[HBASE-21969] Improve the update of destination rsgroup of RSGroupInfoManagerImpl#moveTables()

• Type: Task
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 3.0.0-alpha-1, 1.5.0, 2.3.0
• Component/s: rsgroup
• Assignee: Xiang Li
• Reporter: Xiang Li
• Created: 27/Feb/19 16:00
• Updated: 07/Apr/20 20:49
• Resolved: 01/Mar/19 06:15

Description

RSGroupInfoManagerImpl#moveTables() has the following code:

for (TableName tableName : tableNames) {
  ....
  if (groupName != null) {
    RSGroupInfo dst = new RSGroupInfo(newGroupMap.get(groupName));
    dst.addTable(tableName);
    newGroupMap.put(dst.getName(), dst);
  }
}

It is to add the tables to "dst" (the destination rsgroup) and put it back to newGroupMap to replace the old RSGroupInfo instance in the map.
The current logic allocates a new RSGroupInfo instance and calls put operation of map for each table to move, which is not needed and causes a lot of objects to be allocated (the constructor of RSGroupInfo allocates 2 TreeSets).
The logic could be improved as: allocate a new RSGroupInfo only once, add all tables, and put it into the map.