Improve the query performance to find unsynced job artifacts

ee/app/finders/geo/job_artifact_registry_finder.rb

@@ -141,7 +141,7 @@ module Geo
       fdw_job_artifacts.joins("LEFT OUTER JOIN job_artifact_registry
                                ON job_artifact_registry.artifact_id = #{fdw_job_artifacts_table}.id")
         .with_files_stored_locally
-        .where(job_artifact_registry: { id: nil })
+        .where(job_artifact_registry: { artifact_id: nil })
         .where.not(id: except_artifact_ids)
     end
 

ee/db/geo/migrate/20180412213305_add_index_to_artifact_id_on_job_artifact_registry.rb

+class AddIndexToArtifactIdOnJobArtifactRegistry < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :job_artifact_registry, :artifact_id
+  end
+
+  def down
+    if index_exists?(:job_artifact_registry, :artifact_id)
+      remove_concurrent_index :job_artifact_registry_finder, :artifact_id
+    end
+  end
+end

ee/db/geo/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20180405074130) do
+ActiveRecord::Schema.define(version: 20180412213305) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -47,6 +47,7 @@ ActiveRecord::Schema.define(version: 20180405074130) do
     t.boolean "missing_on_primary", default: false, null: false
   end
 
+  add_index "job_artifact_registry", ["artifact_id"], name: "index_job_artifact_registry_on_artifact_id", using: :btree
   add_index "job_artifact_registry", ["retry_at"], name: "index_job_artifact_registry_on_retry_at", using: :btree
   add_index "job_artifact_registry", ["success"], name: "index_job_artifact_registry_on_success", using: :btree