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From "MaoYuan Xian (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HAMA-780) New launched child processes by fault tolerance may not be able to contact each other
Date Mon, 22 Jul 2013 03:40:48 GMT

     [ https://issues.apache.org/jira/browse/HAMA-780?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

MaoYuan Xian updated HAMA-780:
------------------------------

    Resolution: Fixed
        Status: Resolved  (was: Patch Available)
    
> New launched child processes by fault tolerance may not be able to contact each other
> -------------------------------------------------------------------------------------
>
>                 Key: HAMA-780
>                 URL: https://issues.apache.org/jira/browse/HAMA-780
>             Project: Hama
>          Issue Type: Bug
>          Components: bsp core
>    Affects Versions: 0.6.2
>            Reporter: MaoYuan Xian
>            Assignee: MaoYuan Xian
>         Attachments: HAMA-780.patch
>
>
> When fault tolerance enabled, sometimes recovery process fail because of new launched
child process can not send message to each other.
> I can finally find the cause:
> On one hand, when a new child process is launched for recovery, its port is set via following
logic:
> {code}
>       final BSPTask task = (BSPTask) umbilical.getTask(taskid);
>       int peerPort = umbilical.getAssignedPortNum(taskid);
>       ...
>       defaultConf.setInt(Constants.PEER_PORT, peerPort);
> {code}
> These logic will find the lowest available port for new comming process:
> {code}
>   public static int getNextAvailable(int fromPort) {
>     ...
>     for (int i = fromPort + 1; i <= MAX_PORT_NUMBER; i++) {
>       if (available(i)) {
>         return i;
>       }
>     }
>     ...
>   }
> {code}
> List a use case here:
> Run one job with 3 child tasks, they are listening to hostname:61001, hostname:61002,
hostname:61003
> In case the task listens to hostname:61002 failed (because of disk problem or kill by
system's memory protection program), the 61002 port is release now.
> Recovery process start, trigger three new processes, assign to the addresses hostname:61002,
hostname:61004, hostname:61005. (61001, 61003 is still be held by old child task before they
quit).
> During this recovery phase, we can find the /bsp/job_id/peers directory in zookeeper
is something like
> {quote}
> hostname:61001, hostname:61002, hostname:61005, hostname:61003, hostname:61004
> {quote}
> One the other hand, new launched child processes try to find each other from zookeeper
when they are launch (in BSPPeerImpl.java):
> {code}
>   private final void initPeerNames() {
>     if (allPeers == null) {
>       allPeers = syncClient.getAllPeerNames(taskId);
>     }
>   }
> {code}
> {code}
>   public String[] getAllPeerNames(TaskAttemptID taskId) {
>     if (allPeers == null) {
>       TreeMap<Integer, String> sortedMap = new TreeMap<Integer, String>();
>       try {
>         List<String> var = zk.getChildren(
>             constructKey(taskId.getJobID(), "peers"), this);
>         allPeers = var.toArray(new String[var.size()]);
>         for (String s : allPeers) {
>           ...
>           boolean result = getValueFromBytes(data, thatTask);
>           if (result) {
>             LOG.debug("TASK mapping from zookeeper: " + thatTask + " ID:"
>                 + thatTask.getTaskID().getId() + " : " + s);
>             sortedMap.put(thatTask.getTaskID().getId(), s);
>           }
>         }
>       } catch (Exception e) {
>         LOG.error(e);
>         throw new RuntimeException("All peer names could not be retrieved!");
>       }
>     ...
>   }
> {code}
> Open the log, we can find the following:
> {quote}
> 13/07/13 00:03:39 DEBUG sync.ZooKeeperSyncClientImpl: TASK mapping from zookeeper: attempt_201307122024_0005_000001_0
ID:1 : hostname:61001
> 13/07/13 00:03:39 DEBUG sync.ZooKeeperSyncClientImpl: TASK mapping from zookeeper: attempt_201307122024_0005_000000_1
ID:0 : hostname:61002
> 13/07/13 00:03:39 DEBUG sync.ZooKeeperSyncClientImpl: TASK mapping from zookeeper: attempt_201307122024_0005_000002_1
ID:2 : hostname:61005
> 13/07/13 00:03:39 DEBUG sync.ZooKeeperSyncClientImpl: TASK mapping from zookeeper: attempt_201307122024_0005_000002_0
ID:2 : hostname:61003
> 13/07/13 00:03:39 DEBUG sync.ZooKeeperSyncClientImpl: TASK mapping from zookeeper: attempt_201307122024_0005_000001_1
ID:1 : hostname:61004
> {quote}
> New adding peer hostname:61005 is put before the hostname:61003, which make the sortedMap
in ZooKeeperSyncClientImpl has the map <2, hostname:61003> (the above code sortedMap.put(thatTask.getTaskID().getId(),
s) makes this happen). The new round of processes communication will run into mal-function
because the message should be sent to "hostname:61005" will be sent to "hostname:61003"

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