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Ted Yu commented on HBASE-18628: -------------------------------- Please attach one of the stack traces you collected to this JIRA. > ZKPermissionWatcher blocks all ZK notifications > ----------------------------------------------- > > Key: HBASE-18628 > URL: https://issues.apache.org/jira/browse/HBASE-18628 > Project: HBase > Issue Type: Bug > Components: regionserver > Reporter: Mike Drob > Priority: Critical > > Buckle up folks, we're going for a ride here. I've seeing this on a branch-2 > based build, but I think the problem will affect branch-1 as well. I'm not > able to easily reproduce the issue, but it will usually come up within an > hour on a given cluster that I have, at which point the problem persists > until an RS restart. I've been seeing the problem and paying attention for > maybe two months, but I suspect it's been happening much longer than that. > h3. Problem > When running in a secure cluster, sometimes the ZK EventThread will get stuck > on a permissions update and not be able to process new notifications. This > happens to also block flush and snapshot, which is how we found it. > h3. Analysis > The main smoking gun is seeing this in repeated jstacks: > {noformat} > "main-EventThread" #43 daemon prio=5 os_prio=0 tid=0x00007f0b92644000 > nid=0x6e69 waiting on condition [0x00007f0b6730f000] > java.lang.Thread.State: TIMED_WAITING (sleeping) > at java.lang.Thread.sleep(Native Method) > at > org.apache.hadoop.hbase.security.access.ZKPermissionWatcher.nodeChildrenChanged(ZKPermissionWatcher.java:191) > at > org.apache.hadoop.hbase.zookeeper.ZooKeeperWatcher.process(ZooKeeperWatcher.java:503) > at > org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:522) > at > org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:498) > {noformat} > That sleep is a 20ms sleep in an {{AtomicReference.compareAndSet}} loop - but > it never gets past the condition. > {code} > while (!nodes.compareAndSet(null, nodeList)) { > try { > Thread.sleep(20); > } catch (InterruptedException e) { > LOG.warn("Interrupted while setting node list", e); > Thread.currentThread().interrupt(); > } > } > {code} > The warning never shows up in the logs, it just keeps looping and looping. > The last relevant line from the watcher in logs is: > {noformat} > 2017-08-17 21:25:12,379 DEBUG > org.apache.hadoop.hbase.zookeeper.ZooKeeperWatcher: > regionserver:22101-0x15df38884c80024, quorum=zk1:2181,zk2:2181,zk3:2181, > baseZNode=/hbase Received ZooKeeper Event, type=NodeChildrenChanged, > state=SyncConnected, path=/hbase/acl > {noformat} > Which makes sense, because the code snippet is from permission watcher's > {{nodeChildrenChanged}} handler. > The separate thread introduced in HBASE-14370 is present, but not doing > anything. And this event hasn't gotten to the part where it splits off into a > thread: > {noformat} > "zk-permission-watcher4-thread-1" #160 daemon prio=5 os_prio=0 > tid=0x0000000001750800 nid=0x6fd9 waiting on condition [0x00007f0b5dce5000] > java.lang.Thread.State: WAITING (parking) > at sun.misc.Unsafe.park(Native Method) > - parking to wait for <0x00000007436ecea0> (a > java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject) > at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175) > at > java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039) > at > java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442) > at > java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074) > at > java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134) > at > java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) > at java.lang.Thread.run(Thread.java:748) > {noformat} > h3. Solutions > There's a few approaches we can take to fix this, I think they are all > complimentary. It might be useful to file subtasks or new issues for some of > the solutions if they are longer term. > # Move flush and snapshot to ProcedureV2. This makes my proximate problem go > away, but it's only relevant to branch-2 and master, and doesn't fix anything > on branch-1. Also, Permissions updates would still get stuck, preventing > future permissions updates. I think this is important long term for the > robustness of the system, but not a viable short term fix. > # Add an Executor to ZookeeperWatcher and launch threads from there. Maybe > we'd want to pull the Executor out of ZKPW, but that's not strictly necessary > and can be optimized later -- if we're already threading, then adding another > layer isn't a huge cost. > # Figure out the race condition or logic problem that causes {{nodes}} to be > non-null above. I've tried looking at this and visual inspection isn't > getting me anywhere. -- This message was sent by Atlassian JIRA (v6.4.14#64029)