Resque jobs failing for missing AR connection on Rails 5.2

[CodingAnarchy]

Steps to reproduce

Queue enough resque jobs that have to connect to the database, and this appears to occur sporadically. I haven't been able to nail down any precise cause. This seems to happen most often with ActiveStorage::PurgeJobs, but that could be just because they are common. It also happens with other Rails-specific and custom jobs alike.

Expected behavior

Jobs should be able to fetch the records they need to perform the job and continue without a problem in every case.

Actual behavior

About one job in a thousand results in this error:

undefined method `[]' for nil:NilClass
/srv/app/shared/bundle/ruby/2.5.0/gems/activerecord-5.2.0/lib/active_record/connection_adapters/abstract/connection_pool.rb:389:in `active_connection?'
/srv/app/shared/bundle/ruby/2.5.0/gems/activerecord-5.2.0/lib/active_record/connection_adapters/abstract/query_cache.rb:36:in `enable_query_cache!'
/srv/app/shared/bundle/ruby/2.5.0/gems/activerecord-5.2.0/lib/active_record/query_cache.rb:32:in `block in run'
/srv/app/shared/bundle/ruby/2.5.0/gems/activerecord-5.2.0/lib/active_record/query_cache.rb:29:in `map'
/srv/app/shared/bundle/ruby/2.5.0/gems/activerecord-5.2.0/lib/active_record/query_cache.rb:29:in `run'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/execution_wrapper.rb:27:in `before'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/callbacks.rb:426:in `block in make_lambda'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/callbacks.rb:198:in `block (2 levels) in halting'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/callbacks.rb:606:in `block (2 levels) in default_terminator'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/callbacks.rb:605:in `catch'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/callbacks.rb:605:in `block in default_terminator'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/callbacks.rb:199:in `block in halting'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/callbacks.rb:513:in `block in invoke_before'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/callbacks.rb:513:in `each'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/callbacks.rb:513:in `invoke_before'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/callbacks.rb:131:in `run_callbacks'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/execution_wrapper.rb:110:in `run!'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/execution_wrapper.rb:72:in `block in run!'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/execution_wrapper.rb:69:in `tap'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/execution_wrapper.rb:69:in `run!'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/execution_wrapper.rb:85:in `wrap'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/reloader.rb:72:in `wrap'
/srv/app/shared/bundle/ruby/2.5.0/gems/activejob-5.2.0/lib/active_job/railtie.rb:27:in `block (3 levels) in <class:Railtie>'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/callbacks.rb:118:in `instance_exec'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/callbacks.rb:118:in `block in run_callbacks'
/srv/app/shared/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/callbacks.rb:136:in `run_callbacks'
/srv/app/shared/bundle/ruby/2.5.0/gems/activejob-5.2.0/lib/active_job/execution.rb:22:in `execute'
/srv/app/shared/bundle/ruby/2.5.0/gems/activejob-5.2.0/lib/active_job/queue_adapters/resque_adapter.rb:47:in `perform'

Retrying the job manually seems to work.

System configuration

Rails version: 5.2.0

Ruby version: 2.5.1

[rafaelfranca]

Can you please provide a sample application that reproduces the error?

[eugeneius]

This looks like the same problem as #33022.

[rails-bot]

This issue has been automatically marked as stale because it has not been commented on for at least three months.
The resources of the Rails team are limited, and so we are asking for your help.
If you can still reproduce this error on the 5-2-stable branch or on master, please reply with all of the information you have about it in order to keep the issue open.
Thank you for all your contributions.