[HBASE-21987] Simplify RSGroupInfoManagerImpl#flushConfig() for offline mode

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 3.0.0-alpha-1, 1.5.0, 2.2.0
• Component/s: rsgroup
• Labels: rsgroup
• Assignee: Xiang Li
• Reporter: Xiang Li
• Created: 04/Mar/19 17:14
• Updated: 28/Apr/19 00:56
• Resolved: 11/Mar/19 21:13

Description

The logic to handle offline mode in RSGroupInfoManagerImpl#flushConfig(Map<String, RSGroupInfo> newGroupMap) could be simplified.

RSGroupInfoManagerImpl.java # flushConfig(Map<String, RSGroupInfo> newGroupMap)

if (!isOnline()) {
    Map<String, RSGroupInfo> m = Maps.newHashMap(rsGroupMap);
    RSGroupInfo oldDefaultGroup = m.remove(RSGroupInfo.DEFAULT_GROUP);
    RSGroupInfo newDefaultGroup = newGroupMap.remove(RSGroupInfo.DEFAULT_GROUP);
    if (!m.equals(newGroupMap) ||
        !oldDefaultGroup.getTables().equals(newDefaultGroup.getTables())) {
        throw new IOException("Only default servers can be updated during offline mode");
    }
    newGroupMap.put(RSGroupInfo.DEFAULT_GROUP, newDefaultGroup);
    rsGroupMap = newGroupMap;
    return;
 }

The logic is to make a copy of the private member called "rsGroupMap" as m, and get the default group out of m and newGroupMap and then compare. Then restore the newGroupMap and update rsGroupMap.
This function is called by

RSGroupInfoManagerImpl.java # flushConfig()

private synchronized void flushConfig() throws IOException {
    flushConfig(this.rsGroupMap);
}

by RSGroupInfoManagerImpl.RSGroupStartupWorker#waitForGroupTableOnline() during HMaster starts, in which, newGroupMap (the input of flushConfig()) is this.rsGroupMap, the comparison is not needed, because they are the same.