Use new index name and create before removing

db/migrate/20200706035141_adjust_unique_index_alert_management_alerts.rb

@@ -5,17 +5,18 @@ class AdjustUniqueIndexAlertManagementAlerts < ActiveRecord::Migration[6.0]
 
   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
 
   # rubocop:disable Migration/RemoveIndex
   # rubocop:disable Migration/AddIndex
   def up
+    add_index(:alert_management_alerts, %w(project_id fingerprint), where: "status <> '#{RESOLVED_STATUS}'", name: NEW_INDEX_NAME, unique: true, using: :btree)
     remove_index :alert_management_alerts, name: INDEX_NAME
-    add_index(:alert_management_alerts, %w(project_id fingerprint), where: "status <> '#{RESOLVED_STATUS}'", name: INDEX_NAME, unique: true, using: :btree)
   end
 
   def down
-    remove_index :alert_management_alerts, name: INDEX_NAME
+    remove_index :alert_management_alerts, name: NEW_INDEX_NAME
     add_index(:alert_management_alerts, %w(project_id fingerprint), name: INDEX_NAME, unique: true, using: :btree)
   end
   # rubocop:enable Migration/RemoveIndex

db/structure.sql

@@ -18695,8 +18695,6 @@ CREATE INDEX index_alert_management_alerts_on_environment_id ON public.alert_man
 
 CREATE INDEX index_alert_management_alerts_on_issue_id ON public.alert_management_alerts USING btree (issue_id);
 
-CREATE UNIQUE INDEX index_alert_management_alerts_on_project_id_and_fingerprint ON public.alert_management_alerts USING btree (project_id, fingerprint) WHERE (status <> '2'::smallint);
-
 CREATE UNIQUE INDEX index_alert_management_alerts_on_project_id_and_iid ON public.alert_management_alerts USING btree (project_id, iid);
 
 CREATE INDEX index_alert_management_alerts_on_prometheus_alert_id ON public.alert_management_alerts USING btree (prometheus_alert_id) WHERE (prometheus_alert_id IS NOT NULL);
@@ -19945,6 +19943,8 @@ CREATE INDEX index_pages_domains_on_verified_at_and_enabled_until ON public.page
 
 CREATE INDEX index_pages_domains_on_wildcard ON public.pages_domains USING btree (wildcard);
 
+CREATE UNIQUE INDEX index_partial_am_alerts_on_project_id_and_fingerprint ON public.alert_management_alerts USING btree (project_id, fingerprint) WHERE (status <> '2'::smallint);
+
 CREATE UNIQUE INDEX index_partitioned_foreign_keys_unique_index ON public.partitioned_foreign_keys USING btree (to_table, from_table, from_column);
 
 CREATE INDEX index_pat_on_user_id_and_expires_at ON public.personal_access_tokens USING btree (user_id, expires_at);