Anya/375 sikekiq not found

[anyakhvost]

connects #375

1. Record not found issue - Sidekiq is finding out about the job before the database record has it committed, so use after_commit on: :create.
2. Add test_after_commit gem to actually test after_commit hook in rspec.

[amprokop]

@aroltsch — can we add a little bit of context on how this connects to #375 ? is there a recommended way we can test that this addresses the issue/how did you discover the fix?

[amprokop]

nit: this verb tense may not clearly show the meaning after this is merged.

Suggest something more like To prevent Sidekiq from finding out...

And maybe we can post that SO link too?

[anyakhvost]

@amprokop
I think here is what happens: Active Record starts to create a download in the DB. Then immediately we fire up the Sidekiq job to use that download record. The Sidekiq job is a separate process so it cannot use the same in-memory download from the rails application so it goes to the DB to look for it. When it goes to look for it, the download record is not committed yet in the DB so it fails to find the record. Hence we get these logs:
Record not found... Exception ActiveRecord::RecordNotFound: Couldn't find Download with 'id'=xxx
The fix is to fire up the Sidekiq job after the record has been committed to the DB.
The issue was happening randomly so in order to test it, the QA person would need to try a bunch of downloads and see if it happens again.