Set up Delayed Job as the backend for Active Job

This persists jobs into the database, and uses locking to ensure that
workers from multiple machines avoid treading on each other.

Jobs can be run by using `bundle exec rake jobs:work`

Fixes #2015

Gemfile

@@ -46,6 +46,7 @@ gem "image_optim_rails"
 # Load rails plugins
 gem "actionpack-page_caching"
 gem "composite_primary_keys", "~> 11.0.0"
+gem "delayed_job_active_record"
 gem "dynamic_form"
 gem "http_accept_language", "~> 2.0.0"
 gem "i18n-js", ">= 3.0.0"

Gemfile.lock

@@ -99,6 +99,11 @@ GEM
     crass (1.0.4)
     dalli (2.7.8)
     debug_inspector (0.0.3)
+    delayed_job (4.1.5)
+      activesupport (>= 3.0, < 5.3)
+    delayed_job_active_record (4.1.3)
+      activerecord (>= 3.0, < 5.3)
+      delayed_job (>= 3.0, < 5)
     docile (1.3.1)
     dynamic_form (1.1.4)
     erubi (1.7.1)
@@ -393,6 +398,7 @@ DEPENDENCIES
   composite_primary_keys (~> 11.0.0)
   coveralls
   dalli
+  delayed_job_active_record
   dynamic_form
   factory_bot_rails
   faraday

config/application.rb

@@ -51,5 +51,8 @@ module OpenStreetMap
       config.logstasher.logger_path = LOGSTASH_PATH
       config.logstasher.log_controller_parameters = true
     end
+
+    # Use DelayedJob as the persistent backend for ActiveJob
+    config.active_job.queue_adapter = :delayed_job
   end
 end

db/migrate/20181031113522_create_delayed_jobs.rb

@@ -0,0 +1,22 @@
+class CreateDelayedJobs < ActiveRecord::Migration[5.2]
+  def self.up
+    create_table :delayed_jobs, :force => true do |table|
+      table.integer :priority, :default => 0, :null => false # Allows some jobs to jump to the front of the queue
+      table.integer :attempts, :default => 0, :null => false # Provides for retries, but still fail eventually.
+      table.text :handler,                    :null => false # YAML-encoded string of the object that will do work
+      table.text :last_error                                 # reason for last failure (See Note below)
+      table.datetime :run_at                                 # When to run. Could be Time.zone.now for immediately, or sometime in the future.
+      table.datetime :locked_at                              # Set when a client is working on this object
+      table.datetime :failed_at                              # Set when all retries have failed (actually, by default, the record is deleted instead)
+      table.string :locked_by                                # Who is working on this object (if locked)
+      table.string :queue                                    # The name of the queue this job is in
+      table.timestamps :null => true
+    end
+
+    add_index :delayed_jobs, [:priority, :run_at], :name => "delayed_jobs_priority"
+  end
+
+  def self.down
+    drop_table :delayed_jobs
+  end
+end

db/structure.sql

@@ -494,6 +494,45 @@ CREATE SEQUENCE current_ways_id_seq
 ALTER SEQUENCE current_ways_id_seq OWNED BY current_ways.id;
 
 
+--
+-- Name: delayed_jobs; Type: TABLE; Schema: public; Owner: -
+--
+
+CREATE TABLE delayed_jobs (
+    id bigint NOT NULL,
+    priority integer DEFAULT 0 NOT NULL,
+    attempts integer DEFAULT 0 NOT NULL,
+    handler text NOT NULL,
+    last_error text,
+    run_at timestamp without time zone,
+    locked_at timestamp without time zone,
+    failed_at timestamp without time zone,
+    locked_by character varying,
+    queue character varying,
+    created_at timestamp without time zone,
+    updated_at timestamp without time zone
+);
+
+
+--
+-- Name: delayed_jobs_id_seq; Type: SEQUENCE; Schema: public; Owner: -
+--
+
+CREATE SEQUENCE delayed_jobs_id_seq
+    START WITH 1
+    INCREMENT BY 1
+    NO MINVALUE
+    NO MAXVALUE
+    CACHE 1;
+
+
+--
+-- Name: delayed_jobs_id_seq; Type: SEQUENCE OWNED BY; Schema: public; Owner: -
+--
+
+ALTER SEQUENCE delayed_jobs_id_seq OWNED BY delayed_jobs.id;
+
+
 --
 -- Name: diary_comments; Type: TABLE; Schema: public; Owner: -
 --
@@ -1365,6 +1404,13 @@ ALTER TABLE ONLY current_relations ALTER COLUMN id SET DEFAULT nextval('current_
 ALTER TABLE ONLY current_ways ALTER COLUMN id SET DEFAULT nextval('current_ways_id_seq'::regclass);
 
 
+--
+-- Name: delayed_jobs id; Type: DEFAULT; Schema: public; Owner: -
+--
+
+ALTER TABLE ONLY delayed_jobs ALTER COLUMN id SET DEFAULT nextval('delayed_jobs_id_seq'::regclass);
+
+
 --
 -- Name: diary_comments id; Type: DEFAULT; Schema: public; Owner: -
 --
@@ -1595,6 +1641,14 @@ ALTER TABLE ONLY current_ways
     ADD CONSTRAINT current_ways_pkey PRIMARY KEY (id);
 
 
+--
+-- Name: delayed_jobs delayed_jobs_pkey; Type: CONSTRAINT; Schema: public; Owner: -
+--
+
+ALTER TABLE ONLY delayed_jobs
+    ADD CONSTRAINT delayed_jobs_pkey PRIMARY KEY (id);
+
+
 --
 -- Name: diary_comments diary_comments_pkey; Type: CONSTRAINT; Schema: public; Owner: -
 --
@@ -1918,6 +1972,13 @@ CREATE INDEX current_way_nodes_node_idx ON current_way_nodes USING btree (node_i
 CREATE INDEX current_ways_timestamp_idx ON current_ways USING btree ("timestamp");
 
 
+--
+-- Name: delayed_jobs_priority; Type: INDEX; Schema: public; Owner: -
+--
+
+CREATE INDEX delayed_jobs_priority ON delayed_jobs USING btree (priority, run_at);
+
+
 --
 -- Name: diary_comment_user_id_created_at_index; Type: INDEX; Schema: public; Owner: -
 --
@@ -2870,6 +2931,7 @@ INSERT INTO "schema_migrations" (version) VALUES
 ('20161011010929'),
 ('20170222134109'),
 ('20180204153242'),
+('20181031113522'),
 ('21'),
 ('22'),
 ('23'),