1 files changed, 73 insertions, 0 deletions
diff --git a/lib/gitlab/background_migration/backfill_work_item_type_id_for_issues.rb b/lib/gitlab/background_migration/backfill_work_item_type_id_for_issues.rb
new file mode 100644
index 00000000000..a16efa4222b
--- /dev/null
+++ b/lib/gitlab/background_migration/backfill_work_item_type_id_for_issues.rb
@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module BackgroundMigration
+    # Backfills the `issues.work_item_type_id` column, replacing any
+    # instances of `NULL` with the appropriate `work_item_types.id` based on `issues.issue_type`
+    class BackfillWorkItemTypeIdForIssues
+      # Basic AR model for issues table
+      class MigrationIssue < ApplicationRecord
+        include ::EachBatch
+
+        self.table_name = 'issues'
+
+        scope :base_query, ->(base_type) { where(work_item_type_id: nil, issue_type: base_type) }
+      end
+
+      MAX_UPDATE_RETRIES = 3
+
+      def perform(start_id, end_id, batch_table, batch_column, sub_batch_size, pause_ms, base_type, base_type_id)
+        parent_batch_relation = relation_scoped_to_range(batch_table, batch_column, start_id, end_id, base_type)
+
+        parent_batch_relation.each_batch(column: batch_column, of: sub_batch_size) do |sub_batch|
+          first, last = sub_batch.pluck(Arel.sql('min(id), max(id)')).first
+
+          # The query need to be reconstructed because .each_batch modifies the default scope
+          # See: https://gitlab.com/gitlab-org/gitlab/-/issues/330510
+          reconstructed_sub_batch = MigrationIssue.unscoped.base_query(base_type).where(id: first..last)
+
+          batch_metrics.time_operation(:update_all) do
+            update_with_retry(reconstructed_sub_batch, base_type_id)
+          end
+
+          pause_ms = 0 if pause_ms < 0
+          sleep(pause_ms * 0.001)
+        end
+      end
+
+      def batch_metrics
+        @batch_metrics ||= Gitlab::Database::BackgroundMigration::BatchMetrics.new
+      end
+
+      private
+
+      # Retry mechanism required as update statements on the issues table will randomly take longer than
+      # expected due to gin indexes https://gitlab.com/gitlab-org/gitlab/-/merge_requests/71869#note_775796352
+      def update_with_retry(sub_batch, base_type_id)
+        update_attempt = 1
+
+        begin
+          update_batch(sub_batch, base_type_id)
+        rescue ActiveRecord::StatementTimeout, ActiveRecord::QueryCanceled => e
+          update_attempt += 1
+
+          if update_attempt <= MAX_UPDATE_RETRIES
+            # sleeping 30 seconds as it might take a long time to clean the gin index pending list
+            sleep(30)
+            retry
+          end
+
+          raise e
+        end
+      end
+
+      def update_batch(sub_batch, base_type_id)
+        sub_batch.update_all(work_item_type_id: base_type_id)
+      end
+
+      def relation_scoped_to_range(source_table, source_key_column, start_id, end_id, base_type)
+        MigrationIssue.where(source_key_column => start_id..end_id).base_query(base_type)
+      end
+    end
+  end
+end