PostgreSQL查询导致cpu峰值达到100％.给出90k记录,是7000的成本

EXPLAIN ANALYZE SELECT  "delayed_jobs".*
FROM "delayed_jobs"
WHERE ((run_at <= '2011-05-23 15:16:43.180810' AND (locked_at IS NULL OR locked_at < '2011-01-25 11:05:28.077144') OR locked_by = 'host:foo pid:2') AND failed_at IS NULL AND queue = 'authentication_emails')
ORDER BY priority ASC,run_at ASC LIMIT 5

要么：

EXPLAIN ANALYZE SELECT  "delayed_jobs".*
FROM "delayed_jobs"
WHERE ((run_at <= '2011-05-23 15:16:43.180810' AND (locked_at IS NULL OR locked_at < '2011-01-25 11:05:28.077144') OR locked_by = 'host:foo pid:2') AND failed_at IS NULL )
ORDER BY priority ASC,run_at ASC LIMIT 5

对于第一个查询,输出等于：

Limit  (cost=7097.57..7097.57 rows=1 width=1008) (actual time=35.657..35.657 rows=0 loops=1)
  ->  Sort  (cost=7097.57..7097.57 rows=1 width=1008) (actual time=35.655..35.655 rows=0 loops=1)
        Sort Key: priority,run_at
        Sort Method: quicksort  Memory: 25kB
        ->  Seq Scan on delayed_jobs  (cost=0.00..7097.56 rows=1 width=1008) (actual time=35.648..35.648 rows=0 loops=1)
              Filter: ((failed_at IS NULL) AND ((queue)::text = 'authentication_emails'::text) AND (((run_at <= '2011-05-23 15:16:43.18081'::timestamp without time zone) AND ((locked_at IS NULL) OR (locked_at < '2011-01-25 11:05:28.077144'::timestamp without time zone))) OR (locked_by = 'host:foo pid:2'::text)))
Total runtime: 35.695 ms

该表目前有90k记录,范围从0到200k.我们注意到这个查询导致CPU出现峰值并导致瓶颈.从上面的解释信息中可以学到什么.索引应该添加到哪里？谢谢

DB Schema ..表有0个索引.

create_table "delayed_jobs",:force => true do |t|
    t.integer  "priority",:default => 0
    t.integer  "attempts",:default => 0
    t.text     "handler"
    t.text     "last_error"
    t.datetime "run_at"
    t.datetime "locked_at"
    t.datetime "failed_at"
    t.text     "locked_by"
    t.datetime "created_at",:null => false
    t.datetime "updated_at",:null => false
    t.string   "queue"
  end