Ruby on rails 如何知道Memcached是否用作我的Rails.cache？

我试图在DigitalOcean上的Ubuntu 14.04机器上实现缓存，我不确定是否正确设置了缓存。我在Rails控制台中看到：

[2] pry(#<DigitizationsController>)> Rails.cache.write("hi", 1)
Cache write: hi
=> 288230376151711744
[3] pry(#<DigitizationsController>)> Rails.cache.read("hi")
Cache read: hi
=> 1
[4] pry(#<DigitizationsController>)> Rails.cache.class
=> ActiveSupport::Cache::DalliStore

我的终端输出似乎是从缓存中获取的，但是为什么之后会触发查询呢

Rails.cache.read('digitizations_index')
Cache read: digitizations_index
  ActsAsTaggableOn::Tag Load (0.6ms)  SELECT  tags.*, taggings.tags_count AS count FROM `tags` JOIN (SELECT taggings.tag_id, COUNT(taggings.tag_id) AS tags_count FROM `taggings` INNER JOIN submissions ON submissions.id = taggings.taggable_id WHERE (taggings.taggable_type = 'Submission' AND taggings.context = 'tags') AND (taggings.taggable_id IN (NULL)) GROUP BY taggings.tag_id HAVING COUNT(taggings.tag_id) > 0) AS taggings ON taggings.tag_id = tags.id WHERE (taggings_count > 5)  ORDER BY RAND() LIMIT 5

为什么数据库查询在命中缓存时会触发？这是因为我只缓存查询计划，当我实际调用变量时，还是当我在控制台中调用查询计划时，它会触发，而控制台会调用

我的环境有以下几行：

config.cache_store = :dalli_store

在开发过程中，我也看到了这个错误。有人知道为什么吗？我的猜测是，在开发中，我并不急于加载

 Rails.cache.read('digitizations_index')
 Cache read: digitizations_index
 Unexpected exception during Dalli request: NameError: uninitialized constant ActsAsTaggableOn::Taggable::Collection

至于为什么memcached仍在运行查询，我的猜测是，我只是在缓存查询计划，一旦调用变量，查询计划就会延迟计算。
 Rails.cache.read('digitizations_index')
 Cache read: digitizations_index
 Unexpected exception during Dalli request: NameError: uninitialized constant ActsAsTaggableOn::Taggable::Collection