[HBASE-3668] CatalogTracker.waitForMeta can wait forever and totally stall a RS

• Type: Bug
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 0.90.1
• Fix Version/s: 0.90.2
• Hadoop Flags: Reviewed
• Assignee: Jean-Daniel Cryans
• Reporter: Jean-Daniel Cryans
• Created: 17/Mar/11 21:57
• Updated: 20/Nov/15 12:44
• Resolved: 22/Mar/11 23:52

Description

We got into a weird situation after hitting HBASE-3664 leaving almost half the region servers unable to open regions (we didn't kill the master but all RS were restarted).

Here's the relevant jstack from the region servers:

"regionserver60020-EventThread" daemon prio=10 tid=0x0000000041297800 nid=0x5c5 in Object.wait() [0x00007fbd2b7f6000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
	at java.lang.Object.wait(Native Method)
	- waiting on <0x00007fbd4e1ac6d0> (a java.util.concurrent.atomic.AtomicBoolean)
	at org.apache.hadoop.hbase.catalog.CatalogTracker.waitForMeta(CatalogTracker.java:328)
	- locked <0x00007fbd4e1ac6d0> (a java.util.concurrent.atomic.AtomicBoolean)
	at org.apache.hadoop.hbase.catalog.CatalogTracker.waitForMetaServerConnectionDefault(CatalogTracker.java:363)
	at org.apache.hadoop.hbase.zookeeper.MetaNodeTracker.nodeDeleted(MetaNodeTracker.java:64)
	at org.apache.hadoop.hbase.zookeeper.ZooKeeperNodeTracker.nodeCreated(ZooKeeperNodeTracker.java:154)
	- locked <0x00007fbd4d7ab060> (a org.apache.hadoop.hbase.zookeeper.MetaNodeTracker)
	at org.apache.hadoop.hbase.zookeeper.ZooKeeperNodeTracker.nodeDataChanged(ZooKeeperNodeTracker.java:179)
	- locked <0x00007fbd4d7ab060> (a org.apache.hadoop.hbase.zookeeper.MetaNodeTracker)
	at org.apache.hadoop.hbase.zookeeper.ZooKeeperWatcher.process(ZooKeeperWatcher.java:268)
	at org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:530)
	at org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:506)

Every server in that state cannot receive any ZK event. See how we first do a nodeDataChanged, then nodeCreated, then nodeDeleted. This is correlated in the logs:

2011-03-17 17:57:03,636 DEBUG org.apache.hadoop.hbase.zookeeper.ZooKeeperWatcher: regionserver:60020-0x12d627b723e081f Received ZooKeeper Event, type=NodeDataChanged, state=SyncConnected, path=/hbase/unassigned/1028785192
2011-03-17 17:57:03,636 DEBUG org.apache.hadoop.hbase.zookeeper.ZKUtil: regionserver:60020-0x12d627b723e081f Unable to get data of znode /hbase/unassigned/1028785192 because node does not exist (not an error)
2011-03-17 17:57:03,637 DEBUG org.apache.hadoop.hbase.zookeeper.ZKUtil: regionserver:60020-0x12d627b723e081f Set watcher on existing znode /hbase/unassigned/1028785192
2011-03-17 17:57:03,637 INFO org.apache.hadoop.hbase.zookeeper.MetaNodeTracker: Detected completed assignment of META, notifying catalog tracker
2011-03-17 17:57:06,988 DEBUG org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation: Lookedup root region location, connection=org.

Node is updated, then is missing, than came back! The reason we're stuck is that CT.waitForMeta will wait forever:

     if (getMetaServerConnection(true) != null) {
        return metaLocation;
      }
      while(!stopped && !metaAvailable.get() &&
          (timeout == 0 || System.currentTimeMillis() < stop)) {
        metaAvailable.wait(timeout);
      }

So when it tried getMetaServerConnection the first time it didn't work, and then since the timeout is 0 then it waits. Even if it was looping, metaAvailable will never be true since we're already inside the event thread thus blocking any other event!

This is what happens when the RS then tries to update .META. after opening a region:

2011-03-17 17:59:06,557 DEBUG org.apache.hadoop.hbase.regionserver.handler.OpenRegionHandler: Interrupting thread Thread[PostOpenDeployTasks:f06b630822a161d0a8fe37481d851d05,5,main]
2011-03-17 17:59:06,557 WARN org.apache.hadoop.hbase.regionserver.handler.OpenRegionHandler: Exception running postOpenDeployTasks; region=f06b630822a161d0a8fe37481d851d05
org.apache.hadoop.hbase.NotAllMetaRegionsOnlineException: Interrupted
        at org.apache.hadoop.hbase.catalog.CatalogTracker.waitForMetaServerConnectionDefault(CatalogTracker.java:365)
        at org.apache.hadoop.hbase.catalog.MetaEditor.updateRegionLocation(MetaEditor.java:142)
        at org.apache.hadoop.hbase.regionserver.HRegionServer.postOpenDeployTasks(HRegionServer.java:1359)

The master eventually tries to assign the region somewhere else where it may work, but then the balancer will screw everything up again.