[HBASE-3946] The splitted region can be online again while the standby hmaster becomes the active one

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.90.3
• Fix Version/s: 0.90.4
• Hadoop Flags: Reviewed
• Assignee: Jieshan Bean
• Reporter: Jieshan Bean
• Created: 02/Jun/11 00:55
• Updated: 20/Nov/15 12:42
• Resolved: 08/Jun/11 16:38

Description

(The cluster has two HMatser, one active and one standby)

1.While the active HMaster shutdown, the standby one would become the active one, and went into the processFailover() method:
if (regionCount == 0)

{ LOG.info("Master startup proceeding: cluster startup"); this.assignmentManager.cleanoutUnassigned(); this.assignmentManager.assignAllUserRegions(); }

else

{ LOG.info("Master startup proceeding: master failover"); this.assignmentManager.processFailover(); }

2.After that, the user regions would be rebuild.
Map<HServerInfo,List<Pair<HRegionInfo,Result>>> deadServers = rebuildUserRegions();

3.Here's how the rebuildUserRegions worked. All the regions(contain the splitted regions) would be added to the offlineRegions of offlineServers.

for (Result result : results) {
Pair<HRegionInfo,HServerInfo> region =
MetaReader.metaRowToRegionPairWithInfo(result);
if (region == null) continue;
HServerInfo regionLocation = region.getSecond();
HRegionInfo regionInfo = region.getFirst();
if (regionLocation == null)

{ // Region not being served, add to region map with no assignment // If this needs to be assigned out, it will also be in ZK as RIT this.regions.put(regionInfo, null); }

else if (!serverManager.isServerOnline(
regionLocation.getServerName())) {
// Region is located on a server that isn't online
List<Pair<HRegionInfo,Result>> offlineRegions =
offlineServers.get(regionLocation);
if (offlineRegions == null)

{ offlineRegions = new ArrayList<Pair<HRegionInfo,Result>>(1); offlineServers.put(regionLocation, offlineRegions); }

offlineRegions.add(new Pair<HRegionInfo,Result>(regionInfo, result));
} else

{ // Region is being served and on an active server regions.put(regionInfo, regionLocation); addToServers(regionLocation, regionInfo); }

}

4.It seems that all the offline regions will be added to RIT and online again:
ZKAssign will creat node for each offline never consider the splitted ones.

AssignmentManager# processDeadServers
private void processDeadServers(
Map<HServerInfo, List<Pair<HRegionInfo, Result>>> deadServers)
throws IOException, KeeperException {
for (Map.Entry<HServerInfo, List<Pair<HRegionInfo,Result>>> deadServer :
deadServers.entrySet()) {
List<Pair<HRegionInfo,Result>> regions = deadServer.getValue();
for (Pair<HRegionInfo,Result> region : regions) {
HRegionInfo regionInfo = region.getFirst();
Result result = region.getSecond();
// If region was in transition (was in zk) force it offline for reassign
try

{ ZKAssign.createOrForceNodeOffline(watcher, regionInfo, master.getServerName()); }

catch (KeeperException.NoNodeException nne)

{ // This is fine }

// Process with existing RS shutdown code
ServerShutdownHandler.processDeadRegion(regionInfo, result, this,
this.catalogTracker);
}
}
}

AssignmentManager# processFailover
// Process list of dead servers
processDeadServers(deadServers);
// Check existing regions in transition
List<String> nodes = ZKUtil.listChildrenAndWatchForNewChildren(watcher,
watcher.assignmentZNode);
if (nodes.isEmpty())

{ LOG.info("No regions in transition in ZK to process on failover"); return; }

LOG.info("Failed-over master needs to process " + nodes.size() +
" regions in transition");
for (String encodedRegionName: nodes)

{ processRegionInTransition(encodedRegionName, null); }

So I think before add the region into RIT, check it at first.