1 files changed, 71 insertions, 0 deletions
diff --git a/db/post_migrate/20210226141517_dedup_issue_metrics.rb b/db/post_migrate/20210226141517_dedup_issue_metrics.rb
new file mode 100644
index 00000000000..8228d509e07
--- /dev/null
+++ b/db/post_migrate/20210226141517_dedup_issue_metrics.rb
@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+class DedupIssueMetrics < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  TMP_INDEX_NAME = 'tmp_unique_issue_metrics_by_issue_id'
+  OLD_INDEX_NAME = 'index_issue_metrics'
+  INDEX_NAME = 'index_unique_issue_metrics_issue_id'
+  BATCH_SIZE = 1_000
+
+  disable_ddl_transaction!
+
+  class IssueMetrics < ActiveRecord::Base
+    self.table_name = 'issue_metrics'
+
+    include EachBatch
+  end
+
+  def up
+    IssueMetrics.reset_column_information
+
+    last_metrics_record_id = IssueMetrics.maximum(:id) || 0
+
+    # This index will disallow further duplicates while we're deduplicating the data.
+    add_concurrent_index(:issue_metrics, :issue_id, where: "id > #{Integer(last_metrics_record_id)}", unique: true, name: TMP_INDEX_NAME)
+
+    IssueMetrics.each_batch(of: BATCH_SIZE) do |relation|
+      duplicated_issue_ids = IssueMetrics
+        .where(issue_id: relation.select(:issue_id))
+        .select(:issue_id)
+        .group(:issue_id)
+        .having('COUNT(issue_metrics.issue_id) > 1')
+        .pluck(:issue_id)
+
+      duplicated_issue_ids.each do |issue_id|
+        deduplicate_item(issue_id)
+      end
+    end
+
+    add_concurrent_index(:issue_metrics, :issue_id, unique: true, name: INDEX_NAME)
+    remove_concurrent_index_by_name(:issue_metrics, TMP_INDEX_NAME)
+    remove_concurrent_index_by_name(:issue_metrics, OLD_INDEX_NAME)
+  end
+
+  def down
+    add_concurrent_index(:issue_metrics, :issue_id, name: OLD_INDEX_NAME)
+    remove_concurrent_index_by_name(:issue_metrics, TMP_INDEX_NAME)
+    remove_concurrent_index_by_name(:issue_metrics, INDEX_NAME)
+  end
+
+  private
+
+  def deduplicate_item(issue_id)
+    issue_metrics_records = IssueMetrics.where(issue_id: issue_id).order(updated_at: :asc).to_a
+
+    attributes = {}
+    issue_metrics_records.each do |issue_metrics_record|
+      params = issue_metrics_record.attributes.except('id')
+      attributes.merge!(params.compact)
+    end
+
+    ActiveRecord::Base.transaction do
+      record_to_keep = issue_metrics_records.pop
+      records_to_delete = issue_metrics_records
+
+      IssueMetrics.where(id: records_to_delete.map(&:id)).delete_all
+      record_to_keep.update!(attributes)
+    end
+  end
+end