_request_diff
 merge_request_diff_files:

spec/lib/gitlab/import_export/import_test_coverage_spec.rb

@@ -109,14 +109,14 @@ RSpec.describe 'Test coverage of the Project Import' do
 
   def failure_message(not_tested_relations)
     <<~MSG
-      These relations seem to be added recenty and
+      These relations seem to be added recently and
       they expected to be covered in our Import specs: #{not_tested_relations}.
 
       To do that, expand one of the files listed in `project_json_fixtures`
       (or expand the list if you consider adding a new fixture file).
 
       After that, add a new spec into
-      `spec/lib/gitlab/import_export/project_tree_restorer_spec.rb`
+      `spec/lib/gitlab/import_export/project/tree_restorer_spec.rb`
       to check that the relation is being imported correctly.
 
       In case the spec breaks the master or there is a sense of urgency,

spec/lib/gitlab/import_export/project/object_builder_spec.rb

@@ -150,4 +150,30 @@ RSpec.describe Gitlab::ImportExport::Project::ObjectBuilder do
       expect(merge_request.persisted?).to be true
     end
   end
+
+  context 'merge request diff commit users' do
+    it 'finds the existing user' do
+      user = MergeRequest::DiffCommitUser
+        .find_or_create('Alice', 'alice@example.com')
+
+      found = described_class.build(
+        MergeRequest::DiffCommitUser,
+        'name' => 'Alice',
+        'email' => 'alice@example.com'
+      )
+
+      expect(found).to eq(user)
+    end
+
+    it 'creates a new user' do
+      found = described_class.build(
+        MergeRequest::DiffCommitUser,
+        'name' => 'Alice',
+        'email' => 'alice@example.com'
+      )
+
+      expect(found.name).to eq('Alice')
+      expect(found.email).to eq('alice@example.com')
+    end
+  end
 end

spec/lib/gitlab/import_export/project/tree_restorer_spec.rb

@@ -224,6 +224,27 @@ RSpec.describe Gitlab::ImportExport::Project::TreeRestorer do
           expect(MergeRequestDiffCommit.count).to eq(77)
         end
 
+        it 'assigns committer and author details to all diff commits' do
+          MergeRequestDiffCommit.all.each do |commit|
+            expect(commit.commit_author_id).not_to be_nil
+            expect(commit.committer_id).not_to be_nil
+          end
+        end
+
+        it 'assigns the correct commit users to different diff commits' do
+          commit1 = MergeRequestDiffCommit
+            .find_by(sha: '0b4bc9a49b562e85de7cc9e834518ea6828729b9')
+
+          commit2 = MergeRequestDiffCommit
+            .find_by(sha: 'a4e5dfebf42e34596526acb8611bc7ed80e4eb3f')
+
+          expect(commit1.commit_author.name).to eq('Dmitriy Zaporozhets')
+          expect(commit1.commit_author.email).to eq('dmitriy.zaporozhets@gmail.com')
+
+          expect(commit2.commit_author.name).to eq('James Lopez')
+          expect(commit2.commit_author.email).to eq('james@jameslopez.es')
+        end
+
         it 'has the correct data for merge request latest_merge_request_diff' do
           MergeRequest.find_each do |merge_request|
             expect(merge_request.latest_merge_request_diff_id).to eq(merge_request.merge_request_diffs.maximum(:id))

spec/lib/gitlab/import_export/safe_model_attributes.yml

@@ -235,6 +235,10 @@ MergeRequestDiffCommit:
 - committer_email
 - message
 - trailers
+MergeRequest::DiffCommitUser:
+- id
+- name
+- email
 MergeRequestDiffFile:
 - merge_request_diff_id
 - relative_order

spec/migrations/20210604133651_schedule_merge_request_diff_users_background_migration_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require_migration! 'schedule_merge_request_diff_users_background_migration'
+
+RSpec.describe ScheduleMergeRequestDiffUsersBackgroundMigration, :migration do
+  let(:migration) { described_class.new }
+
+  describe '#up' do
+    before do
+      allow(described_class::MergeRequestDiff)
+        .to receive(:minimum)
+        .with(:id)
+        .and_return(42)
+
+      allow(described_class::MergeRequestDiff)
+        .to receive(:maximum)
+        .with(:id)
+        .and_return(85_123)
+    end
+
+    it 'schedules the migrations in batches' do
+      expect(migration)
+        .to receive(:migrate_in)
+        .ordered
+        .with(2.minutes.to_i, described_class::MIGRATION_NAME, [42, 40_042])
+
+      expect(migration)
+        .to receive(:migrate_in)
+        .ordered
+        .with(4.minutes.to_i, described_class::MIGRATION_NAME, [40_042, 80_042])
+
+      expect(migration)
+        .to receive(:migrate_in)
+        .ordered
+        .with(6.minutes.to_i, described_class::MIGRATION_NAME, [80_042, 120_042])
+
+      migration.up
+    end
+
+    it 'creates rows to track the background migration jobs' do
+      expect(Gitlab::Database::BackgroundMigrationJob)
+        .to receive(:create!)
+        .ordered
+        .with(class_name: described_class::MIGRATION_NAME, arguments: [42, 40_042])
+
+      expect(Gitlab::Database::BackgroundMigrationJob)
+        .to receive(:create!)
+        .ordered
+        .with(class_name: described_class::MIGRATION_NAME, arguments: [40_042, 80_042])
+
+      expect(Gitlab::Database::BackgroundMigrationJob)
+        .to receive(:create!)
+        .ordered
+        .with(class_name: described_class::MIGRATION_NAME, arguments: [80_042, 120_042])
+
+      migration.up
+    end
+  end
+end

spec/models/merge_request/diff_commit_user_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe MergeRequest::DiffCommitUser do
+  describe 'validations' do
+    it 'requires that names are less than 512 characters long' do
+      expect(described_class.new(name: 'a' * 1000)).not_to be_valid
+    end
+
+    it 'requires that Emails are less than 512 characters long' do
+      expect(described_class.new(email: 'a' * 1000)).not_to be_valid
+    end
+
+    it 'requires either a name or Email' do
+      expect(described_class.new).not_to be_valid
+    end
+
+    it 'allows setting of just a name' do
+      expect(described_class.new(name: 'Alice')).to be_valid
+    end
+
+    it 'allows setting of just an Email' do
+      expect(described_class.new(email: 'alice@example.com')).to be_valid
+    end
+
+    it 'allows setting of both a name and Email' do
+      expect(described_class.new(name: 'Alice', email: 'alice@example.com'))
+        .to be_valid
+    end
+  end
+
+  describe '.prepare' do
+    it 'trims a value to at most 512 characters' do
+      expect(described_class.prepare('€' * 1_000)).to eq('€' * 512)
+    end
+
+    it 'returns nil if the value is an empty string' do
+      expect(described_class.prepare('')).to be_nil
+    end
+  end
+
+  describe '.find_or_create' do
+    it 'creates a new row if none exist' do
+      alice = described_class.find_or_create('Alice', 'alice@example.com')
+
+      expect(alice.name).to eq('Alice')
+      expect(alice.email).to eq('alice@example.com')
+    end
+
+    it 'returns an existing row if one exists' do
+      user1 = create(:merge_request_diff_commit_user)
+      user2 = described_class.find_or_create(user1.name, user1.email)
+
+      expect(user1).to eq(user2)
+    end
+
+    it 'handles concurrent inserts' do
+      user = create(:merge_request_diff_commit_user)
+
+      expect(described_class)
+        .to receive(:find_or_create_by!)
+        .ordered
+        .with(name: user.name, email: user.email)
+        .and_raise(ActiveRecord::RecordNotUnique)
+
+      expect(described_class)
+        .to receive(:find_or_create_by!)
+        .ordered
+        .with(name: user.name, email: user.email)
+        .and_return(user)
+
+      expect(described_class.find_or_create(user.name, user.email)).to eq(user)
+    end
+  end
+
+  describe '.bulk_find_or_create' do
+    it 'bulk creates missing rows and reuses existing rows' do
+      bob = create(
+        :merge_request_diff_commit_user,
+        name: 'Bob',
+        email: 'bob@example.com'
+      )
+
+      users = described_class.bulk_find_or_create(
+        [%w[Alice alice@example.com], %w[Bob bob@example.com]]
+      )
+      alice = described_class.find_by(name: 'Alice')
+
+      expect(users[%w[Alice alice@example.com]]).to eq(alice)
+      expect(users[%w[Bob bob@example.com]]).to eq(bob)
+    end
+
+    it 'does not insert any data when all users exist' do
+      bob = create(
+        :merge_request_diff_commit_user,
+        name: 'Bob',
+        email: 'bob@example.com'
+      )
+
+      users = described_class.bulk_find_or_create([%w[Bob bob@example.com]])
+
+      expect(described_class).not_to receive(:insert_all)
+      expect(users[%w[Bob bob@example.com]]).to eq(bob)
+    end
+
+    it 'handles concurrently inserted rows' do
+      bob = create(
+        :merge_request_diff_commit_user,
+        name: 'Bob',
+        email: 'bob@example.com'
+      )
+
+      input = [%w[Bob bob@example.com]]
+
+      expect(described_class)
+        .to receive(:bulk_find)
+        .twice
+        .with(input)
+        .and_return([], [bob])
+
+      users = described_class.bulk_find_or_create(input)
+
+      expect(users[%w[Bob bob@example.com]]).to eq(bob)
+    end
+  end
+end

spec/models/merge_request_diff_commit_spec.rb

@@ -16,6 +16,11 @@ RSpec.describe MergeRequestDiffCommit do
     let(:invalid_items_for_bulk_insertion) { [] } # class does not have any validations defined
   end
 
+  describe 'associations' do
+    it { is_expected.to belong_to(:commit_author) }
+    it { is_expected.to belong_to(:committer) }
+  end
+
   describe '#to_hash' do
     subject { merge_request.commits.first }
 
@@ -46,6 +51,8 @@ RSpec.describe MergeRequestDiffCommit do
           "committed_date": "2014-02-27T10:01:38.000+01:00".to_time,
           "committer_name": "Dmitriy Zaporozhets",
           "committer_email": "dmitriy.zaporozhets@gmail.com",
+          "commit_author_id": an_instance_of(Integer),
+          "committer_id": an_instance_of(Integer),
           "merge_request_diff_id": merge_request_diff_id,
           "relative_order": 0,
           "sha": Gitlab::Database::ShaAttribute.serialize("5937ac0a7beb003549fc5fd26fc247adbce4a52e"),
@@ -59,6 +66,8 @@ RSpec.describe MergeRequestDiffCommit do
           "committed_date": "2014-02-27T09:57:31.000+01:00".to_time,
           "committer_name": "Dmitriy Zaporozhets",
           "committer_email": "dmitriy.zaporozhets@gmail.com",
+          "commit_author_id": an_instance_of(Integer),
+          "committer_id": an_instance_of(Integer),
           "merge_request_diff_id": merge_request_diff_id,
           "relative_order": 1,
           "sha": Gitlab::Database::ShaAttribute.serialize("570e7b2abdd848b95f2f578043fc23bd6f6fd24d"),
@@ -76,6 +85,21 @@ RSpec.describe MergeRequestDiffCommit do
       subject
     end
 
+    it 'creates diff commit users' do
+      diff = create(:merge_request_diff, merge_request: merge_request)
+
+      described_class.create_bulk(diff.id, [commits.first])
+
+      commit_row = MergeRequestDiffCommit
+        .find_by(merge_request_diff_id: diff.id, relative_order: 0)
+
+      commit_user_row =
+        MergeRequest::DiffCommitUser.find_by(name: 'Dmitriy Zaporozhets')
+
+      expect(commit_row.commit_author).to eq(commit_user_row)
+      expect(commit_row.committer).to eq(commit_user_row)
+    end
+
     context 'with dates larger than the DB limit' do
       let(:commits) do
         # This commit's date is "Sun Aug 17 07:12:55 292278994 +0000"
@@ -92,6 +116,8 @@ RSpec.describe MergeRequestDiffCommit do
           "committed_date": timestamp,
           "committer_name": "Alejandro Rodríguez",
           "committer_email": "alejorro70@gmail.com",
+          "commit_author_id": an_instance_of(Integer),
+          "committer_id": an_instance_of(Integer),
           "merge_request_diff_id": merge_request_diff_id,
           "relative_order": 0,
           "sha": Gitlab::Database::ShaAttribute.serialize("ba3343bc4fa403a8dfbfcab7fc1a8c29ee34bd69"),
@@ -107,4 +133,28 @@ RSpec.describe MergeRequestDiffCommit do
       end
     end
   end
+
+  describe '.prepare_commits_for_bulk_insert' do
+    it 'returns the commit hashes and unique user tuples' do
+      commit = double(:commit, to_hash: {
+        parent_ids: %w[foo bar],
+        author_name: 'a' * 1000,
+        author_email: 'a' * 1000,
+        committer_name: 'Alice',
+        committer_email: 'alice@example.com'
+      })
+
+      hashes, tuples = described_class.prepare_commits_for_bulk_insert([commit])
+
+      expect(hashes).to eq([{
+        author_name: 'a' * 512,
+        author_email: 'a' * 512,
+        committer_name: 'Alice',
+        committer_email: 'alice@example.com'
+      }])
+
+      expect(tuples)
+        .to include(['a' * 512, 'a' * 512], %w[Alice alice@example.com])
+    end
+  end
 end