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From fhue...@apache.org
Subject [41/51] [abbrv] [partial] flink git commit: [FLINK-4676] [connectors] Merge batch and streaming connectors into common Maven module.
Date Fri, 02 Dec 2016 13:35:31 GMT
http://git-wip-us.apache.org/repos/asf/flink/blob/de4fe3b7/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/RollingSink.java
----------------------------------------------------------------------
diff --git a/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/RollingSink.java b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/RollingSink.java
new file mode 100644
index 0000000..fc4a35e
--- /dev/null
+++ b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/RollingSink.java
@@ -0,0 +1,916 @@
+/*
+ * 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.streaming.connectors.fs;
+
+import org.apache.commons.lang3.time.StopWatch;
+import org.apache.flink.api.common.ExecutionConfig;
+import org.apache.flink.api.common.state.ListState;
+import org.apache.flink.api.common.state.OperatorStateStore;
+import org.apache.flink.api.common.typeinfo.TypeInformation;
+import org.apache.flink.api.java.typeutils.InputTypeConfigurable;
+import org.apache.flink.configuration.Configuration;
+import org.apache.flink.runtime.fs.hdfs.HadoopFileSystem;
+import org.apache.flink.runtime.state.CheckpointListener;
+import org.apache.flink.runtime.state.FunctionInitializationContext;
+import org.apache.flink.runtime.state.FunctionSnapshotContext;
+import org.apache.flink.streaming.api.checkpoint.CheckpointedFunction;
+import org.apache.flink.streaming.api.functions.sink.RichSinkFunction;
+import org.apache.flink.streaming.connectors.fs.bucketing.BucketingSink;
+import org.apache.flink.util.Preconditions;
+import org.apache.hadoop.fs.FSDataOutputStream;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.hdfs.DistributedFileSystem;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.io.Serializable;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.UUID;
+
+/**
+ * Sink that emits its input elements to rolling {@link org.apache.hadoop.fs.FileSystem} files. This
+ * is integrated with the checkpointing mechanism to provide exactly once semantics.
+ *
+ * <p>
+ * When creating the sink a {@code basePath} must be specified. The base directory contains
+ * one directory for every bucket. The bucket directories themselves contain several part files.
+ * These contain the actual written data.
+ *
+ * <p>
+ * The sink uses a {@link Bucketer} to determine the name of bucket directories inside the
+ * base directory. Whenever the {@code Bucketer} returns a different directory name than
+ * it returned before the sink will close the current part files inside that bucket
+ * and start the new bucket directory. The default bucketer is a {@link DateTimeBucketer} with
+ * date format string {@code ""yyyy-MM-dd--HH"}. You can specify a custom {@code Bucketer}
+ * using {@link #setBucketer(Bucketer)}. For example, use
+ * {@link NonRollingBucketer} if you don't want to have
+ * buckets but still write part files in a fault-tolerant way.
+ *
+ * <p>
+ * The filenames of the part files contain the part prefix, the parallel subtask index of the sink
+ * and a rolling counter, for example {@code "part-1-17"}. Per default the part prefix is
+ * {@code "part"} but this can be
+ * configured using {@link #setPartPrefix(String)}. When a part file becomes bigger
+ * than the batch size the current part file is closed, the part counter is increased and
+ * a new part file is created. The batch size defaults to {@code 384MB}, this can be configured
+ * using {@link #setBatchSize(long)}.
+ *
+ * <p>
+ * Part files can be in one of three states: in-progress, pending or finished. The reason for this
+ * is how the sink works together with the checkpointing mechanism to provide exactly-once semantics
+ * and fault-tolerance. The part file that is currently being written to is in-progress. Once
+ * a part file is closed for writing it becomes pending. When a checkpoint is successful the
+ * currently pending files will be moved to finished. If a failure occurs the pending files
+ * will be deleted to reset state to the last checkpoint. The data in in-progress files will
+ * also have to be rolled back. If the {@code FileSystem} supports the {@code truncate} call
+ * this will be used to reset the file back to a previous state. If not, a special file
+ * with the same name as the part file and the suffix {@code ".valid-length"} will be written
+ * that contains the length up to which the file contains valid data. When reading the file
+ * it must be ensured that it is only read up to that point. The prefixes and suffixes for
+ * the different file states and valid-length files can be configured, for example with
+ * {@link #setPendingSuffix(String)}.
+ *
+ * <p>
+ * Note: If checkpointing is not enabled the pending files will never be moved to the finished state.
+ * In that case, the pending suffix/prefix can be set to {@code ""} to make the sink work
+ * in a non-fault-tolerant way but still provide output without prefixes and suffixes.
+ *
+ * <p>
+ * The part files are written using an instance of {@link Writer}. By default
+ * {@link org.apache.flink.streaming.connectors.fs.StringWriter} is used, which writes the result
+ * of {@code toString()} for every element. Separated by newlines. You can configure the writer
+ * using {@link #setWriter(Writer)}. For example,
+ * {@link org.apache.flink.streaming.connectors.fs.SequenceFileWriter} can be used to write
+ * Hadoop {@code SequenceFiles}.
+ *
+ * <p>
+ * Example:
+ *
+ * <pre>{@code
+ *     new RollingSink<Tuple2<IntWritable, Text>>(outPath)
+ *         .setWriter(new SequenceFileWriter<IntWritable, Text>())
+ *         .setBucketer(new DateTimeBucketer("yyyy-MM-dd--HHmm")
+ * }</pre>
+ *
+ * This will create a sink that writes to {@code SequenceFiles} and rolls every minute.
+ *
+ * @see DateTimeBucketer
+ * @see StringWriter
+ * @see SequenceFileWriter
+ *
+ * @param <T> Type of the elements emitted by this sink
+ *
+ * @deprecated use {@link BucketingSink} instead.
+ */
+@Deprecated
+public class RollingSink<T> extends RichSinkFunction<T>
+		implements InputTypeConfigurable, CheckpointedFunction, CheckpointListener {
+
+	private static final long serialVersionUID = 1L;
+
+	private static Logger LOG = LoggerFactory.getLogger(RollingSink.class);
+
+
+	// --------------------------------------------------------------------------------------------
+	//  User configuration values
+	// --------------------------------------------------------------------------------------------
+	// These are initialized with some defaults but are meant to be changeable by the user
+
+	/**
+	 * The default maximum size of part files (currently {@code 384 MB}).
+	 */
+	private final long DEFAULT_BATCH_SIZE = 1024L * 1024L * 384L;
+
+	/**
+	 * This is used for part files that we are writing to but which where not yet confirmed
+	 * by a checkpoint.
+	 */
+	private final String DEFAULT_IN_PROGRESS_SUFFIX = ".in-progress";
+
+	/**
+	 * See above, but for prefix
+	 */
+	private final String DEFAULT_IN_PROGRESS_PREFIX = "_";
+
+	/**
+	 * This is used for part files that we are not writing to but which are not yet confirmed by
+	 * checkpoint.
+	 */
+	private final String DEFAULT_PENDING_SUFFIX = ".pending";
+
+	/**
+	 * See above, but for prefix.
+	 */
+	private final String DEFAULT_PENDING_PREFIX = "_";
+
+	/**
+	 * When truncate() is not supported on the used FileSystem we instead write a
+	 * file along the part file with this ending that contains the length up to which
+	 * the part file is valid.
+	 */
+	private final String DEFAULT_VALID_SUFFIX = ".valid-length";
+
+	/**
+	 * See above, but for prefix.
+	 */
+	private final String DEFAULT_VALID_PREFIX = "_";
+
+	/**
+	 * The default prefix for part files.
+	 */
+	private final String DEFAULT_PART_REFIX = "part";
+
+	/**
+	 * The default timeout for asynchronous operations such as recoverLease and truncate. In
+	 * milliseconds.
+	 */
+	private final long DEFAULT_ASYNC_TIMEOUT_MS = 60 * 1000;
+
+
+	/**
+	 * The base {@code Path} that stores all bucket directories.
+	 */
+	private final String basePath;
+
+	/**
+	 * The {@code Bucketer} that is used to determine the path of bucket directories.
+	 */
+	private Bucketer bucketer;
+
+	/**
+	 * We have a template and call duplicate() for each parallel writer in open() to get the actual
+	 * writer that is used for the part files.
+	 */
+	private Writer<T> writerTemplate;
+
+	/**
+	 * The actual writer that we user for writing the part files.
+	 */
+	private Writer<T> writer;
+
+	/**
+	 * Maximum size of part files. If files exceed this we close and create a new one in the same
+	 * bucket directory.
+	 */
+	private long batchSize;
+
+	// These are the actually configured prefixes/suffixes
+	private String inProgressSuffix = DEFAULT_IN_PROGRESS_SUFFIX;
+	private String inProgressPrefix = DEFAULT_IN_PROGRESS_PREFIX;
+
+	private String pendingSuffix = DEFAULT_PENDING_SUFFIX;
+	private String pendingPrefix = DEFAULT_PENDING_PREFIX;
+
+	private String validLengthSuffix = DEFAULT_VALID_SUFFIX;
+	private String validLengthPrefix= DEFAULT_VALID_PREFIX;
+
+	private String partPrefix = DEFAULT_PART_REFIX;
+
+	/**
+	 * The timeout for asynchronous operations such as recoverLease and truncate. In
+	 * milliseconds.
+	 */
+	private long asyncTimeout = DEFAULT_ASYNC_TIMEOUT_MS;
+
+	// --------------------------------------------------------------------------------------------
+	//  Internal fields (not configurable by user)
+	// --------------------------------------------------------------------------------------------
+
+
+	/**
+	 * The part file that we are currently writing to.
+	 */
+	private transient Path currentPartPath;
+
+	/**
+	 * The bucket directory that we are currently filling.
+	 */
+	private transient Path currentBucketDirectory;
+
+	/**
+	 * For counting the part files inside a bucket directory. Part files follow the patter
+	 * {@code "{part-prefix}-{subtask}-{count}"}. When creating new part files we increase the counter.
+	 */
+	private transient int partCounter;
+
+	/**
+	 * Tracks if the writer is currently opened or closed.
+	 */
+	private transient boolean isWriterOpen;
+
+	/**
+	 * We use reflection to get the .truncate() method, this is only available starting with
+	 * Hadoop 2.7
+	 */
+	private transient Method refTruncate;
+
+	/**
+	 * The state object that is handled by flink from snapshot/restore. In there we store the
+	 * current part file path, the valid length of the in-progress files and pending part files.
+	 */
+	private transient BucketState bucketState;
+
+	private transient ListState<BucketState> restoredBucketStates;
+
+	/**
+	 * User-defined FileSystem parameters.
+     */
+	private Configuration fsConfig;
+
+	/**
+	 * The FileSystem reference.
+	 */
+	private transient FileSystem fs;
+	/**
+	 * Creates a new {@code RollingSink} that writes files to the given base directory.
+	 *
+	 * <p>
+	 * This uses a{@link DateTimeBucketer} as bucketer and a {@link StringWriter} has writer.
+	 * The maximum bucket size is set to 384 MB.
+	 *
+	 * @param basePath The directory to which to write the bucket files.
+	 */
+	public RollingSink(String basePath) {
+		this.basePath = basePath;
+		this.bucketer = new DateTimeBucketer();
+		this.batchSize = DEFAULT_BATCH_SIZE;
+		this.writerTemplate = new StringWriter<>();
+	}
+
+	/**
+	 * Specify a custom {@code Configuration} that will be used when creating
+	 * the {@link FileSystem} for writing.
+	 */
+	public RollingSink<T> setFSConfig(Configuration config) {
+		this.fsConfig = new Configuration();
+		fsConfig.addAll(config);
+		return this;
+	}
+
+	/**
+	 * Specify a custom {@code Configuration} that will be used when creating
+	 * the {@link FileSystem} for writing.
+	 */
+	public RollingSink<T> setFSConfig(org.apache.hadoop.conf.Configuration config) {
+		this.fsConfig = new Configuration();
+		for(Map.Entry<String, String> entry : config) {
+			fsConfig.setString(entry.getKey(), entry.getValue());
+		}
+		return this;
+	}
+
+	@Override
+	@SuppressWarnings("unchecked")
+	public void setInputType(TypeInformation<?> type, ExecutionConfig executionConfig) {
+		if (this.writerTemplate instanceof InputTypeConfigurable) {
+			((InputTypeConfigurable) writerTemplate).setInputType(type, executionConfig);
+		}
+	}
+
+	@Override
+	public void initializeState(FunctionInitializationContext context) throws Exception {
+		Preconditions.checkArgument(this.restoredBucketStates == null,
+			"The " + getClass().getSimpleName() + " has already been initialized.");
+
+		initFileSystem();
+
+		if (this.refTruncate == null) {
+			this.refTruncate = reflectTruncate(fs);
+		}
+
+		OperatorStateStore stateStore = context.getOperatorStateStore();
+		restoredBucketStates = stateStore.getSerializableListState("rolling-states");
+
+		int subtaskIndex = getRuntimeContext().getIndexOfThisSubtask();
+		if (context.isRestored()) {
+			LOG.info("Restoring state for the {} (taskIdx={}).", getClass().getSimpleName(), subtaskIndex);
+
+			for (BucketState bucketState : restoredBucketStates.get()) {
+				handleRestoredBucketState(bucketState);
+			}
+
+			if (LOG.isDebugEnabled()) {
+				LOG.debug("{} (taskIdx= {}) restored {}", getClass().getSimpleName(), subtaskIndex, bucketState);
+			}
+		} else {
+			LOG.info("No state to restore for the {} (taskIdx= {}).", getClass().getSimpleName(), subtaskIndex);
+		}
+	}
+
+	@Override
+	public void open(Configuration parameters) throws Exception {
+		super.open(parameters);
+
+		partCounter = 0;
+
+		this.writer = writerTemplate.duplicate();
+
+		bucketState = new BucketState();
+	}
+
+	/**
+	 * Create a file system with the user-defined hdfs config
+	 * @throws IOException
+	 */
+	private void initFileSystem() throws IOException {
+		if (fs != null) {
+			return;
+		}
+		org.apache.hadoop.conf.Configuration hadoopConf = HadoopFileSystem.getHadoopConfiguration();
+		if (fsConfig != null) {
+			String disableCacheName = String.format("fs.%s.impl.disable.cache", new Path(basePath).toUri().getScheme());
+			hadoopConf.setBoolean(disableCacheName, true);
+			for (String key : fsConfig.keySet()) {
+				hadoopConf.set(key, fsConfig.getString(key, null));
+			}
+		}
+
+		fs = new Path(basePath).getFileSystem(hadoopConf);
+	}
+
+	@Override
+	public void close() throws Exception {
+		closeCurrentPartFile();
+	}
+
+	@Override
+	public void invoke(T value) throws Exception {
+		if (shouldRoll()) {
+			openNewPartFile();
+		}
+		writer.write(value);
+	}
+
+	/**
+	 * Determines whether we should change the bucket file we are writing to.
+	 *
+	 * <p>
+	 * This will roll if no file was created yet, if the file size is larger than the specified size
+	 * or if the {@code Bucketer} determines that we should roll.
+	 */
+	private boolean shouldRoll() throws IOException {
+		boolean shouldRoll = false;
+		int subtaskIndex = getRuntimeContext().getIndexOfThisSubtask();
+		if (!isWriterOpen) {
+			shouldRoll = true;
+			LOG.debug("RollingSink {} starting new initial bucket. ", subtaskIndex);
+		}
+		if (bucketer.shouldStartNewBucket(new Path(basePath), currentBucketDirectory)) {
+			shouldRoll = true;
+			LOG.debug("RollingSink {} starting new bucket because {} said we should. ", subtaskIndex, bucketer);
+			// we will retrieve a new bucket base path in openNewPartFile so reset the part counter
+			partCounter = 0;
+		}
+		if (isWriterOpen) {
+			long writePosition = writer.getPos();
+			if (isWriterOpen && writePosition > batchSize) {
+				shouldRoll = true;
+				LOG.debug(
+						"RollingSink {} starting new bucket because file position {} is above batch size {}.",
+						subtaskIndex,
+						writePosition,
+						batchSize);
+			}
+		}
+		return shouldRoll;
+	}
+
+	/**
+	 * Opens a new part file.
+	 *
+	 * <p>
+	 * This closes the old bucket file and retrieves a new bucket path from the {@code Bucketer}.
+	 */
+	private void openNewPartFile() throws Exception {
+		closeCurrentPartFile();
+
+		Path newBucketDirectory = bucketer.getNextBucketPath(new Path(basePath));
+
+		if (!newBucketDirectory.equals(currentBucketDirectory)) {
+			currentBucketDirectory = newBucketDirectory;
+			try {
+				if (fs.mkdirs(currentBucketDirectory)) {
+					LOG.debug("Created new bucket directory: {}", currentBucketDirectory);
+				}
+			} catch (IOException e) {
+				throw new RuntimeException("Could not create base path for new rolling file.", e);
+			}
+		}
+
+		int subtaskIndex = getRuntimeContext().getIndexOfThisSubtask();
+		currentPartPath = new Path(currentBucketDirectory, partPrefix + "-" + subtaskIndex + "-" + partCounter);
+
+		// This should work since there is only one parallel subtask that tries names with
+		// our subtask id. Otherwise we would run into concurrency issues here.
+		while (fs.exists(currentPartPath) ||
+				fs.exists(getPendingPathFor(currentPartPath)) ||
+				fs.exists(getInProgressPathFor(currentPartPath))) {
+			partCounter++;
+			currentPartPath = new Path(currentBucketDirectory, partPrefix + "-" + subtaskIndex + "-" + partCounter);
+		}
+
+		// increase, so we don't have to check for this name next time
+		partCounter++;
+
+		LOG.debug("Next part path is {}", currentPartPath.toString());
+
+		Path inProgressPath = getInProgressPathFor(currentPartPath);
+		writer.open(fs, inProgressPath);
+		isWriterOpen = true;
+	}
+
+	private Path getPendingPathFor(Path path) {
+		return new Path(path.getParent(), pendingPrefix + path.getName()).suffix(pendingSuffix);
+	}
+
+	private Path getInProgressPathFor(Path path) {
+		return new Path(path.getParent(), inProgressPrefix + path.getName()).suffix(inProgressSuffix);
+	}
+
+	private Path getValidLengthPathFor(Path path) {
+		return new Path(path.getParent(), validLengthPrefix + path.getName()).suffix(validLengthSuffix);
+	}
+
+	/**
+	 * Closes the current part file.
+	 *
+	 * <p>
+	 * This moves the current in-progress part file to a pending file and adds it to the list
+	 * of pending files in our bucket state.
+	 */
+	private void closeCurrentPartFile() throws Exception {
+		if (isWriterOpen) {
+			writer.close();
+			isWriterOpen = false;
+		}
+
+		if (currentPartPath != null) {
+			Path inProgressPath = getInProgressPathFor(currentPartPath);
+			Path pendingPath = getPendingPathFor(currentPartPath);
+			fs.rename(inProgressPath, pendingPath);
+			LOG.debug("Moving in-progress bucket {} to pending file {}", inProgressPath, pendingPath);
+			this.bucketState.pendingFiles.add(currentPartPath.toString());
+		}
+	}
+
+	/**
+	 * Gets the truncate() call using reflection.
+	 * <p>
+	 * <b>NOTE: </b>This code comes from Flume
+	 */
+	private Method reflectTruncate(FileSystem fs) {
+		Method m = null;
+		if (fs != null) {
+			Class<?> fsClass = fs.getClass();
+			try {
+				m = fsClass.getMethod("truncate", Path.class, long.class);
+			} catch (NoSuchMethodException ex) {
+				LOG.debug("Truncate not found. Will write a file with suffix '{}' " +
+						" and prefix '{}' to specify how many bytes in a bucket are valid.", validLengthSuffix, validLengthPrefix);
+				return null;
+			}
+
+			// verify that truncate actually works
+			FSDataOutputStream outputStream;
+			Path testPath = new Path(UUID.randomUUID().toString());
+			try {
+				outputStream = fs.create(testPath);
+				outputStream.writeUTF("hello");
+				outputStream.close();
+			} catch (IOException e) {
+				LOG.error("Could not create file for checking if truncate works.", e);
+				throw new RuntimeException("Could not create file for checking if truncate works.", e);
+			}
+
+			try {
+				m.invoke(fs, testPath, 2);
+			} catch (IllegalAccessException | InvocationTargetException e) {
+				LOG.debug("Truncate is not supported.", e);
+				m = null;
+			}
+
+			try {
+				fs.delete(testPath, false);
+			} catch (IOException e) {
+				LOG.error("Could not delete truncate test file.", e);
+				throw new RuntimeException("Could not delete truncate test file.", e);
+			}
+		}
+		return m;
+	}
+
+	@Override
+	public void notifyCheckpointComplete(long checkpointId) throws Exception {
+		synchronized (bucketState.pendingFilesPerCheckpoint) {
+			Iterator<Map.Entry<Long, List<String>>> pendingCheckpointsIt =
+				bucketState.pendingFilesPerCheckpoint.entrySet().iterator();
+
+			while (pendingCheckpointsIt.hasNext()) {
+				Map.Entry<Long, List<String>> entry = pendingCheckpointsIt.next();
+				Long pastCheckpointId = entry.getKey();
+
+				if (pastCheckpointId <= checkpointId) {
+					LOG.debug("Moving pending files to final location for checkpoint {}", pastCheckpointId);
+					// All the pending files are buckets that have been completed but are waiting to be renamed
+					// to their final name
+					for (String filename : entry.getValue()) {
+						Path finalPath = new Path(filename);
+						Path pendingPath = getPendingPathFor(finalPath);
+
+						fs.rename(pendingPath, finalPath);
+						LOG.debug("Moving pending file {} to final location after complete checkpoint {}.",
+								pendingPath, pastCheckpointId);
+					}
+					pendingCheckpointsIt.remove();
+				}
+			}
+		}
+	}
+
+	@Override
+	public void snapshotState(FunctionSnapshotContext context) throws Exception {
+		Preconditions.checkNotNull(restoredBucketStates,
+			"The " + getClass().getSimpleName() + " has not been properly initialized.");
+
+		int subtaskIdx = getRuntimeContext().getIndexOfThisSubtask();
+		
+		if (isWriterOpen) {
+			bucketState.currentFile = currentPartPath.toString();
+			bucketState.currentFileValidLength = writer.flush();
+		}
+
+		synchronized (bucketState.pendingFilesPerCheckpoint) {
+			bucketState.pendingFilesPerCheckpoint.put(context.getCheckpointId(), bucketState.pendingFiles);
+		}
+		bucketState.pendingFiles = new ArrayList<>();
+
+		restoredBucketStates.clear();
+		restoredBucketStates.add(bucketState);
+
+		if (LOG.isDebugEnabled()) {
+			LOG.debug("{} (taskIdx={}) checkpointed {}.", getClass().getSimpleName(), subtaskIdx, bucketState);
+		}
+	}
+
+	private void handleRestoredBucketState(BucketState bucketState) {
+		// we can clean all the pending files since they were renamed to
+		// final files after this checkpoint was successful
+		// (we re-start from the last **successful** checkpoint)
+		bucketState.pendingFiles.clear();
+
+		if (bucketState.currentFile != null) {
+			// We were writing to a file when the last checkpoint occurred. This file can either
+			// be still in-progress or became a pending file at some point after the checkpoint.
+			// Either way, we have to truncate it back to a valid state (or write a .valid-length
+			// file that specifies up to which length it is valid) and rename it to the final name
+			// before starting a new bucket file.
+			Path partPath = new Path(bucketState.currentFile);
+			try {
+				Path partPendingPath = getPendingPathFor(partPath);
+				Path partInProgressPath = getInProgressPathFor(partPath);
+
+				if (fs.exists(partPendingPath)) {
+					LOG.debug("In-progress file {} has been moved to pending after checkpoint, moving to final location.", partPath);
+					// has been moved to pending in the mean time, rename to final location
+					fs.rename(partPendingPath, partPath);
+				} else if (fs.exists(partInProgressPath)) {
+					LOG.debug("In-progress file {} is still in-progress, moving to final location.", partPath);
+					// it was still in progress, rename to final path
+					fs.rename(partInProgressPath, partPath);
+				} else if (fs.exists(partPath)) {
+					LOG.debug("In-Progress file {} was already moved to final location {}.", bucketState.currentFile, partPath);
+				} else {
+					LOG.debug("In-Progress file {} was neither moved to pending nor is still in progress. Possibly, " +
+							"it was moved to final location by a previous snapshot restore", bucketState.currentFile);
+				}
+
+				if (this.refTruncate == null) {
+					this.refTruncate = reflectTruncate(fs);
+				}
+
+				// truncate it or write a ".valid-length" file to specify up to which point it is valid
+				if (refTruncate != null) {
+					LOG.debug("Truncating {} to valid length {}", partPath, bucketState.currentFileValidLength);
+					// some-one else might still hold the lease from a previous try, we are
+					// recovering, after all ...
+					if (fs instanceof DistributedFileSystem) {
+						DistributedFileSystem dfs = (DistributedFileSystem) fs;
+						LOG.debug("Trying to recover file lease {}", partPath);
+						dfs.recoverLease(partPath);
+						boolean isclosed= dfs.isFileClosed(partPath);
+						StopWatch sw = new StopWatch();
+						sw.start();
+						while(!isclosed) {
+							if(sw.getTime() > asyncTimeout) {
+								break;
+							}
+							try {
+								Thread.sleep(500);
+							} catch (InterruptedException e1) {
+								// ignore it
+							}
+							isclosed = dfs.isFileClosed(partPath);
+						}
+					}
+					Boolean truncated = (Boolean) refTruncate.invoke(fs, partPath, bucketState.currentFileValidLength);
+					if (!truncated) {
+						LOG.debug("Truncate did not immediately complete for {}, waiting...", partPath);
+
+						// we must wait for the asynchronous truncate operation to complete
+						StopWatch sw = new StopWatch();
+						sw.start();
+						long newLen = fs.getFileStatus(partPath).getLen();
+						while(newLen != bucketState.currentFileValidLength) {
+							if(sw.getTime() > asyncTimeout) {
+								break;
+							}
+							try {
+								Thread.sleep(500);
+							} catch (InterruptedException e1) {
+								// ignore it
+							}
+							newLen = fs.getFileStatus(partPath).getLen();
+						}
+						if (newLen != bucketState.currentFileValidLength) {
+							throw new RuntimeException("Truncate did not truncate to right length. Should be " + bucketState.currentFileValidLength + " is " + newLen + ".");
+						}
+					}
+
+				} else {
+					LOG.debug("Writing valid-length file for {} to specify valid length {}", partPath, bucketState.currentFileValidLength);
+					Path validLengthFilePath = getValidLengthPathFor(partPath);
+					if (!fs.exists(validLengthFilePath)) {
+						FSDataOutputStream lengthFileOut = fs.create(validLengthFilePath);
+						lengthFileOut.writeUTF(Long.toString(bucketState.currentFileValidLength));
+						lengthFileOut.close();
+					}
+				}
+
+				// invalidate in the state object
+				bucketState.currentFile = null;
+				bucketState.currentFileValidLength = -1;
+				isWriterOpen = false;
+			} catch (IOException e) {
+				LOG.error("Error while restoring RollingSink state.", e);
+				throw new RuntimeException("Error while restoring RollingSink state.", e);
+			} catch (InvocationTargetException | IllegalAccessException e) {
+				LOG.error("Could not invoke truncate.", e);
+				throw new RuntimeException("Could not invoke truncate.", e);
+			}
+		}
+
+		// Move files that are confirmed by a checkpoint but did not get moved to final location
+		// because the checkpoint notification did not happen before a failure
+
+		Set<Long> pastCheckpointIds = bucketState.pendingFilesPerCheckpoint.keySet();
+		LOG.debug("Moving pending files to final location on restore.");
+		for (Long pastCheckpointId : pastCheckpointIds) {
+			// All the pending files are buckets that have been completed but are waiting to be renamed
+			// to their final name
+			for (String filename : bucketState.pendingFilesPerCheckpoint.get(pastCheckpointId)) {
+				Path finalPath = new Path(filename);
+				Path pendingPath = getPendingPathFor(finalPath);
+
+				try {
+					if (fs.exists(pendingPath)) {
+						LOG.debug("(RESTORE) Moving pending file {} to final location after complete checkpoint {}.", pendingPath, pastCheckpointId);
+						fs.rename(pendingPath, finalPath);
+					}
+				} catch (IOException e) {
+					LOG.error("(RESTORE) Error while renaming pending file {} to final path {}: {}", pendingPath, finalPath, e);
+					throw new RuntimeException("Error while renaming pending file " + pendingPath+ " to final path " + finalPath, e);
+				}
+			}
+		}
+
+		synchronized (bucketState.pendingFilesPerCheckpoint) {
+			bucketState.pendingFilesPerCheckpoint.clear();
+		}
+	}
+
+	// --------------------------------------------------------------------------------------------
+	//  Setters for User configuration values
+	// --------------------------------------------------------------------------------------------
+
+	/**
+	 * Sets the maximum bucket size in bytes.
+	 *
+	 * <p>
+	 * When a bucket part file becomes larger than this size a new bucket part file is started and
+	 * the old one is closed. The name of the bucket files depends on the {@link Bucketer}.
+	 *
+	 * @param batchSize The bucket part file size in bytes.
+	 */
+	public RollingSink<T> setBatchSize(long batchSize) {
+		this.batchSize = batchSize;
+		return this;
+	}
+
+	/**
+	 * Sets the {@link Bucketer} to use for determining the bucket files to write to.
+	 *
+	 * @param bucketer The bucketer to use.
+	 */
+	public RollingSink<T> setBucketer(Bucketer bucketer) {
+		this.bucketer = bucketer;
+		return this;
+	}
+
+	/**
+	 * Sets the {@link Writer} to be used for writing the incoming elements to bucket files.
+	 *
+	 * @param writer The {@code Writer} to use.
+	 */
+	public RollingSink<T> setWriter(Writer<T> writer) {
+		this.writerTemplate = writer;
+		return this;
+	}
+
+	/**
+	 * Sets the suffix of in-progress part files. The default is {@code "in-progress"}.
+	 */
+	public RollingSink<T> setInProgressSuffix(String inProgressSuffix) {
+		this.inProgressSuffix = inProgressSuffix;
+		return this;
+	}
+
+	/**
+	 * Sets the prefix of in-progress part files. The default is {@code "_"}.
+	 */
+	public RollingSink<T> setInProgressPrefix(String inProgressPrefix) {
+		this.inProgressPrefix = inProgressPrefix;
+		return this;
+	}
+
+	/**
+	 * Sets the suffix of pending part files. The default is {@code ".pending"}.
+	 */
+	public RollingSink<T> setPendingSuffix(String pendingSuffix) {
+		this.pendingSuffix = pendingSuffix;
+		return this;
+	}
+
+	/**
+	 * Sets the prefix of pending part files. The default is {@code "_"}.
+	 */
+	public RollingSink<T> setPendingPrefix(String pendingPrefix) {
+		this.pendingPrefix = pendingPrefix;
+		return this;
+	}
+
+	/**
+	 * Sets the suffix of valid-length files. The default is {@code ".valid-length"}.
+	 */
+	public RollingSink<T> setValidLengthSuffix(String validLengthSuffix) {
+		this.validLengthSuffix = validLengthSuffix;
+		return this;
+	}
+
+	/**
+	 * Sets the prefix of valid-length files. The default is {@code "_"}.
+	 */
+	public RollingSink<T> setValidLengthPrefix(String validLengthPrefix) {
+		this.validLengthPrefix = validLengthPrefix;
+		return this;
+	}
+
+	/**
+	 * Sets the prefix of part files.  The default is {@code "part"}.
+	 */
+	public RollingSink<T> setPartPrefix(String partPrefix) {
+		this.partPrefix = partPrefix;
+		return this;
+	}
+
+	/**
+	 * Disable cleanup of leftover in-progress/pending files when the sink is opened.
+	 *
+	 * <p>
+	 * This should only be disabled if using the sink without checkpoints, to not remove
+	 * the files already in the directory.
+	 *
+	 * @deprecated This option is deprecated and remains only for backwards compatibility.
+	 * We do not clean up lingering files anymore.
+	 */
+	@Deprecated
+	public RollingSink<T> disableCleanupOnOpen() {
+		return this;
+	}
+
+	/**
+	 * Sets the default timeout for asynchronous operations such as recoverLease and truncate.
+	 *
+	 * @param timeout The timeout, in milliseconds.
+	 */
+	public RollingSink<T> setAsyncTimeout(long timeout) {
+		this.asyncTimeout = timeout;
+		return this;
+	}
+
+	// --------------------------------------------------------------------------------------------
+	//  Internal Classes
+	// --------------------------------------------------------------------------------------------
+
+	/**
+	 * This is used for keeping track of the current in-progress files and files that we mark
+	 * for moving from pending to final location after we get a checkpoint-complete notification.
+	 */
+	static final class BucketState implements Serializable {
+		private static final long serialVersionUID = 1L;
+
+		/**
+		 * The file that was in-progress when the last checkpoint occurred.
+		 */
+		String currentFile;
+
+		/**
+		 * The valid length of the in-progress file at the time of the last checkpoint.
+		 */
+		long currentFileValidLength = -1;
+
+		/**
+		 * Pending files that accumulated since the last checkpoint.
+		 */
+		List<String> pendingFiles = new ArrayList<>();
+
+		/**
+		 * When doing a checkpoint we move the pending files since the last checkpoint to this map
+		 * with the id of the checkpoint. When we get the checkpoint-complete notification we move
+		 * pending files of completed checkpoints to their final location.
+		 */
+		final Map<Long, List<String>> pendingFilesPerCheckpoint = new HashMap<>();
+
+		@Override
+		public String toString() {
+			return
+				"In-progress=" + currentFile +
+				" validLength=" + currentFileValidLength +
+				" pendingForNextCheckpoint=" + pendingFiles +
+				" pendingForPrevCheckpoints=" + pendingFilesPerCheckpoint;
+		}
+	}
+}

http://git-wip-us.apache.org/repos/asf/flink/blob/de4fe3b7/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/SequenceFileWriter.java
----------------------------------------------------------------------
diff --git a/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/SequenceFileWriter.java b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/SequenceFileWriter.java
new file mode 100644
index 0000000..08c0d0a
--- /dev/null
+++ b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/SequenceFileWriter.java
@@ -0,0 +1,151 @@
+/**
+ * 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.streaming.connectors.fs;
+
+
+import org.apache.flink.api.common.ExecutionConfig;
+import org.apache.flink.api.common.typeinfo.TypeInformation;
+import org.apache.flink.api.java.tuple.Tuple2;
+import org.apache.flink.api.java.typeutils.InputTypeConfigurable;
+import org.apache.flink.api.java.typeutils.TupleTypeInfoBase;
+import org.apache.flink.runtime.fs.hdfs.HadoopFileSystem;
+import org.apache.flink.streaming.connectors.fs.bucketing.BucketingSink;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.io.SequenceFile;
+import org.apache.hadoop.io.Writable;
+import org.apache.hadoop.io.compress.CompressionCodec;
+import org.apache.hadoop.io.compress.CompressionCodecFactory;
+
+import java.io.IOException;
+
+/**
+ * A {@link Writer} that writes the bucket files as Hadoop {@link SequenceFile SequenceFiles}.
+ * The input to the {@link BucketingSink} must
+ * be a {@link org.apache.flink.api.java.tuple.Tuple2} of two Hadopo
+ * {@link org.apache.hadoop.io.Writable Writables}.
+ *
+ * @param <K> The type of the first tuple field.
+ * @param <V> The type of the second tuple field.
+ */
+public class SequenceFileWriter<K extends Writable, V extends Writable> extends StreamWriterBase<Tuple2<K, V>> implements InputTypeConfigurable {
+	private static final long serialVersionUID = 1L;
+
+	private final String compressionCodecName;
+
+	private SequenceFile.CompressionType compressionType;
+
+	private transient SequenceFile.Writer writer;
+
+	private Class<K> keyClass;
+
+	private Class<V> valueClass;
+
+	/**
+	 * Creates a new {@code SequenceFileWriter} that writes sequence files without compression.
+	 */
+	public SequenceFileWriter() {
+		this("None", SequenceFile.CompressionType.NONE);
+	}
+
+	/**
+	 * Creates a new {@code SequenceFileWriter} that writes sequence with the given
+	 * compression codec and compression type.
+	 *
+	 * @param compressionCodecName Name of a Hadoop Compression Codec.
+	 * @param compressionType The compression type to use.
+	 */
+	public SequenceFileWriter(String compressionCodecName,
+			SequenceFile.CompressionType compressionType) {
+		this.compressionCodecName = compressionCodecName;
+		this.compressionType = compressionType;
+	}
+
+	@Override
+	public void open(FileSystem fs, Path path) throws IOException {
+		super.open(fs, path);
+		if (keyClass == null) {
+			throw new IllegalStateException("Key Class has not been initialized.");
+		}
+		if (valueClass == null) {
+			throw new IllegalStateException("Value Class has not been initialized.");
+		}
+
+		CompressionCodec codec = null;
+		
+		Configuration conf = HadoopFileSystem.getHadoopConfiguration();
+
+		if (!compressionCodecName.equals("None")) {
+			CompressionCodecFactory codecFactory = new CompressionCodecFactory(conf);
+			codec = codecFactory.getCodecByName(compressionCodecName);
+			if (codec == null) {
+				throw new RuntimeException("Codec " + compressionCodecName + " not found.");
+			}
+		}
+
+		// the non-deprecated constructor syntax is only available in recent hadoop versions...
+		writer = SequenceFile.createWriter(conf,
+				getStream(),
+				keyClass,
+				valueClass,
+				compressionType,
+				codec);
+	}
+
+	@Override
+	public void close() throws IOException {
+		if (writer != null) {
+			writer.close();
+		}
+		super.close();
+	}
+
+	@Override
+	public void write(Tuple2<K, V> element) throws IOException {
+		getStream(); // Throws if the stream is not open
+		writer.append(element.f0, element.f1);
+	}
+
+	@Override
+	public void setInputType(TypeInformation<?> type, ExecutionConfig executionConfig) {
+		if (!type.isTupleType()) {
+			throw new IllegalArgumentException("Input TypeInformation is not a tuple type.");
+		}
+
+		TupleTypeInfoBase<?> tupleType = (TupleTypeInfoBase<?>) type;
+
+		if (tupleType.getArity() != 2) {
+			throw new IllegalArgumentException("Input TypeInformation must be a Tuple2 type.");
+		}
+
+		TypeInformation<K> keyType = tupleType.getTypeAt(0);
+		TypeInformation<V> valueType = tupleType.getTypeAt(1);
+
+		this.keyClass = keyType.getTypeClass();
+		this.valueClass = valueType.getTypeClass();
+	}
+
+	@Override
+	public Writer<Tuple2<K, V>> duplicate() {
+		SequenceFileWriter<K, V> result = new SequenceFileWriter<>(compressionCodecName, compressionType);
+		result.keyClass = keyClass;
+		result.valueClass = valueClass;
+		return result;
+	}
+}

http://git-wip-us.apache.org/repos/asf/flink/blob/de4fe3b7/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/StreamWriterBase.java
----------------------------------------------------------------------
diff --git a/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/StreamWriterBase.java b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/StreamWriterBase.java
new file mode 100644
index 0000000..140246f
--- /dev/null
+++ b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/StreamWriterBase.java
@@ -0,0 +1,152 @@
+/**
+ * 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.streaming.connectors.fs;
+
+import org.apache.flink.streaming.connectors.fs.bucketing.BucketingSink;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.fs.FSDataOutputStream;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+
+/**
+ * Base class for {@link Writer Writers} that write to a {@link FSDataOutputStream}.
+ */
+public abstract class StreamWriterBase<T> implements Writer<T> {
+
+	private static Logger LOG = LoggerFactory.getLogger(BucketingSink.class);
+
+	/**
+	 * The {@code FSDataOutputStream} for the current part file.
+	 */
+	private transient FSDataOutputStream outStream;
+
+	/**
+	 * We use reflection to get the hflush method or use sync as a fallback.
+	 * The idea for this and the code comes from the Flume HDFS Sink.
+	 */
+	private transient Method refHflushOrSync;
+
+	/**
+	 * Returns the current output stream, if the stream is open.
+	 */
+	protected FSDataOutputStream getStream() {
+		if (outStream == null) {
+			throw new IllegalStateException("Output stream has not been opened");
+		}
+		return outStream;
+	}
+
+	/**
+	 * If hflush is available in this version of HDFS, then this method calls
+	 * hflush, else it calls sync.
+	 * @param os - The stream to flush/sync
+	 * @throws java.io.IOException
+	 *
+	 * <p>
+	 * Note: This code comes from Flume
+	 */
+	protected void hflushOrSync(FSDataOutputStream os) throws IOException {
+		try {
+			// At this point the refHflushOrSync cannot be null,
+			// since register method would have thrown if it was.
+			this.refHflushOrSync.invoke(os);
+		} catch (InvocationTargetException e) {
+			String msg = "Error while trying to hflushOrSync!";
+			LOG.error(msg + " " + e.getCause());
+			Throwable cause = e.getCause();
+			if(cause != null && cause instanceof IOException) {
+				throw (IOException)cause;
+			}
+			throw new RuntimeException(msg, e);
+		} catch (Exception e) {
+			String msg = "Error while trying to hflushOrSync!";
+			LOG.error(msg + " " + e);
+			throw new RuntimeException(msg, e);
+		}
+	}
+
+	/**
+	 * Gets the hflush call using reflection. Fallback to sync if hflush is not available.
+	 *
+	 * <p>
+	 * Note: This code comes from Flume
+	 */
+	private Method reflectHflushOrSync(FSDataOutputStream os) {
+		Method m = null;
+		if(os != null) {
+			Class<?> fsDataOutputStreamClass = os.getClass();
+			try {
+				m = fsDataOutputStreamClass.getMethod("hflush");
+			} catch (NoSuchMethodException ex) {
+				LOG.debug("HFlush not found. Will use sync() instead");
+				try {
+					m = fsDataOutputStreamClass.getMethod("sync");
+				} catch (Exception ex1) {
+					String msg = "Neither hflush not sync were found. That seems to be " +
+							"a problem!";
+					LOG.error(msg);
+					throw new RuntimeException(msg, ex1);
+				}
+			}
+		}
+		return m;
+	}
+
+	@Override
+	public void open(FileSystem fs, Path path) throws IOException {
+		if (outStream != null) {
+			throw new IllegalStateException("Writer has already been opened");
+		}
+		outStream = fs.create(path, false);
+		if (refHflushOrSync == null) {
+			refHflushOrSync = reflectHflushOrSync(outStream);
+		}
+	}
+
+	@Override
+	public long flush() throws IOException {
+		if (outStream == null) {
+			throw new IllegalStateException("Writer is not open");
+		}
+		hflushOrSync(outStream);
+		return outStream.getPos();
+	}
+
+	@Override
+	public long getPos() throws IOException {
+		if (outStream == null) {
+			throw new IllegalStateException("Writer is not open");
+		}
+		return outStream.getPos();
+	}
+
+	@Override
+	public void close() throws IOException {
+		if (outStream != null) {
+			flush();
+			outStream.close();
+			outStream = null;
+		}
+	}
+
+}

http://git-wip-us.apache.org/repos/asf/flink/blob/de4fe3b7/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/StringWriter.java
----------------------------------------------------------------------
diff --git a/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/StringWriter.java b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/StringWriter.java
new file mode 100644
index 0000000..6568a86
--- /dev/null
+++ b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/StringWriter.java
@@ -0,0 +1,86 @@
+/**
+ * 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.streaming.connectors.fs;
+
+import org.apache.hadoop.fs.FSDataOutputStream;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+
+import java.io.IOException;
+import java.nio.charset.Charset;
+import java.nio.charset.IllegalCharsetNameException;
+import java.nio.charset.UnsupportedCharsetException;
+
+/**
+ * A {@link Writer} that uses {@code toString()} on the input elements and writes them to
+ * the output bucket file separated by newline.
+ *
+ * @param <T> The type of the elements that are being written by the sink.
+ */
+public class StringWriter<T> extends StreamWriterBase<T> {
+	private static final long serialVersionUID = 1L;
+
+	private String charsetName;
+
+	private transient Charset charset;
+
+	/**
+	 * Creates a new {@code StringWriter} that uses {@code "UTF-8"} charset to convert
+	 * strings to bytes.
+	 */
+	public StringWriter() {
+		this("UTF-8");
+	}
+
+	/**
+	 * Creates a new {@code StringWriter} that uses the given charset to convert
+	 * strings to bytes.
+	 *
+	 * @param charsetName Name of the charset to be used, must be valid input for {@code Charset.forName(charsetName)}
+	 */
+	public StringWriter(String charsetName) {
+		this.charsetName = charsetName;
+	}
+
+	@Override
+	public void open(FileSystem fs, Path path) throws IOException {
+		super.open(fs, path);
+
+		try {
+			this.charset = Charset.forName(charsetName);
+		}
+		catch (IllegalCharsetNameException e) {
+			throw new IOException("The charset " + charsetName + " is not valid.", e);
+		}
+		catch (UnsupportedCharsetException e) {
+			throw new IOException("The charset " + charsetName + " is not supported.", e);
+		}
+	}
+
+	@Override
+	public void write(T element) throws IOException {
+		FSDataOutputStream outputStream = getStream();
+		outputStream.write(element.toString().getBytes(charset));
+		outputStream.write('\n');
+	}
+
+	@Override
+	public Writer<T> duplicate() {
+		return new StringWriter<>();
+	}
+}

http://git-wip-us.apache.org/repos/asf/flink/blob/de4fe3b7/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/SystemClock.java
----------------------------------------------------------------------
diff --git a/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/SystemClock.java b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/SystemClock.java
new file mode 100644
index 0000000..41663df
--- /dev/null
+++ b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/SystemClock.java
@@ -0,0 +1,29 @@
+/**
+ * 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.streaming.connectors.fs;
+
+
+/**
+ * A {@link Clock} that uses {@code System.currentTimeMillis()} to determine the system time.
+ */
+public class SystemClock implements Clock {
+	@Override
+	public long currentTimeMillis() {
+		return System.currentTimeMillis();
+	}
+}

http://git-wip-us.apache.org/repos/asf/flink/blob/de4fe3b7/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/Writer.java
----------------------------------------------------------------------
diff --git a/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/Writer.java b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/Writer.java
new file mode 100644
index 0000000..c3b4cb6
--- /dev/null
+++ b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/Writer.java
@@ -0,0 +1,73 @@
+/**
+ * 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.streaming.connectors.fs;
+
+import org.apache.flink.streaming.connectors.fs.bucketing.BucketingSink;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+
+import java.io.IOException;
+import java.io.Serializable;
+
+/**
+ * An implementation of {@code Writer} is used in conjunction with a
+ * {@link BucketingSink} to perform the actual
+ * writing to the bucket files.
+ *
+ * @param <T> The type of the elements that are being written by the sink.
+ */
+public interface Writer<T> extends Serializable {
+
+	/**
+	 * Initializes the {@code Writer} for a newly opened bucket file.
+	 * Any internal per-bucket initialization should be performed here.
+	 *
+	 * @param fs The {@link org.apache.hadoop.fs.FileSystem} containing the newly opened file.
+	 * @param path The {@link org.apache.hadoop.fs.Path} of the newly opened file.
+	 */
+	void open(FileSystem fs, Path path) throws IOException;
+
+	/**
+	 * Flushes out any internally held data, and returns the offset that the file
+	 * must be truncated to at recovery.
+	 */
+	long flush() throws IOException;
+
+	/**
+	 * Retrieves the current position, and thus size, of the output file.
+	 */
+	long getPos() throws IOException;
+
+	/**
+	 * Closes the {@code Writer}. If the writer is already closed, no action will be
+	 * taken. The call should close all state related to the current output file,
+	 * including the output stream opened in {@code open}.
+	 */
+	void close() throws IOException ;
+
+	/**
+	 * Writes one element to the bucket file.
+	 */
+	void write(T element)throws IOException;
+
+	/**
+	 * Duplicates the {@code Writer}. This is used to get one {@code Writer} for each
+	 * parallel instance of the sink.
+	 */
+	Writer<T> duplicate();
+}

http://git-wip-us.apache.org/repos/asf/flink/blob/de4fe3b7/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/bucketing/BasePathBucketer.java
----------------------------------------------------------------------
diff --git a/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/bucketing/BasePathBucketer.java b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/bucketing/BasePathBucketer.java
new file mode 100644
index 0000000..0bf14b3
--- /dev/null
+++ b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/bucketing/BasePathBucketer.java
@@ -0,0 +1,39 @@
+/*
+ * 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.streaming.connectors.fs.bucketing;
+
+import org.apache.flink.streaming.connectors.fs.Clock;
+import org.apache.hadoop.fs.Path;
+
+/**
+ * A {@link Bucketer} that does not perform any
+ * bucketing of files. All files are written to the base path.
+ */
+public class BasePathBucketer<T> implements Bucketer<T> {
+	private static final long serialVersionUID = 1L;
+
+	@Override
+	public Path getBucketPath(Clock clock, Path basePath, T element) {
+		return basePath;
+	}
+
+	@Override
+	public String toString() {
+		return "BasePathBucketer";
+	}
+}

http://git-wip-us.apache.org/repos/asf/flink/blob/de4fe3b7/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/bucketing/Bucketer.java
----------------------------------------------------------------------
diff --git a/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/bucketing/Bucketer.java b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/bucketing/Bucketer.java
new file mode 100644
index 0000000..86aa9f3
--- /dev/null
+++ b/flink-connectors/flink-connector-filesystem/src/main/java/org/apache/flink/streaming/connectors/fs/bucketing/Bucketer.java
@@ -0,0 +1,47 @@
+/*
+ * 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.streaming.connectors.fs.bucketing;
+
+import org.apache.flink.streaming.connectors.fs.Clock;
+import org.apache.hadoop.fs.Path;
+
+import java.io.Serializable;
+
+/**
+ * A bucketer is used with a {@link BucketingSink}
+ * to put emitted elements into rolling files.
+ *
+ * <p>
+ * The {@code BucketingSink} can be writing to many buckets at a time, and it is responsible for managing
+ * a set of active buckets. Whenever a new element arrives it will ask the {@code Bucketer} for the bucket
+ * path the element should fall in. The {@code Bucketer} can, for example, determine buckets based on
+ * system time.
+ */
+public interface Bucketer<T> extends Serializable {
+	/**
+	 * Returns the {@link Path} of a bucket file.
+	 *
+	 * @param basePath The base path containing all the buckets.
+	 * @param element The current element being processed.
+	 *
+	 * @return The complete {@code Path} of the bucket which the provided element should fall in. This
+	 * should include the {@code basePath} and also the {@code subtaskIndex} to avoid clashes with
+	 * parallel sinks.
+	 */
+	Path getBucketPath(Clock clock, Path basePath, T element);
+}


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