Drop temporary index on ci builds

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/295477

changelogs/unreleased/ab-drop-tmp-index.yml

+---
+title: Drop temporary index on ci_builds
+merge_request: 50961
+author:
+type: other

db/migrate/20210102164121_drop_temporary_index_on_ci_builds.rb

+# frozen_string_literal: true
+
+class DropTemporaryIndexOnCiBuilds < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  INDEX = 'tmp_build_stage_position_index'.freeze
+
+  def up
+    remove_concurrent_index_by_name :ci_builds, INDEX
+  end
+
+  def down
+    add_concurrent_index :ci_builds, [:stage_id, :stage_idx], where: 'stage_idx IS NOT NULL', name: INDEX
+  end
+end

db/schema_migrations/20210102164121

+d15dc3e57f050f037dd6b6b2b1efdafee49bf411580e35a7b4dbe14868c41e13
\ No newline at end of file

db/structure.sql

@@ -23105,8 +23105,6 @@ CREATE INDEX temporary_index_vulnerabilities_on_id ON vulnerabilities USING btre
 
 CREATE UNIQUE INDEX term_agreements_unique_index ON term_agreements USING btree (user_id, term_id);
 
-CREATE INDEX tmp_build_stage_position_index ON ci_builds USING btree (stage_id, stage_idx) WHERE (stage_idx IS NOT NULL);
-
 CREATE INDEX tmp_index_for_email_unconfirmation_migration ON emails USING btree (id) WHERE (confirmed_at IS NOT NULL);
 
 CREATE INDEX tmp_index_on_vulnerabilities_non_dismissed ON vulnerabilities USING btree (id) WHERE (state <> 2);