alter table pgbench_accounts add mtime timestamp default now();
create or replace function fill_mtime() returns trigger as $$begin NEW.mtime=now(); return NEW; END;$$ language plpgsql;
create trigger t_accounts_mtime before update on pgbench_accounts for each row execute function fill_mtime();
create index accounts_mtime on pgbench_accounts (mtime, aid);
create index fiver on pgbench_accounts ((aid - (aid%5)));
create index tenner on pgbench_accounts ((aid - (aid%10)));
create index score on pgbench_accounts ((aid - (aid%20)));
ANALYZE pgbench_accounts;