Mark a pg connection as invalid on connection err. Builds on PR #2557 by @jawj

lib/dialects/postgres/connection-manager.js

@@ -82,6 +82,11 @@ ConnectionManager.prototype.connect = function(config) {
         reject(new Error('Connection timed out'));
       }
     });
+
+    // Don't let a Postgres restart (or error) to take down the whole app
+    connection.on('error', function(err, client) {
+      connection._invalid = true;
+    });
   }).tap(function (connection) {
     if (self.sequelize.config.keepDefaultTimezone) return;
     return new Promise(function (resolve, reject) {
@@ -100,4 +105,8 @@ ConnectionManager.prototype.disconnect = function(connection) {
   });
 };
 
+ConnectionManager.prototype.validate = function(connection) {
+  return connection._invalid === undefined;
+};
+
 module.exports = ConnectionManager;