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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 16:03:26 GMT
Github user uce commented on a diff in the pull request:

    https://github.com/apache/flink/pull/1153#discussion_r41409302
  
    --- Diff: flink-runtime/src/main/java/org/apache/flink/runtime/zookeeper/ZooKeeperStateHandleStore.java
---
    @@ -0,0 +1,422 @@
    +/*
    + * 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.zookeeper;
    +
    +import org.apache.curator.framework.CuratorFramework;
    +import org.apache.curator.framework.api.BackgroundCallback;
    +import org.apache.curator.utils.ZKPaths;
    +import org.apache.flink.runtime.state.StateHandle;
    +import org.apache.flink.runtime.state.StateHandleProvider;
    +import org.apache.flink.util.InstantiationUtil;
    +import org.apache.zookeeper.CreateMode;
    +import org.apache.zookeeper.KeeperException;
    +import org.apache.zookeeper.data.Stat;
    +
    +import java.io.Serializable;
    +import java.util.ArrayList;
    +import java.util.ConcurrentModificationException;
    +import java.util.List;
    +
    +import static com.google.common.base.Preconditions.checkNotNull;
    +
    +/**
    + * State handles backed by ZooKeeper.
    + *
    + * <p>Added state is persisted via {@link StateHandle}s, which in turn are written
to
    + * ZooKeeper. This level of indirection is necessary to keep the amount of data in ZooKeeper
    + * small. ZooKeeper is build for data in the KB range whereas state can grow to multiple
MBs.
    + *
    + * <p>State modifications require some care, because it is possible that certain
failures bring
    + * the state handle backend and ZooKeeper out of sync.
    + *
    + * <p>ZooKeeper holds the ground truth about state handles, i.e. the following
holds:
    + *
    + * <pre>
    + * State handle in ZooKeeper => State handle exists
    + * </pre>
    + *
    + * But not:
    + *
    + * <pre>
    + * State handle exists => State handle in ZooKeeper
    + * </pre>
    + *
    + * There can be lingering state handles when failures happen during operation. They
    + * need to be cleaned up manually (see <a href="https://issues.apache.org/jira/browse/FLINK-2513">
    + * FLINK-2513</a> about a possible way to overcome this).
    + *
    + * @param <T> Type of state
    + */
    +public class ZooKeeperStateHandleStore<T extends Serializable> {
    +
    +	/** Curator ZooKeeper client */
    +	private final CuratorFramework client;
    +
    +	/** State handle provider */
    +	private final StateHandleProvider<T> stateHandleProvider;
    +
    +	/**
    +	 * Creates a {@link ZooKeeperStateHandleStore}.
    +	 *
    +	 * @param client              The Curator ZooKeeper client. <strong>Important:</strong>
It is
    +	 *                            expected that the client's namespace ensures that the
root
    +	 *                            path is exclusive for all state handles managed by this
    +	 *                            instance, e.g. <code>client.usingNamespace("/stateHandles")</code>
    +	 * @param stateHandleProvider The state handle provider for the state
    +	 */
    +	public ZooKeeperStateHandleStore(
    +			CuratorFramework client,
    +			StateHandleProvider<T> stateHandleProvider) {
    +
    +		this.client = checkNotNull(client, "Curator client");
    +		this.stateHandleProvider = checkNotNull(stateHandleProvider, "State handle provider");
    +	}
    +
    +	/**
    +	 * Creates a state handle and stores it in ZooKeeper with create mode {@link
    +	 * CreateMode#PERSISTENT}.
    +	 *
    +	 * @see #add(String, Serializable, CreateMode)
    +	 */
    +	public ZooKeeperStateHandle<T> add(String pathInZooKeeper, T state) throws Exception
{
    +		return add(pathInZooKeeper, state, CreateMode.PERSISTENT);
    +	}
    +
    +	/**
    +	 * Creates a state handle and stores it in ZooKeeper.
    +	 *
    +	 * <p><strong>Important</strong>: This will <em>not</em>
store the actual state in
    +	 * ZooKeeper, but create a state handle and store it in ZooKeeper. This level of indirection
    +	 * makes sure that data in ZooKeeper is small.
    +	 *
    +	 * @param pathInZooKeeper Destination path in ZooKeeper (expected to *not* exist yet
and
    +	 *                        start with a '/')
    +	 * @param state           State to be added
    +	 * @param createMode      The create mode for the new path in ZooKeeper
    +	 * @return Created {@link ZooKeeperStateHandle}
    +	 * @throws Exception
    +	 */
    +	public ZooKeeperStateHandle<T> add(String pathInZooKeeper, T state, CreateMode
createMode) throws Exception {
    +		checkNotNull(pathInZooKeeper, "Path in ZooKeeper");
    +		checkNotNull(state, "State");
    +
    +		// Create the state handle. Nothing persisted yet.
    +		StateHandle<T> stateHandle = stateHandleProvider.createStateHandle(state);
    +
    +		boolean success = false;
    +
    +		try {
    +			// Serialize the state handle. This writes the state to the backend.
    +			byte[] serializedStateHandle = InstantiationUtil.serializeObject(stateHandle);
    +
    +			// Write state handle (not the actual state) to ZooKeeper. This is expected to be
    +			// smaller than the state itself. This level of indirection makes sure that data in
    +			// ZooKeeper is small, because ZooKeeper is designed for data in the KB range, but
    +			// the state can be larger.
    +			client
    +					.create()
    +					.withMode(createMode)
    +					.forPath(pathInZooKeeper, serializedStateHandle);
    +
    +			success = true;
    +
    +			return new ZooKeeperStateHandle<>(stateHandle, pathInZooKeeper);
    +		}
    +		finally {
    +			if (!success) {
    +				// Cleanup the state handle if it was not written to ZooKeeper.
    +				if (stateHandle != null) {
    +					stateHandle.discardState();
    +				}
    +			}
    +		}
    +	}
    +
    +	/**
    +	 * Replaces a state handle in ZooKeeper and discards the old state handle.
    +	 *
    +	 * <p><strong>Important</strong>: This method will only discard the
state handle and not the
    +	 * state itself. Don't forget to run custom cleanup code of the state, if necessary.
    +	 *
    +	 * <pre>
    +	 * T state = get(path).getState();
    +	 * state.discard(); // Custom clean up
    +	 * replace(path, version, newState)
    +	 * </pre>
    +	 *
    +	 * @param pathInZooKeeper Destination path in ZooKeeper (expected to exist and start
with a '/')
    +	 * @param expectedVersion Expected version of the node to replace
    +	 * @param state           The new state to replace the old one
    +	 */
    +	public void replace(String pathInZooKeeper, int expectedVersion, T state) throws Exception
{
    +		checkNotNull(pathInZooKeeper, "Path in ZooKeeper");
    +		checkNotNull(state, "State");
    +
    +		StateHandle<T> oldStateHandle = get(pathInZooKeeper);
    +
    +		StateHandle<T> stateHandle = stateHandleProvider.createStateHandle(state);
    +
    +		boolean success = false;
    +
    +		try {
    +			// Serialize the new state handle. This writes the state to the backend.
    +			byte[] serializedStateHandle = InstantiationUtil.serializeObject(stateHandle);
    +
    +			// Replace state handle in ZooKeeper.
    +			client.setData()
    +					.withVersion(expectedVersion)
    +					.forPath(pathInZooKeeper, serializedStateHandle);
    +
    +			success = true;
    +		}
    +		finally {
    +			if (success) {
    +				oldStateHandle.discardState();
    +			}
    +			else {
    +				stateHandle.discardState();
    +			}
    +		}
    +	}
    +
    +	/**
    +	 * Returns the version of the node if it exists or <code>-1</code> if it
doesn't.
    +	 *
    +	 * @param pathInZooKeeper Path in ZooKeeper to check
    +	 * @return Version of the ZNode if the path exists, <code>-1</code> otherwise.
    +	 * @throws Exception
    +	 */
    +	public int exists(String pathInZooKeeper) throws Exception {
    +		checkNotNull(pathInZooKeeper, "Path in ZooKeeper");
    +
    +		Stat stat = client.checkExists().forPath(pathInZooKeeper);
    +
    +		if (stat != null) {
    +			return stat.getVersion();
    +		}
    +
    +		return -1;
    +	}
    +
    +	/**
    +	 * Gets a state handle from ZooKeeper.
    +	 *
    +	 * @param pathInZooKeeper Path in ZooKeeper to get the state handle from (expected to
    +	 *                        exist and start with a '/').
    +	 * @return The state handle
    +	 * @throws Exception
    +	 */
    +	@SuppressWarnings("unchecked")
    +	public StateHandle<T> get(String pathInZooKeeper) throws Exception {
    +		checkNotNull(pathInZooKeeper, "Path in ZooKeeper");
    +
    +		byte[] data = client.getData().forPath(pathInZooKeeper);
    +
    +		return (StateHandle<T>) InstantiationUtil.deserializeObject(data, ClassLoader
    +				.getSystemClassLoader());
    +	}
    +
    +	/**
    +	 * Gets all available state handles from ZooKeeper.
    +	 *
    +	 * @return All state handles from ZooKeeper.
    +	 * @throws ConcurrentModificationException
    +	 */
    +	@SuppressWarnings("unchecked")
    +	public List<ZooKeeperStateHandle<T>> getAll() throws Exception {
    +		// Initial cVersion (number of changes to the children of this node)
    +		int initialCVersion = client.checkExists().forPath("/").getCversion();
    +
    +		List<String> children = client.getChildren().forPath("/");
    +
    +		final List<ZooKeeperStateHandle<T>> stateHandles = new ArrayList<>(children.size());
    +
    +		for (String path : children) {
    +			path = "/" + path;
    +
    +			try {
    +				final StateHandle<T> stateHandle = get(path);
    +				stateHandles.add(new ZooKeeperStateHandle(stateHandle, path));
    +			}
    +			catch (KeeperException.NoNodeException e) {
    +				throw new ConcurrentModificationException("Modification during getAll()", e);
    +			}
    +		}
    +
    +		verifyExpectedCVersion(initialCVersion, "/", "Modification during getAll()");
    +
    +		return stateHandles;
    +	}
    +
    +	/**
    +	 * Gets all available state handles from ZooKeeper sorted by name (ascending).
    +	 *
    +	 * @return All state handles in ZooKeeper.
    +	 */
    +	@SuppressWarnings("unchecked")
    +	public List<ZooKeeperStateHandle<T>> getAllSortedByName() throws Exception
{
    +		// Initial cVersion (number of changes to the children of this node)
    +		int initialCVersion = client.checkExists().forPath("/").getCversion();
    +
    +		List<String> children = ZKPaths.getSortedChildren(
    +				client.getZookeeperClient().getZooKeeper(),
    +				ZKPaths.fixForNamespace(client.getNamespace(), "/"));
    +
    +		final List<ZooKeeperStateHandle<T>> stateHandles = new ArrayList<>(children.size());
    +
    +		for (String path : children) {
    +			path = "/" + path;
    +			try {
    +				final StateHandle<T> stateHandle = get(path);
    +				stateHandles.add(new ZooKeeperStateHandle(stateHandle, path));
    +			}
    +			catch (KeeperException.NoNodeException e) {
    +				throw new ConcurrentModificationException("Modification during getAllSortedByName()",
e);
    +			}
    +		}
    +
    +		verifyExpectedCVersion(initialCVersion, "/", "Modification during getAllSortedByName()");
    +
    +		return stateHandles;
    +	}
    +
    +	/**
    +	 * Removes a state handle from ZooKeeper.
    +	 *
    +	 * <p><stong>Important</stong>: this does not discard the state handle.
If you want to
    +	 * discard the state handle call {@link #discard(String)}.
    +	 *
    +	 * @param pathInZooKeeper Path of state handle to remove (expected to start with a '/')
    +	 * @throws Exception
    +	 */
    +	public void remove(String pathInZooKeeper) throws Exception {
    +		checkNotNull(pathInZooKeeper, "Path in ZooKeeper");
    +
    +		client
    +				.delete()
    +				.deletingChildrenIfNeeded()
    +				.forPath(pathInZooKeeper);
    --- End diff --
    
    Resolved


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