Add cleanup migration for JobWaiter Redis keys

changelogs/unreleased/jv-cleanup-job-waiter.yml

+---
+title: Add cleanup migration for JobWaiter Redis keys
+merge_request: 43882
+author:
+type: fixed

db/post_migrate/20200930144340_set_job_waiter_ttl.rb

+# frozen_string_literal: true
+
+class SetJobWaiterTtl < ActiveRecord::Migration[6.0]
+  DOWNTIME = false
+
+  SCRIPT = <<~LUA.freeze
+    if redis.call("ttl", KEYS[1]) < 0 then
+      redis.call("expire", KEYS[1], 21600)
+    end
+  LUA
+
+  def up
+    Gitlab::Redis::SharedState.with do |redis|
+      cursor_init = '0'
+      cursor = cursor_init
+
+      loop do
+        cursor, keys = redis.scan(cursor, match: 'gitlab:job_waiter:*')
+
+        redis.pipelined do |redis|
+          keys.each { |k| redis.eval(SCRIPT, keys: [k]) }
+        end
+
+        break if cursor == cursor_init
+      end
+    end
+  end
+
+  def down
+  end
+end

db/schema_migrations/20200930144340

+febc66dbb48fbd281223ab9466cc5d94e945e8164fa9db0ee149c29e653b3eb2
\ No newline at end of file

spec/migrations/set_job_waiter_ttl_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20200930144340_set_job_waiter_ttl.rb')
+
+RSpec.describe SetJobWaiterTtl, :redis do
+  it 'sets TTLs where necessary' do
+    waiter_with_ttl = Gitlab::JobWaiter.new.key
+    waiter_without_ttl = Gitlab::JobWaiter.new.key
+    key_with_ttl = "foo:bar"
+    key_without_ttl = "foo:qux"
+
+    Gitlab::Redis::SharedState.with do |redis|
+      redis.set(waiter_with_ttl, "zzz", ex: 2000)
+      redis.set(waiter_without_ttl, "zzz")
+      redis.set(key_with_ttl, "zzz", ex: 2000)
+      redis.set(key_without_ttl, "zzz")
+
+      described_class.new.up
+
+      # This is the point of the migration. We know the migration uses a TTL of 21_600
+      expect(redis.ttl(waiter_without_ttl)).to be > 20_000
+
+      # Other TTL's should be untouched by the migration
+      expect(redis.ttl(waiter_with_ttl)).to be_between(1000, 2000)
+      expect(redis.ttl(key_with_ttl)).to be_between(1000, 2000)
+      expect(redis.ttl(key_without_ttl)).to eq(-1)
+    end
+  end
+end