ruby-on-rails - 简单的 Postgres 查询在 Heroku 上运行缓慢

Question

我有一个包含大约 15,000 个项目的 Movie 模型和一个包含 3500 个项目的 Dvd 模型。

以下查询是使用在 Heroku 上运行的 Crane Postgres 数据库的简单 Rails 关联。我想知道为什么以下查询需要这么长时间，我最终如何才能减少它的时间。

2012-10-24T05:42:19+00:00 app[postgres]: [30-1] [BLACK] LOG:  duration: 57.914 ms  statement: SELECT  "movies".* FROM "movies"  WHERE "movies"."dvd_id" = 37 ORDER BY scene LIMIT 1
2012-10-24T05:42:20+00:00 app[postgres]: [31-1] [BLACK] LOG:  duration: 77.086 ms  statement: SELECT  "movies".* FROM "movies"  WHERE "movies"."dvd_id" = 915 ORDER BY scene LIMIT 1
2012-10-24T05:42:20+00:00 app[postgres]: [32-1] [BLACK] LOG:  duration: 85.602 ms  statement: SELECT  "movies".* FROM "movies"  WHERE "movies"."dvd_id" = 108 ORDER BY scene LIMIT 1
2012-10-24T05:42:21+00:00 app[postgres]: [33-1] [BLACK] LOG:  duration: 70.147 ms  statement: SELECT  "movies".* FROM "movies"  WHERE "movies"."dvd_id" = 11 ORDER BY scene LIMIT 1
2012-10-24T05:42:21+00:00 app[postgres]: [34-1] [BLACK] LOG:  duration: 144.204 ms  statement: SELECT  "movies".* FROM "movies"  WHERE "movies"."dvd_id" = 6 ORDER BY scene LIMIT 1
2012-10-24T05:42:22+00:00 app[postgres]: [35-1] [BLACK] LOG:  duration: 56.623 ms  statement: SELECT  "movies".* FROM "movies"  WHERE "movies"."dvd_id" = 1956 ORDER BY scene LIMIT 1
2012-10-24T05:42:23+00:00 app[postgres]: [36-1] [BLACK] LOG:  duration: 64.860 ms  statement: SELECT  "movies".* FROM "movies"  WHERE "movies"."dvd_id" = 747 ORDER BY scene LIMIT 1

Answer 1

您可以直接连接到您的数据库 CLI，然后使用 PostgresQL EXPLAIN 命令获取有关它如何运行您的查询的信息。这可以显示可以向表中添加索引以加快处理速度的位置。 Postgres docs更详细地解释(看到我在那里做了什么？)EXPLAIN。