ROOT region appeared in two regionserver's onlineRegions at the same time
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Key: HBASE-3914
URL: https://issues.apache.org/jira/browse/HBASE-3914
Project: HBase
Issue Type: Bug
Components: master
Affects Versions: 0.90.3
Reporter: Jieshan Bean
Fix For: 0.90.4
This could be happen under the following steps with little probability:
(I suppose the cluster nodes names are RS1/RS2/HM, and there's more than 10,000
regions in the cluster)
1.Root region was opened in RS1.
2.Due to some reason(Maybe the hdfs process was got abnormal),RS1 aborted.
3.ServerShutdownHandler process start.
4.HMaster was restarted, during the finishInitialization's handling, ROOT
region was unsetted, and assigned to RS2.
5.Root region was opened successfully in RS2.
6.But after while, ROOT region was unsetted again by RS1's
ServerShutdownHandler. Then it was reassigned. Before that, the RS1 was
restarted. So there's two possibilities:
Case a:
ROOT region was assigned to RS1.
It seemed nothing would be affected. But the root region was still online in
RS2.
Case b:
ROOT region was assigned to RS2.
The ROOT Region couldn't be opened until it would be reassigned to other
regionserver, because it was showed online in this regionserver.
This could be proved from the logs:
1. ROOT region was opened with two times:
2011-05-17 10:32:59,188 DEBUG
org.apache.hadoop.hbase.master.handler.OpenedRegionHandler: Opened region
-ROOT-,,0.70236052 on 162-2-77-0,20020,1305598359031
2011-05-17 10:33:01,536 DEBUG
org.apache.hadoop.hbase.master.handler.OpenedRegionHandler: Opened region
-ROOT-,,0.70236052 on 162-2-16-6,20020,1305597548212
2.Regionserver 162-2-16-6 was aborted, so it was reassigned to 162-2-77-0, but
already online on this server:
10:49:30,920 INFO org.apache.hadoop.hbase.regionserver.HRegionServer: Received
request to open region: -ROOT-,,0.70236052 10:49:30,920 DEBUG
org.apache.hadoop.hbase.regionserver.handler.OpenRegionHandler: Processing open
of -ROOT-,,0.70236052 10:49:30,920 WARN
org.apache.hadoop.hbase.regionserver.handler.OpenRegionHandler: Attempted open
of -ROOT-,,0.70236052 but already online on this server
This could be cause a long break of ROOT region offline, though it happened
under a special scenario. And I have checked the code, it seems a tiny bug here.
There's 2 references about assignRoot():
1.
HMaster# assignRootAndMeta:
if (!catalogTracker.verifyRootRegionLocation(timeout)) {
this.assignmentManager.assignRoot();
this.catalogTracker.waitForRoot();
assigned++;
}
2.
ServerShutdownHandler# process:
if (isCarryingRoot()) { // -ROOT-
try {
this.services.getAssignmentManager().assignRoot();
} catch (KeeperException e) {
this.server.abort("In server shutdown processing, assigning root",
e);
throw new IOException("Aborting", e);
}
}
I think each time call the method of assignRoot(), we should verify Root
Region's Location first. Because before the assigning, the ROOT region could
have been assigned by another place.
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