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From uce <...@git.apache.org>
Subject [GitHub] flink pull request: [FLINK-2354] Add job graph and checkpoint reco...
Date Wed, 07 Oct 2015 14:35:35 GMT
Github user uce commented on a diff in the pull request:

    https://github.com/apache/flink/pull/1153#discussion_r41397436
  
    --- Diff: flink-runtime/src/main/java/org/apache/flink/runtime/checkpoint/ZooKeeperCheckpointIDCounter.java
---
    @@ -0,0 +1,130 @@
    +/*
    + * 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.recipes.shared.SharedCount;
    +import org.apache.curator.framework.recipes.shared.VersionedValue;
    +import org.apache.curator.framework.state.ConnectionState;
    +import org.apache.curator.framework.state.ConnectionStateListener;
    +import org.apache.flink.runtime.jobmanager.RecoveryMode;
    +import org.slf4j.Logger;
    +import org.slf4j.LoggerFactory;
    +
    +import static com.google.common.base.Preconditions.checkNotNull;
    +
    +/**
    + * {@link CheckpointIDCounter} instances for JobManagers running in {@link RecoveryMode#ZOOKEEPER}.
    + *
    + * <p>Each counter creates a ZNode:
    + * <pre>
    + * +----O /flink/checkpoint-counter/&lt;job-id&gt; 1 [persistent]
    + * .
    + * .
    + * .
    + * +----O /flink/checkpoint-counter/&lt;job-id&gt; N [persistent]
    + * </pre>
    + *
    + * <p>The checkpoints IDs are required to be ascending (per job). In order to guarantee
this in case
    + * of job manager failures we use ZooKeeper to have a shared counter across job manager
instances.
    + */
    +public class ZooKeeperCheckpointIDCounter implements CheckpointIDCounter {
    +
    +	private static final Logger LOG = LoggerFactory.getLogger(ZooKeeperCheckpointIDCounter.class);
    +
    +	/** Curator ZooKeeper client */
    +	private final CuratorFramework client;
    +
    +	/** Path of the shared count */
    +	private final String counterPath;
    +
    +	/** Curator recipe for shared counts */
    +	private final SharedCount sharedCount;
    +
    +	/** Connection state listener to monitor the client connection */
    +	private final SharedCountConnectionStateListener connStateListener =
    +			new SharedCountConnectionStateListener();
    +
    +	/**
    +	 * Creates a {@link ZooKeeperCheckpointIDCounter} instance.
    +	 *
    +	 * @param client      Curator ZooKeeper client
    +	 * @param counterPath ZooKeeper path for the counter. It's sufficient to have a path
per-job.
    +	 * @throws Exception
    +	 */
    +	public ZooKeeperCheckpointIDCounter(CuratorFramework client, String counterPath) throws
Exception {
    +		this.client = checkNotNull(client, "Curator client");
    +		this.counterPath = checkNotNull(counterPath, "Counter path");
    +		this.sharedCount = new SharedCount(client, counterPath, 1);
    +	}
    +
    +	@Override
    +	public void start() throws Exception {
    +		sharedCount.start();
    +		client.getConnectionStateListenable().addListener(connStateListener);
    +	}
    +
    +	@Override
    +	public void stop() throws Exception {
    +		sharedCount.close();
    +		client.getConnectionStateListenable().removeListener(connStateListener);
    +
    +		LOG.info("Removing {} from ZooKeeper", counterPath);
    +		client.delete().deletingChildrenIfNeeded().inBackground().forPath(counterPath);
    +	}
    +
    +	@Override
    +	public long getAndIncrement() throws Exception {
    +		while (true) {
    +			ConnectionState connState = connStateListener.getLastState();
    +
    +			if (connState != null) {
    +				throw new IllegalStateException("Connection state: " + connState);
    +			}
    +
    +			VersionedValue<Integer> current = sharedCount.getVersionedValue();
    +
    +			Integer newCount = current.getValue() + 1;
    +
    +			if (sharedCount.trySetCount(current, newCount)) {
    +				return current.getValue();
    +			}
    +		}
    +	}
    +
    +	/**
    +	 * Connection state listener. In case of {@link ConnectionState#SUSPENDED} or {@link
    +	 * ConnectionState#LOST} we are not guaranteed to read a current count from ZooKeeper.
    +	 */
    +	private class SharedCountConnectionStateListener implements ConnectionStateListener
{
    +
    +		private volatile ConnectionState lastState;
    +
    +		@Override
    +		public void stateChanged(CuratorFramework client, ConnectionState newState) {
    +			if (newState == ConnectionState.SUSPENDED || newState == ConnectionState.LOST) {
    --- End diff --
    
    The checkpoint ID counter will be removed (see conversation).


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