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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-10255) Standby Dispatcher locks submitted JobGraphs
Date Wed, 12 Sep 2018 15:37:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-10255?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16612347#comment-16612347
] 

ASF GitHub Bot commented on FLINK-10255:
----------------------------------------

GJL commented on a change in pull request #6678: [FLINK-10255] Only react to onAddedJobGraph
signal when being leader
URL: https://github.com/apache/flink/pull/6678#discussion_r217082586
 
 

 ##########
 File path: flink-runtime/src/main/java/org/apache/flink/runtime/dispatcher/Dispatcher.java
 ##########
 @@ -879,24 +917,66 @@ public void handleError(final Exception exception) {
 
 	@Override
 	public void onAddedJobGraph(final JobID jobId) {
-		final CompletableFuture<SubmittedJobGraph> recoveredJob = getRpcService().execute(
-			() -> submittedJobGraphStore.recoverJobGraph(jobId));
-
-		final CompletableFuture<Acknowledge> submissionFuture = recoveredJob.thenComposeAsync(
-			(SubmittedJobGraph submittedJobGraph) -> submitJob(submittedJobGraph.getJobGraph(),
RpcUtils.INF_TIMEOUT),
-			getMainThreadExecutor());
-
-		submissionFuture.whenComplete(
-			(Acknowledge acknowledge, Throwable throwable) -> {
-				if (throwable != null) {
-					onFatalError(
-						new DispatcherException(
-							String.format("Could not start the added job %s", jobId),
-							ExceptionUtils.stripCompletionException(throwable)));
+		runAsync(
+			() -> {
+				if (!jobManagerRunners.containsKey(jobId)) {
+					final CompletableFuture<JobGraph> recoveredJob = recoveryOperation.thenApplyAsync(
+						ignored -> {
+							try {
+								return recoverJob(jobId);
+							} catch (Exception e) {
+								ExceptionUtils.rethrow(e);
+							}
+							return null;
+						},
+						getRpcService().getExecutor());
+
+					final DispatcherId dispatcherId = getFencingToken();
+					final CompletableFuture<Void> submissionFuture = recoveredJob.thenComposeAsync(
+						(FunctionWithThrowable<JobGraph, CompletableFuture<Void>, Exception>) (JobGraph
jobGraph) -> tryRunRecoveredJobGraph(jobGraph, dispatcherId)
+							.thenAcceptAsync(
+								(ConsumerWithException<Boolean, Exception>) (Boolean isRecoveredJobRunning)
-> {
 
 Review comment:
   Imo we are doing this wrong. The API would be much more readible with static factory methods:
   
   ```
   
   /**
    * {@link Consumer} that can throw checked exceptions.
    */
   @FunctionalInterface
   public interface CheckedConsumer<T> {
   
   	void checkedAccept(T t) throws Exception;
   
   	static <T> Consumer<T> unchecked(CheckedConsumer<T> checkedConsumer)
{
   		return (t) -> {
   			try {
   				checkedConsumer.checkedAccept(t);
   			} catch (Exception e) {
   				ExceptionUtils.rethrow(e);
   			}
   		};
   	}
   }
   ```
   This allows for:
   ```
   CheckedConsumer.unchecked(isRecoveredJobRunning -> {
        ...
   });
   ``` 
   No casts are required. Also when interacting with the Java API, it does not matter what
exact type of exception can be thrown – what matters is that the checked exception becomes
a unchecked. We do not need to generify the exception type in `ConsumerWithException`. 

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> Standby Dispatcher locks submitted JobGraphs
> --------------------------------------------
>
>                 Key: FLINK-10255
>                 URL: https://issues.apache.org/jira/browse/FLINK-10255
>             Project: Flink
>          Issue Type: Bug
>          Components: Distributed Coordination
>    Affects Versions: 1.5.3, 1.6.0, 1.7.0
>            Reporter: Till Rohrmann
>            Assignee: Till Rohrmann
>            Priority: Blocker
>              Labels: pull-request-available
>             Fix For: 1.6.1, 1.7.0, 1.5.4
>
>
> Currently, standby {{Dispatchers}} lock submitted {{JobGraphs}} which are added to the
{{SubmittedJobGraphStore}} if HA mode is enabled. Locking the {{JobGraphs}} can prevent their
cleanup leaving the system in an inconsistent state.
> The problem is that we recover in the {{SubmittedJobGraphListener#onAddedJobGraph}} callback
which is also called if don't have the leadership the newly added {{JobGraph}}. Recovering
the {{JobGraph}} currently locks the {{JobGraph}}. In case that the {{Dispatcher}} is not
the leader, then we won't start that job after its recovery. However, we also don't release
the {{JobGraph}} leaving it locked.
> There are two possible solutions to the problem. Either we check whether we are the leader
before recovering jobs or we say that recovering jobs does not lock them. Only if we can submit
the recovered job we lock them. The latter approach has the advantage that it follows a quite
similar code path as an initial job submission. Moreover, jobs are currently also recovered
at other places. In all these places we currently would need to release the {{JobGraphs}}
if we cannot submit the recovered {{JobGraph}} (e.g. {{Dispatcher#grantLeadership}}).
> An extension of the first solution could be to stop the {{SubmittedJobGraphStore}} while
the {{Dispatcher}} is not the leader. Then we would have to make sure that no concurrent callback
from the {{SubmittedJobGraphStore#SubmittedJobGraphListener}} can be executed after revoking
leadership from the {{Dispatcher}}.



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