1 files changed, 115 insertions, 0 deletions
diff --git a/db/post_migrate/20210731132939_backfill_stage_event_hash.rb b/db/post_migrate/20210731132939_backfill_stage_event_hash.rb
new file mode 100644
index 00000000000..2c4dc904387
--- /dev/null
+++ b/db/post_migrate/20210731132939_backfill_stage_event_hash.rb
@@ -0,0 +1,115 @@
+# frozen_string_literal: true
+
+class BackfillStageEventHash < ActiveRecord::Migration[6.1]
+  include Gitlab::Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  BATCH_SIZE = 100
+  EVENT_ID_IDENTIFIER_MAPPING = {
+    1 => :issue_created,
+    2 => :issue_first_mentioned_in_commit,
+    3 => :issue_closed,
+    4 => :issue_first_added_to_board,
+    5 => :issue_first_associated_with_milestone,
+    7 => :issue_last_edited,
+    8 => :issue_label_added,
+    9 => :issue_label_removed,
+    10 => :issue_deployed_to_production,
+    100 => :merge_request_created,
+    101 => :merge_request_first_deployed_to_production,
+    102 => :merge_request_last_build_finished,
+    103 => :merge_request_last_build_started,
+    104 => :merge_request_merged,
+    105 => :merge_request_closed,
+    106 => :merge_request_last_edited,
+    107 => :merge_request_label_added,
+    108 => :merge_request_label_removed,
+    109 => :merge_request_first_commit_at,
+    1000 => :code_stage_start,
+    1001 => :issue_stage_end,
+    1002 => :plan_stage_start
+  }.freeze
+
+  LABEL_BASED_EVENTS = Set.new([8, 9, 107, 108]).freeze
+
+  class GroupStage < ActiveRecord::Base
+    include EachBatch
+
+    self.table_name = 'analytics_cycle_analytics_group_stages'
+  end
+
+  class ProjectStage < ActiveRecord::Base
+    include EachBatch
+
+    self.table_name = 'analytics_cycle_analytics_project_stages'
+  end
+
+  class StageEventHash < ActiveRecord::Base
+    self.table_name = 'analytics_cycle_analytics_stage_event_hashes'
+  end
+
+  def up
+    GroupStage.reset_column_information
+    ProjectStage.reset_column_information
+    StageEventHash.reset_column_information
+
+    update_stage_table(GroupStage)
+    update_stage_table(ProjectStage)
+
+    add_not_null_constraint :analytics_cycle_analytics_group_stages, :stage_event_hash_id
+    add_not_null_constraint :analytics_cycle_analytics_project_stages, :stage_event_hash_id
+  end
+
+  def down
+    remove_not_null_constraint :analytics_cycle_analytics_group_stages, :stage_event_hash_id
+    remove_not_null_constraint :analytics_cycle_analytics_project_stages, :stage_event_hash_id
+  end
+
+  private
+
+  def update_stage_table(klass)
+    klass.each_batch(of: BATCH_SIZE) do |relation|
+      klass.transaction do
+        records = relation.where(stage_event_hash_id: nil).lock!.to_a # prevent concurrent modification (unlikely to happen)
+        records = delete_invalid_records(records)
+        next if records.empty?
+
+        hashes_by_stage = records.to_h { |stage| [stage, calculate_stage_events_hash(stage)] }
+        hashes = hashes_by_stage.values.uniq
+
+        StageEventHash.insert_all(hashes.map { |hash| { hash_sha256: hash } })
+
+        stage_event_hashes_by_hash = StageEventHash.where(hash_sha256: hashes).index_by(&:hash_sha256)
+        records.each do |stage|
+          stage.update!(stage_event_hash_id: stage_event_hashes_by_hash[hashes_by_stage[stage]].id)
+        end
+      end
+    end
+  end
+
+  def calculate_stage_events_hash(stage)
+    start_event_hash = calculate_event_hash(stage.start_event_identifier, stage.start_event_label_id)
+    end_event_hash = calculate_event_hash(stage.end_event_identifier, stage.end_event_label_id)
+
+    Digest::SHA256.hexdigest("#{start_event_hash}-#{end_event_hash}")
+  end
+
+  def calculate_event_hash(event_identifier, label_id = nil)
+    str = EVENT_ID_IDENTIFIER_MAPPING.fetch(event_identifier).to_s
+    str << "-#{label_id}" if LABEL_BASED_EVENTS.include?(event_identifier)
+
+    Digest::SHA256.hexdigest(str)
+  end
+
+  # Invalid records are safe to delete, since they are not working properly anyway
+  def delete_invalid_records(records)
+    to_be_deleted = records.select do |record|
+      EVENT_ID_IDENTIFIER_MAPPING[record.start_event_identifier].nil? ||
+        EVENT_ID_IDENTIFIER_MAPPING[record.end_event_identifier].nil?
+    end
+
+    to_be_deleted.each(&:delete)
+    records - to_be_deleted
+  end
+end