通过计数查询加速Active Record组

Question

How can I speed up the following query? I'm look to find record with 6 or less unique values of fb_id . The select doesn't seem to be adding much in terms of time but instead it's the group and count . Is there an alternate way to query? I added an index on fb_id and it only sped up the query by 50%

FbGroupApplication.group(:fb_id).where.not(
  fb_id: _get_exclude_fb_group_ids
).group(
  "count_fb_id desc"
).count(
  "fb_id"
).select{|k, v| v <= 6 }

The query is looking for FbGroupApplications that have 6 or less applications to the same fb_id

Answer 1

Passing a block to the select method made Rails trigger the SQL, convert the found rows into ActiveRecord::Base's ruby object (record), and then perform a select on the array based of the block you gave. This whole process is costly (ruby is not good at this).

You can "delegate" the responsibility of comparing the count vs 6 to the database with a having clause:

FbGroupApplication
  .group(:fb_id)
  .where.not(fb_id: _get_exclude_fb_group_ids)
  .having('count(fb_id) <= 6')