Github user tillrohrmann commented on a diff in the pull request:

    https://github.com/apache/flink/pull/4916#discussion_r148216607
  
    --- Diff: 
flink-runtime/src/main/java/org/apache/flink/runtime/executiongraph/ExecutionGraph.java
 ---
    @@ -878,113 +880,70 @@ private void scheduleEager(SlotProvider 
slotProvider, final Time timeout) {
                // that way we do not have any operation that can fail between 
allocating the slots
                // and adding them to the list. If we had a failure in between 
there, that would
                // cause the slots to get lost
    -           final ArrayList<ExecutionAndSlot[]> resources = new 
ArrayList<>(getNumberOfExecutionJobVertices());
                final boolean queued = allowQueuedScheduling;
     
    -           // we use this flag to handle failures in a 'finally' clause
    -           // that allows us to not go through clumsy cast-and-rethrow 
logic
    -           boolean successful = false;
    +           // collecting all the slots may resize and fail in that 
operation without slots getting lost
    +           final ArrayList<CompletableFuture<Execution>> 
allAllocationFutures = new ArrayList<>(getNumberOfExecutionJobVertices());
     
    -           try {
    -                   // collecting all the slots may resize and fail in that 
operation without slots getting lost
    -                   final ArrayList<CompletableFuture<SimpleSlot>> 
slotFutures = new ArrayList<>(getNumberOfExecutionJobVertices());
    +           // allocate the slots (obtain all their futures
    +           for (ExecutionJobVertex ejv : getVerticesTopologically()) {
    +                   // these calls are not blocking, they only return 
futures
    --- End diff --
    
    In that case, it depends a bit on how the scheduler values the state 
location preference. If it is implemented that it strictly schedules tasks to 
its previous state location, then it could happen that these tasks don't end up 
in the same slot as other tasks with which they shared a slot before.


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