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From "zhihai xu (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (YARN-3242) Old ZK client session watcher event messed up new ZK client session due to ZooKeeper asynchronously closing client session.
Date Sun, 22 Feb 2015 17:37:11 GMT

     [ https://issues.apache.org/jira/browse/YARN-3242?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

zhihai xu updated YARN-3242:
----------------------------
    Description: 
Old ZK client session watcher event messed up new ZK client session due to ZooKeeper asynchronously
closing client session.
The watcher event from old ZK client session can still be sent to ZKRMStateStore after the
old  ZK client session is closed.
This will cause seriously problem:ZKRMStateStore out of sync with ZooKeeper session.
We only have one ZKRMStateStore but we can have multiple ZK client sessions.
Currently ZKRMStateStore#processWatchEvent doesn't check whether this watcher event is from
current session. So the watcher event from old ZK client session which just is closed will
still be processed.
For example, If a Disconnected event received from old session after new session is connected,
the zkClient will be set to null
{code}
        case Disconnected:
          LOG.info("ZKRMStateStore Session disconnected");
          oldZkClient = zkClient;
          zkClient = null;
          break;
{code}
Then ZKRMStateStore won't receive SyncConnected event from new session because new session
is already in SyncConnected state and it won't send SyncConnected event until it is disconnected
and connected again.
Then we will see all the ZKRMStateStore operations fail with IOException "Wait for ZKClient
creation timed out" until  RM shutdown.

The following code from zookeeper(ClientCnxn#EventThread) show even after receive eventOfDeath,
EventThread will still process all the events until  waitingEvents queue is empty.
{code}
              while (true) {
                 Object event = waitingEvents.take();
                 if (event == eventOfDeath) {
                    wasKilled = true;
                 } else {
                    processEvent(event);
                 }
                 if (wasKilled)
                    synchronized (waitingEvents) {
                       if (waitingEvents.isEmpty()) {
                          isRunning = false;
                          break;
                       }
                    }
              }

      private void processEvent(Object event) {
          try {
              if (event instanceof WatcherSetEventPair) {
                  // each watcher will process the event
                  WatcherSetEventPair pair = (WatcherSetEventPair) event;
                  for (Watcher watcher : pair.watchers) {
                      try {
                          watcher.process(pair.event);
                      } catch (Throwable t) {
                          LOG.error("Error while calling watcher ", t);
                      }
                  }
              } else {
{code}

  was:
Old ZK client session watcher event messed up new ZK client session due to ZooKeeper asynchronously
closing client session.
The watcher event from old ZK client session can still be sent to ZKRMStateStore after the
old  ZK client session is closed.
This will cause seriously problem:ZKRMStateStore out of sync with ZooKeeper session.
We only have one ZKRMStateStore but we can have multiple ZK client sessions.
Currently ZKRMStateStore#processWatchEvent doesn't check whether this watcher event is from
current session. So the watcher event from old ZK client session which just is closed will
still be processed.
For example, If a Disconnected event received from old session after new session is connected,
the zkClient will be set to null
{code}
        case Disconnected:
          LOG.info("ZKRMStateStore Session disconnected");
          oldZkClient = zkClient;
          zkClient = null;
          break;
{code}
Then ZKRMStateStore won't receive SyncConnected event from new session because new session
is already in SyncConnected state and it won't send SyncConnected event until it is disconnected
and connected again.
Then we will see all the ZKRMStateStore operations fail with IOException "Wait for ZKClient
creation timed out" until  RM shutdown.

The following code from zookeeper(ClientCnxn#EventThread) show even after receive eventOfDeath,
EventThread will still process all the events until  waitingEvents queue is empty.
{code}
              while (true) {
                 Object event = waitingEvents.take();
                 if (event == eventOfDeath) {
                    wasKilled = true;
                 } else {
                    processEvent(event);
                 }
                 if (wasKilled)
                    synchronized (waitingEvents) {
                       if (waitingEvents.isEmpty()) {
                          isRunning = false;
                          break;
                       }
                    }
              }
{code}


> Old ZK client session watcher event messed up new ZK client session due to ZooKeeper
asynchronously closing client session.
> ---------------------------------------------------------------------------------------------------------------------------
>
>                 Key: YARN-3242
>                 URL: https://issues.apache.org/jira/browse/YARN-3242
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: resourcemanager
>    Affects Versions: 2.6.0
>            Reporter: zhihai xu
>            Assignee: zhihai xu
>            Priority: Critical
>         Attachments: YARN-3242.000.patch, YARN-3242.001.patch
>
>
> Old ZK client session watcher event messed up new ZK client session due to ZooKeeper
asynchronously closing client session.
> The watcher event from old ZK client session can still be sent to ZKRMStateStore after
the old  ZK client session is closed.
> This will cause seriously problem:ZKRMStateStore out of sync with ZooKeeper session.
> We only have one ZKRMStateStore but we can have multiple ZK client sessions.
> Currently ZKRMStateStore#processWatchEvent doesn't check whether this watcher event is
from current session. So the watcher event from old ZK client session which just is closed
will still be processed.
> For example, If a Disconnected event received from old session after new session is connected,
the zkClient will be set to null
> {code}
>         case Disconnected:
>           LOG.info("ZKRMStateStore Session disconnected");
>           oldZkClient = zkClient;
>           zkClient = null;
>           break;
> {code}
> Then ZKRMStateStore won't receive SyncConnected event from new session because new session
is already in SyncConnected state and it won't send SyncConnected event until it is disconnected
and connected again.
> Then we will see all the ZKRMStateStore operations fail with IOException "Wait for ZKClient
creation timed out" until  RM shutdown.
> The following code from zookeeper(ClientCnxn#EventThread) show even after receive eventOfDeath,
EventThread will still process all the events until  waitingEvents queue is empty.
> {code}
>               while (true) {
>                  Object event = waitingEvents.take();
>                  if (event == eventOfDeath) {
>                     wasKilled = true;
>                  } else {
>                     processEvent(event);
>                  }
>                  if (wasKilled)
>                     synchronized (waitingEvents) {
>                        if (waitingEvents.isEmpty()) {
>                           isRunning = false;
>                           break;
>                        }
>                     }
>               }
>       private void processEvent(Object event) {
>           try {
>               if (event instanceof WatcherSetEventPair) {
>                   // each watcher will process the event
>                   WatcherSetEventPair pair = (WatcherSetEventPair) event;
>                   for (Watcher watcher : pair.watchers) {
>                       try {
>                           watcher.process(pair.event);
>                       } catch (Throwable t) {
>                           LOG.error("Error while calling watcher ", t);
>                       }
>                   }
>               } else {
> {code}



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