Resolve "Error 500 loading status of Geo primary node when replication lag is high"

changelogs/unreleased-ee/4773-replication-slots-max-retained-wal-bytes-too-small.yml

+---
+title: Fix 500 errors caused by large replication slot wal retention
+merge_request: 4347
+author:
+type: fixed

db/migrate/20180201101405_change_geo_node_status_column_size.rb

+class ChangeGeoNodeStatusColumnSize < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  def up
+    change_column :geo_node_statuses, :replication_slots_max_retained_wal_bytes, :integer, limit: 8
+  end
+
+  def down
+    change_column :geo_node_statuses, :replication_slots_max_retained_wal_bytes, :integer, limit: 4
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20180131104538) do
+ActiveRecord::Schema.define(version: 20180201101405) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -992,7 +992,7 @@ ActiveRecord::Schema.define(version: 20180131104538) do
     t.string "status_message"
     t.integer "replication_slots_count"
     t.integer "replication_slots_used_count"
-    t.integer "replication_slots_max_retained_wal_bytes"
+    t.integer "replication_slots_max_retained_wal_bytes", limit: 8
     t.integer "wikis_count"
     t.integer "wikis_synced_count"
     t.integer "wikis_failed_count"

spec/ee/spec/models/geo_node_status_spec.rb

@@ -379,6 +379,13 @@ describe GeoNodeStatus, :geo do
 
       expect(subject.replication_slots_max_retained_wal_bytes).to eq(2.megabytes)
     end
+
+    it 'handles large values' do
+      stub_current_geo_node(primary)
+      allow(primary).to receive(:replication_slots_max_retained_wal_bytes).and_return(900.gigabytes)
+
+      expect(subject.replication_slots_max_retained_wal_bytes).to eq(900.gigabytes)
+    end
   end
 
   describe '#last_event_id and #last_event_date' do