CODEWITHSUNDEEP
ruby-on-railsrubyimpressionist
VegaStudios
VegaStudios

Reputation: 324

Remove N+1 queries for impressionist gem

In my Rails app I have the N+1 problem where I'm making extra call(s) to the database to get associated data over and over again, specially when logging impressions per model.

For example:

Started GET "/" for 127.0.0.1 at 2018-12-02 16:21:05 -0500
Processing by JobsController#index as HTML
  Job Load (4.4ms)  SELECT  "jobs".* FROM "jobs" WHERE "jobs"."published_at" IS NOT NULL ORDER BY "jobs"."published_at" DESC LIMIT $1 OFFSET $2  [["LIMIT", 30], ["OFFSET", 0]]
  ↳ app/controllers/jobs_controller.rb:22
  User Load (1.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 ORDER BY "users"."id" ASC LIMIT $2  [["id", 13], ["LIMIT", 1]]
  ↳ app/controllers/jobs_controller.rb:24
  Impression Exists (1.3ms)  SELECT  1 AS one FROM "impressions" WHERE "impressions"."impressionable_id" = $1 AND "impressions"."impressionable_type" = $2 AND "impressions"."session_hash" = $3 LIMIT $4  [["impressionable_id", 705], ["impressionable_type", "Job"], ["session_hash", "d80d52dd401011a626d600167140e49f"], ["LIMIT", 1]]
  ↳ app/controllers/jobs_controller.rb:24
  Impression Exists (0.6ms)  SELECT  1 AS one FROM "impressions" WHERE "impressions"."impressionable_id" = $1 AND "impressions"."impressionable_type" = $2 AND "impressions"."session_hash" = $3 LIMIT $4  [["impressionable_id", 704], ["impressionable_type", "Job"], ["session_hash", "d80d52dd401011a626d600167140e49f"], ["LIMIT", 1]]
  ↳ app/controllers/jobs_controller.rb:24
  Impression Exists (0.4ms)  SELECT  1 AS one FROM "impressions" WHERE "impressions"."impressionable_id" = $1 AND "impressions"."impressionable_type" = $2 AND "impressions"."session_hash" = $3 LIMIT $4  [["impressionable_id", 703], ["impressionable_type", "Job"], ["session_hash", "d80d52dd401011a626d600167140e49f"], ["LIMIT", 1]]
  ↳ app/controllers/jobs_controller.rb:24

I'm using the impressionist gem and using the impressionist method directly, taking all of the Jobs on the page and logging an impression. The problem is because I'm only recording unique impressions, for records that already have an impression, these additional calls are redundant. I tried to use @jobs.includes(:impressions).each to preload the associated data hoping Rails was smart enough to figure out which records existed, but Rails still outputs numerous Impression Exists queries.

@jobs.each{|job| impressionist(job,'', :unique => [:session_hash])}

Upvotes: 0

Views: 113

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