Create and schedule job to delete old alert runs

Daily job to delete any Subscription Alert Run created longer than 7
days ago.

We only need the alert runs to check if the alert was already triggered
for the current date.
At the moment, the table contains 16M records for over 100k
subscriptions.
We do not need that data at all.

Reducing it to only keeping the latest week will greatly reduce the
table size without compromising the recent runs check.

app/jobs/delete_old_alert_runs_job.rb

@@ -0,0 +1,7 @@
+class DeleteOldAlertRunsJob < ApplicationJob
+  queue_as :low
+
+  def perform
+    AlertRun.where(run_on: ...1.week.ago).destroy_all
+  end
+end

config/schedule.yml

@@ -82,6 +82,11 @@ delete_old_applications:
   class: 'DeleteOldNonDraftJobApplicationsJob'
   queue: low
 
+delete_old_alert_runs:
+  cron: '10 5 * * *' # "At 05:10."
+  class: 'DeleteOldAlertRunsJob'
+  queue: low
+
 refresh_markers:
   cron: '0 6 * * *' # "At 06:00."
   class: 'RefreshMarkersJob'

spec/jobs/delete_old_alert_runs_job_spec.rb

@@ -0,0 +1,21 @@
+require "rails_helper"
+
+RSpec.describe DeleteOldAlertRunsJob do
+  it "deletes alert runs older than a week" do
+    alert_run = create(:alert_run, run_on: 8.days.ago)
+    described_class.perform_now
+    expect(AlertRun).not_to exist(alert_run.id)
+  end
+
+  it "does not delete alert runs from exactly a week ago" do
+    alert_run = create(:alert_run, run_on: 7.days.ago)
+    described_class.perform_now
+    expect(AlertRun).to exist(alert_run.id)
+  end
+
+  it "does not delete alert runs newer than a week" do
+    alert_run = create(:alert_run, run_on: 6.days.ago)
+    described_class.perform_now
+    expect(AlertRun).to exist(alert_run.id)
+  end
+end