[ACCUMULO-4557] Instance API should state when returning null is expected.

• Type: Bug
• Status: Resolved
• Priority: Critical
• Resolution: Not A Problem
• Affects Version/s: 1.7.1, 1.7.2, 1.8.0
• Component/s: client
• Assignee: Unassigned
• Reporter: Sean Busbey
• Created: 05/Jan/17 11:29
• Updated: 19/Mar/18 18:26
• Resolved: 19/Mar/18 18:26

Description

This is an issue at least in 1.6.0+. Ran into during ACCUMULO-4556.

In that case the TablesServlet is making use of Instance to get root tablet location information via the Instance interface. The API for getRootTablet in master is:

  /**
   * Returns the location of the tablet server that is serving the root tablet.
   *
   * @return location in "hostname:port" form
   */
  String getRootTabletLocation();

When the root tablet is offline, all of our current implementations return null. The data structure used in TablesServlet can't handle nulls, so the code fails with an NPE.

We should review the current implementations for Instance and update the API to include details on the circumstances where a null will be returned from all of the defined methods.