GJL commented on a change in pull request #8922: [FLINK-12876][runtime] Add an 
adapter of region failover NG for legacy scheduler
URL: https://github.com/apache/flink/pull/8922#discussion_r299867622
 
 

 ##########
 File path: 
flink-runtime/src/main/java/org/apache/flink/runtime/executiongraph/failover/AdaptedRestartPipelinedRegionStrategyNG.java
 ##########
 @@ -0,0 +1,316 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.runtime.executiongraph.failover;
+
+import org.apache.flink.annotation.VisibleForTesting;
+import org.apache.flink.runtime.JobException;
+import org.apache.flink.runtime.checkpoint.CheckpointException;
+import org.apache.flink.runtime.checkpoint.CheckpointFailureReason;
+import org.apache.flink.runtime.concurrent.FutureUtils;
+import org.apache.flink.runtime.executiongraph.Execution;
+import org.apache.flink.runtime.executiongraph.ExecutionGraph;
+import org.apache.flink.runtime.executiongraph.ExecutionJobVertex;
+import org.apache.flink.runtime.executiongraph.ExecutionVertex;
+import org.apache.flink.runtime.executiongraph.GlobalModVersionMismatch;
+import org.apache.flink.runtime.executiongraph.SchedulingUtils;
+import 
org.apache.flink.runtime.executiongraph.failover.adapter.DefaultFailoverTopology;
+import 
org.apache.flink.runtime.executiongraph.failover.flip1.RestartPipelinedRegionStrategy;
+import org.apache.flink.runtime.jobgraph.JobStatus;
+import org.apache.flink.runtime.jobgraph.JobVertexID;
+import org.apache.flink.runtime.jobmanager.scheduler.CoLocationGroup;
+import org.apache.flink.runtime.scheduler.ExecutionVertexVersion;
+import org.apache.flink.runtime.scheduler.ExecutionVertexVersioner;
+import org.apache.flink.runtime.scheduler.strategy.ExecutionVertexID;
+import org.apache.flink.util.ExceptionUtils;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.CancellationException;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
+import java.util.function.BiFunction;
+import java.util.stream.Collectors;
+
+import static org.apache.flink.util.Preconditions.checkNotNull;
+import static org.apache.flink.util.Preconditions.checkState;
+
+/**
+ * This failover strategy uses flip1.RestartPipelinedRegionStrategy to make 
task failover decisions.
+ */
+public class AdaptedRestartPipelinedRegionStrategyNG extends FailoverStrategy {
+
+       private static final Logger LOG = 
LoggerFactory.getLogger(AdaptedRestartPipelinedRegionStrategyNG.class);
+
+       /** The execution graph on which this FailoverStrategy works. */
+       private final ExecutionGraph executionGraph;
+
+       /** The versioner helps to maintain execution vertex versions. */
+       private final ExecutionVertexVersioner executionVertexVersioner;
+
+       /** The underlying new generation region failover strategy. */
+       private RestartPipelinedRegionStrategy restartPipelinedRegionStrategy;
+
+       public AdaptedRestartPipelinedRegionStrategyNG(final ExecutionGraph 
executionGraph) {
+               this.executionGraph = checkNotNull(executionGraph);
+               this.executionVertexVersioner = new ExecutionVertexVersioner();
+       }
+
+       @Override
+       public void onTaskFailure(final Execution taskExecution, final 
Throwable cause) {
+               if (!executionGraph.getRestartStrategy().canRestart()) {
+                       // delegate the failure to a global fail that will 
check the restart strategy and not restart
+                       LOG.info("Fail to pass the restart strategy validation 
in region failover. Fallback to fail global.");
+                       failGlobal(cause);
+                       return;
+               }
+
+               if 
(!isLocalFailoverValid(executionGraph.getGlobalModVersion())) {
+                       LOG.info("Skip current region failover as a global 
failover is ongoing.");
+                       return;
+               }
+
+               final ExecutionVertexID vertexID = 
getExecutionVertexID(taskExecution.getVertex());
+
+               final Set<ExecutionVertexID> tasksToRestart = 
restartPipelinedRegionStrategy.getTasksNeedingRestart(vertexID, cause);
+               restartTasks(tasksToRestart);
+       }
+
+       @VisibleForTesting
+       protected void restartTasks(final Set<ExecutionVertexID> 
verticesToRestart) {
+               final long globalModVersion = 
executionGraph.getGlobalModVersion();
+               final Set<ExecutionVertexVersion> vertexVersions = new 
HashSet<>(
+                       
executionVertexVersioner.recordVertexModifications(verticesToRestart).values());
+
+               FutureUtils.assertNoException(
+                       cancelTasks(verticesToRestart)
+                               
.thenRunAsync(resetAndRescheduleTasks(globalModVersion, vertexVersions), 
executionGraph.getJobMasterMainThreadExecutor())
+                               .handle(failGlobalOnError()));
+       }
+
+       private Runnable resetAndRescheduleTasks(final long globalModVersion, 
final Set<ExecutionVertexVersion> vertexVersions) {
+               return () -> {
+                       if (!isLocalFailoverValid(globalModVersion)) {
+                               LOG.info("Skip current region failover as a 
global failover is ongoing.");
+                               return;
+                       }
+
+                       // found out vertices which are still valid to restart.
+                       // some vertices involved in this failover may be 
modified if another region
+                       // failover happens during the cancellation stage of 
this failover.
+                       // Will ignore the modified vertices as the other 
failover will deal with them.
+                       final Set<ExecutionVertex> unmodifiedVertices = 
executionVertexVersioner
+                               .getUnmodifiedExecutionVertices(vertexVersions)
+                               .stream()
+                               .map(this::getExecutionVertex)
+                               .collect(Collectors.toSet());
+
+                       try {
+                               LOG.info("Finally restart {} tasks to recover 
from task failure.", unmodifiedVertices.size());
+
+                               // reset tasks to CREATED state and reload state
+                               resetTasks(unmodifiedVertices, 
globalModVersion);
+
+                               // re-schedule tasks
+                               rescheduleTasks(unmodifiedVertices, 
globalModVersion);
+                       } catch (GlobalModVersionMismatch e) {
+                               // happens when a global recovery happens 
concurrently to the regional recovery
+                               // just stop this local failover
 
 Review comment:
   Replaced comment with `IllegalStateException`. `GlobalModVersionMismatch` 
should be cleaned up in a separate ticket.

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