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Date: Thu, 8 Oct 2015 16:32:26 +0000 (UTC)
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 <JIRA.12844948.1436880638417@arcas>
Subject: [jira] [Commented] (FLINK-2354) Recover running jobs on JobManager
 failure
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    [ https://issues.apache.org/jira/browse/FLINK-2354?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14948952#comment-14948952 ] 

ASF GitHub Bot commented on FLINK-2354:
---------------------------------------

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

    https://github.com/apache/flink/pull/1153#discussion_r41536137
  
    --- Diff: flink-runtime/src/main/java/org/apache/flink/runtime/jobmanager/ZooKeeperSubmittedJobGraphStore.java ---
    @@ -0,0 +1,380 @@
    +/*
    + * 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.jobmanager;
    +
    +import org.apache.curator.framework.CuratorFramework;
    +import org.apache.curator.framework.recipes.cache.PathChildrenCache;
    +import org.apache.curator.framework.recipes.cache.PathChildrenCacheEvent;
    +import org.apache.curator.framework.recipes.cache.PathChildrenCacheListener;
    +import org.apache.curator.utils.ZKPaths;
    +import org.apache.flink.api.common.JobID;
    +import org.apache.flink.runtime.state.StateHandle;
    +import org.apache.flink.runtime.state.StateHandleProvider;
    +import org.apache.flink.runtime.zookeeper.ZooKeeperStateHandleStore;
    +import org.apache.zookeeper.KeeperException;
    +import org.slf4j.Logger;
    +import org.slf4j.LoggerFactory;
    +import scala.Option;
    +
    +import java.util.ArrayList;
    +import java.util.Collections;
    +import java.util.ConcurrentModificationException;
    +import java.util.HashSet;
    +import java.util.List;
    +import java.util.Set;
    +
    +import static com.google.common.base.Preconditions.checkNotNull;
    +import static com.google.common.base.Preconditions.checkState;
    +
    +/**
    + * {@link SubmittedJobGraph} instances for JobManagers running in {@link RecoveryMode#ZOOKEEPER}.
    + *
    + * <p>Each job graph creates ZNode:
    + * <pre>
    + * +----O /flink/jobgraphs/&lt;job-id&gt; 1 [persistent]
    + * .
    + * .
    + * .
    + * +----O /flink/jobgraphs/&lt;job-id&gt; N [persistent]
    + * </pre>
    + *
    + * <p>The root path is watched to detect concurrent modifications in corner situations where
    + * multiple instances operate concurrently. The job manager acts as a {@link SubmittedJobGraphListener}
    + * to react to such situations.
    + */
    +public class ZooKeeperSubmittedJobGraphStore implements SubmittedJobGraphStore {
    +
    +	private static final Logger LOG = LoggerFactory.getLogger(ZooKeeperSubmittedJobGraphStore.class);
    +
    +	/** Lock to synchronize with the {@link SubmittedJobGraphListener}. */
    +	private final Object cacheLock = new Object();
    +
    +	/** Client (not a namespace facade) */
    +	private final CuratorFramework client;
    +
    +	/** The set of IDs of all added job graphs. */
    +	private final Set<JobID> addedJobGraphs = new HashSet<>();
    +
    +	/** Completed checkpoints in ZooKeeper */
    +	private final ZooKeeperStateHandleStore<SubmittedJobGraph> jobGraphsInZooKeeper;
    +
    +	/**
    +	 * Cache to monitor all children. This is used to detect races with other instances working
    +	 * on the same state.
    +	 */
    +	private final PathChildrenCache pathCache;
    +
    +	/** The external listener to be notified on races. */
    +	private SubmittedJobGraphListener jobGraphListener;
    +
    +	/** Flag indicating whether this instance is running. */
    +	private boolean isRunning;
    +
    +	public ZooKeeperSubmittedJobGraphStore(
    +			CuratorFramework client,
    +			String currentJobsPath,
    +			StateHandleProvider<SubmittedJobGraph> stateHandleProvider) throws Exception {
    +
    +		checkNotNull(currentJobsPath, "Current jobs path");
    +		checkNotNull(stateHandleProvider, "State handle provider");
    +
    +		// Keep a reference to the original client and not the namespace facade. The namespace
    +		// facade cannot be closed.
    +		this.client = checkNotNull(client, "Curator client");
    +
    +		// Ensure that the job graphs path exists
    +		client.newNamespaceAwareEnsurePath(currentJobsPath)
    +				.ensure(client.getZookeeperClient());
    +
    +		// All operations will have the path as root
    +		client = client.usingNamespace(client.getNamespace() + currentJobsPath);
    +
    +		this.jobGraphsInZooKeeper = new ZooKeeperStateHandleStore<>(client, stateHandleProvider);
    +
    +		this.pathCache = new PathChildrenCache(client, "/", false);
    +		pathCache.getListenable().addListener(new SubmittedJobGraphsPathCacheListener());
    +	}
    +
    +	@Override
    +	public void start(SubmittedJobGraphListener jobGraphListener) throws Exception {
    +		synchronized (cacheLock) {
    +			if (!isRunning) {
    +				this.jobGraphListener = jobGraphListener;
    +
    +				pathCache.start();
    +
    +				isRunning = true;
    +			}
    +		}
    +	}
    +
    +	@Override
    +	public void stop() throws Exception {
    +		synchronized (cacheLock) {
    +			if (isRunning) {
    +				jobGraphListener = null;
    +
    +				pathCache.close();
    +
    +				client.close();
    +
    +				isRunning = false;
    +			}
    +		}
    +	}
    +
    +	@Override
    +	public List<SubmittedJobGraph> recoverJobGraphs() throws Exception {
    +		synchronized (cacheLock) {
    +			verifyIsRunning();
    +
    +			List<ZooKeeperStateHandleStore.ZooKeeperStateHandle<SubmittedJobGraph>> submitted;
    +
    +			while (true) {
    +				try {
    +					submitted = jobGraphsInZooKeeper.getAll();
    +					break;
    +				}
    +				catch (ConcurrentModificationException e) {
    +					LOG.warn("Concurrent modification while reading from ZooKeeper. Retrying.");
    +				}
    +			}
    +
    +			if (submitted.size() != 0) {
    +				List<SubmittedJobGraph> jobGraphs = new ArrayList<>(submitted.size());
    +
    +				for (ZooKeeperStateHandleStore.ZooKeeperStateHandle<SubmittedJobGraph> jobStateHandle : submitted) {
    +					SubmittedJobGraph jobGraph = jobStateHandle
    +							.getState(ClassLoader.getSystemClassLoader());
    +
    +					addedJobGraphs.add(jobGraph.getJobId());
    +
    +					jobGraphs.add(jobGraph);
    +				}
    +
    +				LOG.info("Recovered {} job graphs: {}.", jobGraphs.size(), jobGraphs);
    +				return jobGraphs;
    +			}
    +			else {
    +				LOG.info("No job graph to recover.");
    +				return Collections.emptyList();
    +			}
    +		}
    +	}
    +
    +	@Override
    +	public Option<SubmittedJobGraph> recoverJobGraph(JobID jobId) throws Exception {
    +		checkNotNull(jobId, "Job ID");
    +		String path = getPathForJob(jobId);
    +
    +		synchronized (cacheLock) {
    +			verifyIsRunning();
    +
    +			try {
    +				StateHandle<SubmittedJobGraph> jobStateHandle = jobGraphsInZooKeeper.get(path);
    +
    +				SubmittedJobGraph jobGraph = jobStateHandle
    +						.getState(ClassLoader.getSystemClassLoader());
    +
    +				addedJobGraphs.add(jobGraph.getJobId());
    +
    +				LOG.info("Recovered {}.", jobGraph);
    +
    +				return Option.apply(jobGraph);
    +			}
    +			catch (KeeperException.NoNodeException ignored) {
    +			}
    +
    +			return Option.empty();
    --- End diff --
    
    Resolved


> Recover running jobs on JobManager failure
> ------------------------------------------
>
>                 Key: FLINK-2354
>                 URL: https://issues.apache.org/jira/browse/FLINK-2354
>             Project: Flink
>          Issue Type: Sub-task
>          Components: JobManager
>    Affects Versions: 0.10
>            Reporter: Ufuk Celebi
>            Assignee: Ufuk Celebi
>             Fix For: 0.10
>
>
> tl;dr Persist JobGraphs in state backend and coordinate reference to state handle via ZooKeeper.
> Problem: When running multiple JobManagers in high availability mode, the leading job manager looses all running jobs when it fails. After a new leading job manager is elected, it is not possible to recover any previously running jobs.
> Solution: The leading job manager, which receives the job graph writes 1) the job graph to a state backend, and 2) a reference to the respective state handle to ZooKeeper. In general, job graphs can become large (multiple MBs, because they include closures etc.). ZooKeeper is not designed for data of this size. The level of indirection via the reference to the state backend keeps the data in ZooKeeper small.
> Proposed ZooKeeper layout:
> /flink (default)
>   +- currentJobs
>        +- job id i
>             +- state handle reference of job graph i
> The 'currentJobs' node needs to be persistent to allow recovery of jobs between job managers. The currentJobs node needs to satisfy the following invariant: There is a reference to a job graph with id i IFF the respective job graph needs to be recovered by a newly elected job manager leader.
> With this in place, jobs will be recovered from their initial state (as if resubmitted). The next step is to backup the runtime state handles of checkpoints in a similar manner.
> ---
> This work will be based on [~trohrmann@apache.org]'s implementation of FLINK-2291. The leader election service notifies the job manager about granted/revoked leadership. This notification happens via Akka and thus serially *per* job manager, but results in eventually consistent state between job managers. For some snapshots of time it is possible to have a new leader granted leadership, before the old one has been revoked its leadership.
> [~trohrmann@apache.org], can you confirm that leadership does not guarantee mutually exclusive access to the shared 'currentJobs' state?
> For example, the following can happen:
> - JM 1 is leader, JM 2 is standby
> - JOB i is running (and hence /flink/currentJobs/i exists)
> - ZK notifies leader election service (LES) of JM 1 and JM 2
> - LES 2 immediately notifies JM 2 about granted leadership, but LES 1 notification revoking leadership takes longer
> - JOB i finishes (TMs don't notice leadership change yet) and JM 1 receives final JobStatusChange
> - JM 2 resubmits the job /flink/currentJobs/i
> - JM 1 removes /flink/currentJobs/i, because it is now finished
> => inconsistent state (wrt the specified invariant above)
> If it is indeed a problem, we can circumvent this with a Curator recipe for [shared locks|http://curator.apache.org/curator-recipes/shared-lock.html] to coordinate the access to currentJobs. The lock needs to be acquired on leadership.
> ---
> Minimum required tests:
> - Unit tests for job graph serialization and writing to state backend and ZooKeeper with expected nodes
> - Unit tests for job submission to job manager in leader/non-leader state
> - Unit tests for leadership granting/revoking and job submission/restarting interleavings
> - Process failure integration tests with single and multiple running jobs


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