1 files changed, 35 insertions, 0 deletions
diff --git a/db/migrate/20200706035141_adjust_unique_index_alert_management_alerts.rb b/db/migrate/20200706035141_adjust_unique_index_alert_management_alerts.rb
new file mode 100644
index 00000000000..0a6e614be9a
--- /dev/null
+++ b/db/migrate/20200706035141_adjust_unique_index_alert_management_alerts.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+class AdjustUniqueIndexAlertManagementAlerts < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME        = false
+  INDEX_NAME      = 'index_alert_management_alerts_on_project_id_and_fingerprint'
+  NEW_INDEX_NAME  = 'index_partial_am_alerts_on_project_id_and_fingerprint'
+  RESOLVED_STATUS = 2
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index(:alert_management_alerts, %w(project_id fingerprint), where: "status <> #{RESOLVED_STATUS}", name: NEW_INDEX_NAME, unique: true, using: :btree)
+    remove_concurrent_index_by_name :alert_management_alerts, INDEX_NAME
+  end
+
+  def down
+    # Nullify duplicate fingerprints, except for the newest of each match (project_id, fingerprint).
+    query = <<-SQL
+      UPDATE alert_management_alerts am
+      SET fingerprint = NULL
+      WHERE am.created_at <>
+        (SELECT MAX(created_at)
+        FROM alert_management_alerts am2
+        WHERE am.fingerprint = am2.fingerprint AND am.project_id = am2.project_id)
+      AND am.fingerprint IS NOT NULL;
+    SQL
+
+    execute(query)
+
+    remove_concurrent_index_by_name :alert_management_alerts, NEW_INDEX_NAME
+    add_concurrent_index(:alert_management_alerts, %w(project_id fingerprint), name: INDEX_NAME, unique: true, using: :btree)
+  end
+end