Fix future iterations not being scheduled

What does this MR do and why?

Resolves #365741 (closed).

An iterations cadence, cadence for short, contains many iterations (one-to-many.) Iterations for a cadence are scheduled and created automatically without user intervention by workers like this:

1. Iterations::Cadences::ScheduleCreateIterationsWorker batches through cadences. The worker picks up cadences using the scope Iterations::Cadence.for_automated_iterations

2. For each cadence, Iterations::Cadences::CreateIterationsWorker is executed.

Unfortunately, the scope :for_automated_iterations is incorrect and iterations are not being correctly created. In this MR, we are

1. fixing the scope

2. and running a data migration so that Iterations::Cadences::ScheduleCreateIterationsWorker can pick up all the cadences whose iterations have not been scheduled correctly.

How to set up and validate locally

The attribute last_run_date cannot be manually set and the validation steps are somewhat more involved.

1. Ensure that :iterations_cadences is enabled (the FF is enabled by default.)

   Feature.enable(:iterations_cadences)

2. Temporarily comment out the following line so that the worker isn't run when a new cadence record is created:

Comment out ee/app/models/iterations/cadence.rb#77

    def ensure_iterations_in_advance
-     ::Iterations::Cadences::CreateIterationsWorker.perform_async(self.id) if self.can_be_automated?
+      # ::Iterations::Cadences::CreateIterationsWorker.perform_async(self.id) if self.can_be_automated?
    end

1. Create a new cadence whose last_run_date is in the past.

This cadence should be picked up by 'ScheduleCreateIterationsWorker' because it uses the updated scope Iterations::Cadence.next_to_auto_schedule. The cadence wouldn't have been picked up with the old scope Iterations::Cadence.for_automated_iterations.

common_args = { 
  group: Group.last, # Use your preferred group
  start_date: Date.today,
  title: "Sample Cadence",
  duration_in_weeks: 1,
  iterations_in_advance: 2,
}
cadence_a = Iterations::Cadence.create(**common_args, last_run_date: Date.today - 5.days)

1. Create a new cadence whose last_run_date is in the future.

cadence_b = Iterations::Cadence.create(**common_args, last_run_date: Date.today + 5.days)

1. Run the worker Iterations::Cadences::ScheduleCreateIterationsWorker in the rails console (this may take some minutes. Please check the application log.)

Iterations::Cadences::ScheduleCreateIterationsWorker.perform_in(1.second)

1. Verify that only cadence_a has iteration records associated.

cadence_a.reload.iterations.size # expected 2
cadence_b.reload.iterations.size # expected 0

Database Review

The query plan for the post migration: !90620 (comment 998516410).

The post migration is a data migration and would update ~1k records in production (~100 in staging)

Query plan (cold cache/dblab):

gitlabhq_dblab=# explain (analyze, buffers) UPDATE iterations_cadences SET last_run_date=CURRENT_DATE WHERE automatic=true;
                                                        QUERY PLAN                                                         
---------------------------------------------------------------------------------------------------------------------------
 Update on iterations_cadences  (cost=0.00..336.77 rows=989 width=88) (actual time=260.461..260.462 rows=0 loops=1)
   Buffers: shared hit=10042 read=177 dirtied=184 written=17
   I/O Timings: read=208.046
   ->  Seq Scan on iterations_cadences  (cost=0.00..336.77 rows=989 width=88) (actual time=2.626..78.901 rows=998 loops=1)
         Filter: automatic
         Rows Removed by Filter: 3636
         Buffers: shared hit=33 read=39 dirtied=8
         I/O Timings: read=61.299
 Planning Time: 46.058 ms
 Execution Time: 261.324 ms
(10 rows)

The query plan for the modified scope Iterations:Cadence.next_to_auto_schedule: !90620 (comment 998538261)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.