[HBASE-7340] Master coprocessor notification for assignmentManager.balance() is inconsistent

• Type: Improvement
• Status: Closed
• Priority: Trivial
• Resolution: Fixed
• Fix Version/s: 0.95.0
• Hadoop Flags: Reviewed
• Assignee: Ted Yu
• Reporter: Ted Yu
• Created: 12/Dec/12 20:34
• Updated: 23/Sep/13 18:45
• Resolved: 13/Dec/12 21:12

Description

I found this issue when reading user discussion which is quoted below.

In HMaster.moveRegion(), we have:

      this.assignmentManager.balance(rp);
      if (this.cpHost != null) {
        this.cpHost.postMove(hri, rp.getSource(), rp.getDestination());
      }

Meaning, user can register master coprocessor which would receive region movement notification.

The assignmentManager.balance(plan) call in HMaster.balance() doesn't send out such notification.
I think we should enhance the following hook (at line 1335) with list of regions moved so that notification from master is consistent:

        this.cpHost.postBalance();

Here is excerpt for user discussion:

Sometimes user performs compaction after a region is moved (by balancer). We should provide 'hook' which lets user specify what follow-on actions to take after region movement.

See discussion on user mailing list under the thread 'How to know it's time for a major compaction?' for background information: http://search-hadoop.com/m/BDx4S1jMjF92&subj=How+to+know+it+s+time+for+a+major+compaction+