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From: uce <git@git.apache.org>
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Subject: [GitHub] flink pull request: [FLINK-2354] Add job graph and
 checkpoint reco...
Content-Type: text/plain
Message-Id: <20151008153244.71118E0BD2@git1-us-west.apache.org>
Date: Thu,  8 Oct 2015 15:32:44 +0000 (UTC)

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

    https://github.com/apache/flink/pull/1153#discussion_r41528652
  
    --- Diff: flink-runtime/src/main/java/org/apache/flink/runtime/checkpoint/ZooKeeperCompletedCheckpointStore.java ---
    @@ -0,0 +1,310 @@
    +/*
    + * 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.checkpoint;
    +
    +import org.apache.curator.framework.CuratorFramework;
    +import org.apache.curator.framework.api.BackgroundCallback;
    +import org.apache.curator.framework.api.CuratorEvent;
    +import org.apache.curator.framework.api.CuratorEventType;
    +import org.apache.curator.utils.ZKPaths;
    +import org.apache.flink.runtime.jobmanager.RecoveryMode;
    +import org.apache.flink.runtime.state.StateHandleProvider;
    +import org.apache.flink.runtime.zookeeper.ZooKeeperStateHandleStore;
    +import org.apache.flink.runtime.zookeeper.ZooKeeperStateHandleStore.ZooKeeperStateHandle;
    +import org.apache.zookeeper.data.Stat;
    +import org.slf4j.Logger;
    +import org.slf4j.LoggerFactory;
    +
    +import java.util.ArrayDeque;
    +import java.util.ArrayList;
    +import java.util.ConcurrentModificationException;
    +import java.util.List;
    +
    +import static com.google.common.base.Preconditions.checkArgument;
    +import static com.google.common.base.Preconditions.checkNotNull;
    +
    +/**
    + * {@link CompletedCheckpointStore} for JobManagers running in {@link RecoveryMode#ZOOKEEPER}.
    + *
    + * <p>Checkpoints are added under a ZNode per job:
    + * <pre>
    + * +----O /flink/checkpoints/&lt;job-id&gt;  [persistent]
    + * .    |
    + * .    +----O /flink/checkpoints/&lt;job-id&gt;/1 [persistent_sequential]
    + * .    .                                  .
    + * .    .                                  .
    + * .    .                                  .
    + * .    +----O /flink/checkpoints/&lt;job-id&gt;/N [persistent_sequential]
    + * </pre>
    + *
    + * <p>During recovery, the latest checkpoint is read from ZooKeeper. If there is more than one,
    + * only the latest one is used and older ones are discarded (even if the maximum number
    + * of retained checkpoints is greater than one). The sequential; cversion determines, which
    + * checkpoint is the latest one.
    + *
    + * <p>If there is a network partition and multiple JobManagers run concurrent checkpoints for the
    + * same program, it is OK to take any valid successful checkpoint as long as the "history" of
    + * checkpoints is consistent. Currently, after recovery we start out with only a single
    + * checkpoint in oder to guarantee this.
    + */
    +public class ZooKeeperCompletedCheckpointStore implements CompletedCheckpointStore {
    +
    +	private static final Logger LOG = LoggerFactory.getLogger(ZooKeeperCompletedCheckpointStore.class);
    +
    +	/** Curator ZooKeeper client */
    +	private final CuratorFramework client;
    +
    +	/** Completed checkpoints in ZooKeeper */
    +	private final ZooKeeperStateHandleStore<CompletedCheckpoint> checkpointsInZooKeeper;
    +
    +	/** The maximum number of checkpoints to retain (at least 1). */
    +	private final int maxNumberOfCheckpointsToRetain;
    +
    +	/** User class loader for discarding {@link CompletedCheckpoint} instances. */
    +	private final ClassLoader userClassLoader;
    +
    +	/** Local completed checkpoints. */
    +	private final ArrayDeque<ZooKeeperStateHandle<CompletedCheckpoint>> checkpointStateHandles;
    +
    +	/**
    +	 * Creates a {@link ZooKeeperCompletedCheckpointStore} instance.
    +	 *
    +	 * @param maxNumberOfCheckpointsToRetain The maximum number of checkpoints to retain (at
    +	 *                                       least 1). Adding more checkpoints than this results
    +	 *                                       in older checkpoints being discarded. On recovery,
    +	 *                                       we will only start with a single checkpoint.
    +	 * @param userClassLoader                The user class loader used to discard checkpoints
    +	 * @param client                         The Curator ZooKeeper client
    +	 * @param checkpointsPath                The ZooKeeper path for the checkpoints (needs to
    +	 *                                       start with a '/')
    +	 * @param stateHandleProvider            The state handle provider for checkpoints
    +	 * @throws Exception
    +	 */
    +	public ZooKeeperCompletedCheckpointStore(
    +			int maxNumberOfCheckpointsToRetain,
    +			ClassLoader userClassLoader,
    +			CuratorFramework client,
    +			String checkpointsPath,
    +			StateHandleProvider<CompletedCheckpoint> stateHandleProvider) throws Exception {
    +
    +		checkArgument(maxNumberOfCheckpointsToRetain >= 1, "Must retain at least one checkpoint.");
    +
    +		this.maxNumberOfCheckpointsToRetain = maxNumberOfCheckpointsToRetain;
    +		this.userClassLoader = checkNotNull(userClassLoader, "User class loader");
    +
    +		checkNotNull(client, "Curator client");
    +		checkNotNull(checkpointsPath, "Checkpoints path");
    +		checkNotNull(stateHandleProvider, "State handle provider");
    +
    +		// Ensure that the checkpoints path exists
    +		client.newNamespaceAwareEnsurePath(checkpointsPath)
    +				.ensure(client.getZookeeperClient());
    +
    +		// All operations will have the path as root
    +		this.client = client.usingNamespace(client.getNamespace() + checkpointsPath);
    +
    +		this.checkpointsInZooKeeper = new ZooKeeperStateHandleStore<>(
    +				this.client, stateHandleProvider);
    +
    +		this.checkpointStateHandles = new ArrayDeque<>(maxNumberOfCheckpointsToRetain + 1);
    +
    +		LOG.info("Initialized in '{}'.", checkpointsPath);
    +	}
    +
    +	/**
    +	 * Gets the latest checkpoint from ZooKeeper and removes all others.
    +	 *
    +	 * <p><strong>Important</strong>: Even if there are more than one checkpoint in ZooKeeper,
    +	 * this will only recover the latest and discard the others. Otherwise, there is no guarantee
    +	 * that the history of checkpoints is consistent.
    +	 */
    +	@Override
    +	public void recover() throws Exception {
    +		LOG.info("Recovering checkpoints from ZooKeeper.");
    +
    +		// Get all there is first
    +		List<ZooKeeperStateHandle<CompletedCheckpoint>> initialCheckpoints;
    +		while (true) {
    +			try {
    +				initialCheckpoints = checkpointsInZooKeeper.getAllSortedByName();
    +				break;
    +			}
    +			catch (ConcurrentModificationException e) {
    +				LOG.warn("Concurrent modification while reading from ZooKeeper. Retrying.");
    +			}
    +		}
    +
    +		int numberOfInitialCheckpoints = initialCheckpoints.size();
    +
    +		LOG.info("Found {} checkpoints in ZooKeeper.", numberOfInitialCheckpoints);
    +
    +		if (numberOfInitialCheckpoints > 0) {
    +			// Take the last one. This is the latest checkpoints, because path names are strictly
    +			// increasing (checkpoint ID).
    +			ZooKeeperStateHandle<CompletedCheckpoint> latest = initialCheckpoints
    +					.get(numberOfInitialCheckpoints - 1);
    +
    +			CompletedCheckpoint latestCheckpoint = latest.getState(userClassLoader);
    +
    +			checkpointStateHandles.add(latest);
    +
    +			LOG.info("Initialized with {}. Removing all older checkpoints.", latestCheckpoint);
    +
    +			for (int i = 0; i < numberOfInitialCheckpoints - 1; i++) {
    +				try {
    +					removeFromZooKeeperAndDiscardCheckpoint(initialCheckpoints.get(i));
    +				}
    +				catch (Exception e) {
    +					LOG.error("Failed to discard checkpoint", e);
    +				}
    +			}
    +		}
    +	}
    +
    +	@Override
    +	public int getNextCheckpointID() throws Exception {
    --- End diff --
    
    It is! What can we do about it if we don't count in ZooKeeper as before?


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