Add guides section on verbose query logs to Debugging

[olivierlacan]

Since this is a useful tool in debugging it made sense to document its existence and usage, especially in the console where it's disabled by default.

I also amended the Sending Messages section right above since it wasn't displaying query callers. Since they're enabled by default in 5.2 it felt appropriate to show them.

I might have to go through other guides to make sure we display them when appropriate if showing some logging.

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[rails-bot]

r? @schneems

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[schneems]

Hey! 👋 thanks for the PR!

Overall I like the idea of calling out this debugging feature! My only concern is that people might think that “random” is a method provided by active record if they are skimming. Can we be more explicit about calling it that it’s a user supplied method?

You can add “CI skip” to your commit to skip the tests.

[olivierlacan]

@schneems Looks like it was [ci skip] (brackets required) anywhere in the message title or body, so I accidentally triggered a few builds. My bad.

Great idea for the method. Changed it to Article.pamplemousse because now there's no way to think it could come from ActiveRecord... although it really really should. 😄

[schneems]

😂 love it. Thanks for the example!

[nickcoyne]

Just noticed a typo here: identity should be identify.

[olivierlacan]

Hey Nick, good catch. This PR is already merged though. Do you mind submitting another one to fix the typo? Thanks. :-)

…

On 4 November 2018 at 12:45:54, Nick Coyne ***@***.******@***.***)) wrote: @nickcoyne commented on this pull request. In guides/source/debugging_rails_applications.md(#34257 (comment)): > +After running `ActiveRecord::Base.verbose_query_logs = true` in the `rails console` session to enable verbose query logs and running the method again, it becomes obvious what single line of code is generating all these discrete database calls: + +``` +irb(main):003:0> Article.pamplemousse + Article Load (0.2ms) SELECT "articles".* FROM "articles" + ↳ app/models/article.rb:5 + Comment Load (0.1ms) SELECT "comments".* FROM "comments" WHERE "comments"."article_id" = ? [["article_id", 1]] + ↳ app/models/article.rb:6 + Comment Load (0.1ms) SELECT "comments".* FROM "comments" WHERE "comments"."article_id" = ? [["article_id", 2]] + ↳ app/models/article.rb:6 + Comment Load (0.1ms) SELECT "comments".* FROM "comments" WHERE "comments"."article_id" = ? [["article_id", 3]] + ↳ app/models/article.rb:6 +=> #<Comment id: 2, author: "1", body: "Well, actually...", article_id: 1, created_at: "2018-10-19 00:56:10", updated_at: "2018-10-19 00:56:10"> +``` + +Below each database statement you can see arrows pointing to the specific source filename (and line number) of the method that resulted in a database call. This can help you identity and address performance problems caused by N+1 queries: single database queries that generates multiple additional queries. Just noticed a typo here: identity should be identify. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub(#34257 (review)), or mute the thread(https://github.com/notifications/unsubscribe-auth/AAEBntdEVeyatOJ8CgtukXID0hZsLbdBks5uryfSgaJpZM4XvkjH).