Mongoid 没有性能问题

昨天台湾的朋友发布了一篇将 ruby-china 代码迁移成从 Mongoid 迁移成 ActiveRecord 的文章,其中有提到 Mongoid 效率的问题。我认为多少有些对于 Mongoid 的误解,所以在此撰写这篇文章做一些解释,以免大家误解 Mongoid 效率不好。

对比两个不同版本的差距

我昨晚特意下载了他们重构成 MySQL 版本的 ruby-taiwan 的代码与目前 ruby-china 的代码在开发环境下面模拟数据做了一下对比.

数据场景

  • MongoDb 的数据基本和目前 Ruby China 上面类似,而 MySQL 的测试数据只是简单的添加了足够的条数。
  • 开发环境下面,没有开启任何 cache
  • ruby-1.9.3-p0-falcon

对比结果:

  • 话题列表 /topics (15个话题)
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# ActiveRecord
Completed 200 OK in 179ms (Views: 169.0ms | ActiveRecord: 9.2ms)
Completed 200 OK in 177ms (Views: 167.4ms | ActiveRecord: 8.1ms)
Completed 200 OK in 116ms (Views: 105.5ms | ActiveRecord: 8.3ms)
Completed 200 OK in 110ms (Views: 99.2ms | ActiveRecord: 9.6ms)
Completed 200 OK in 191ms (Views: 181.5ms | ActiveRecord: 8.5ms)
Completed 200 OK in 192ms (Views: 180.7ms | ActiveRecord: 10.2ms)

# Mongoid
Completed 200 OK in 192ms (Views: 117.4ms | Mongo: 73.8ms | Solr: 0.0ms)
Completed 200 OK in 378ms (Views: 298.9ms | Mongo: 77.8ms | Solr: 0.0ms)
Completed 200 OK in 214ms (Views: 138.7ms | Mongo: 73.9ms | Solr: 0.0ms)
Completed 200 OK in 185ms (Views: 120.9ms | Mongo: 63.0ms | Solr: 0.0ms)
Completed 200 OK in 186ms (Views: 122.2ms | Mongo: 63.0ms | Solr: 0.0ms)
Completed 200 OK in 207ms (Views: 140.1ms | Mongo: 66.0ms | Solr: 0.0ms)
  • 话题查看页面 /topics/:id 27条回复的场景

由于两边 Markdown 的算法不同,我把 Markdown 功能关闭了的,其他逻辑几乎相同

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# ActiveRecord
Completed 200 OK in 283ms (Views: 263.2ms | ActiveRecord: 5.5ms)
Completed 200 OK in 282ms (Views: 260.4ms | ActiveRecord: 5.8ms)
Completed 200 OK in 284ms (Views: 262.6ms | ActiveRecord: 5.3ms)
Completed 200 OK in 283ms (Views: 262.7ms | ActiveRecord: 5.0ms)
Completed 200 OK in 191ms (Views: 170.3ms | ActiveRecord: 5.1ms)
Completed 200 OK in 195ms (Views: 174.5ms | ActiveRecord: 5.3ms)

# Mongoid
Completed 200 OK in 119ms (Views: 93.6ms | Mongo: 5.5ms | Solr: 3.2ms)
Completed 200 OK in 176ms (Views: 150.8ms | Mongo: 6.0ms | Solr: 3.3ms)
Completed 200 OK in 115ms (Views: 90.9ms | Mongo: 6.6ms | Solr: 3.4ms)
Completed 200 OK in 115ms (Views: 91.9ms | Mongo: 6.4ms | Solr: 3.7ms)
Completed 200 OK in 119ms (Views: 93.4ms | Mongo: 5.0ms | Solr: 6.1ms)
Completed 200 OK in 121ms (Views: 97.9ms | Mongo: 5.6ms | Solr: 3.3ms)

以上两个页面的测试数据表示,ActiveRecord 并没有 @xdite 声称的从 400ms 减少到 90ms 这么大的差距,虽然 Mongoid 确实是有一些慢,但是差距实际上是不大的。

实际 ruby-china.org 产品环境的运行数据 (有 cache)

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Started GET "/topics/777" (58条回复)
Completed 200 OK in 107ms (Views: 82.9ms | Mongo: 23.3ms | Solr: 0.0ms)
Completed 200 OK in 121ms (Views: 33.7ms | Mongo: 27.5ms | Solr: 0.0ms)
Completed 200 OK in 135ms (Views: 48.4ms | Mongo: 26.8ms | Solr: 0.0ms)

Started GET "/topics"
Completed 200 OK in 104ms (Views: 80.5ms | Mongo: 22.1ms | Solr: 0.0ms)
Completed 200 OK in 108ms (Views: 83.9ms | Mongo: 22.7ms | Solr: 0.0ms)
Completed 200 OK in 107ms (Views: 82.9ms | Mongo: 22.5ms | Solr: 0.0ms)
Completed 200 OK in 143ms (Views: 92.2ms | Mongo: 49.1ms | Solr: 0.0ms)
Completed 200 OK in 108ms (Views: 84.5ms | Mongo: 22.3ms | Solr: 0.0ms)

之前慢的原因解释

之前 ruby-china 某个时期在开发环境下面确实非常慢,但那个原因是下面几个

  1. will_paginate 由于不支持 MongoDb 的分页方式,所以每次分页都是 Model.all 以后,以 Array 来分页的,所以这个是之前性能的罪魁祸首,参见
  2. Mongoid 的 eager loading 需要手动配置 identity_map_enabled: true 才会有效果;
  3. 之前 Rails 3.1 环境确实比较慢,已进入 Rails 3.2 已经感觉是非常明显的。

总结

总的来说,MongoDb 是非常不错的,而 Mongoid 长远来看也是值得使用的 Gem,虽然目前阶段它还不够完美,但是也不至于我们将他抛弃。 我目前对于 MongoDb 的 schema-less 特性目前也是我比较困扰的地方,数据结构变化需要非常小心,这个需要经验。 请不要误解 Mongoid 有性能问题。