org.apache.spark.shuffle.api.ShufflePartitionWriter Maven / Gradle / Ivy
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* 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.spark.shuffle.api;
import java.io.IOException;
import java.util.Optional;
import java.io.OutputStream;
import org.apache.spark.annotation.Private;
/**
* :: Private ::
* An interface for opening streams to persist partition bytes to a backing data store.
*
* This writer stores bytes for one (mapper, reducer) pair, corresponding to one shuffle
* block.
*
* @since 3.0.0
*/
@Private
public interface ShufflePartitionWriter {
/**
* Open and return an {@link OutputStream} that can write bytes to the underlying
* data store.
*
* This method will only be called once on this partition writer in the map task, to write the
* bytes to the partition. The output stream will only be used to write the bytes for this
* partition. The map task closes this output stream upon writing all the bytes for this
* block, or if the write fails for any reason.
*
* Implementations that intend on combining the bytes for all the partitions written by this
* map task should reuse the same OutputStream instance across all the partition writers provided
* by the parent {@link ShuffleMapOutputWriter}. If one does so, ensure that
* {@link OutputStream#close()} does not close the resource, since it will be reused across
* partition writes. The underlying resources should be cleaned up in
* {@link ShuffleMapOutputWriter#commitAllPartitions()} and
* {@link ShuffleMapOutputWriter#abort(Throwable)}.
*/
OutputStream openStream() throws IOException;
/**
* Opens and returns a {@link WritableByteChannelWrapper} for transferring bytes from
* input byte channels to the underlying shuffle data store.
*
* This method will only be called once on this partition writer in the map task, to write the
* bytes to the partition. The channel will only be used to write the bytes for this
* partition. The map task closes this channel upon writing all the bytes for this
* block, or if the write fails for any reason.
*
* Implementations that intend on combining the bytes for all the partitions written by this
* map task should reuse the same channel instance across all the partition writers provided
* by the parent {@link ShuffleMapOutputWriter}. If one does so, ensure that
* {@link WritableByteChannelWrapper#close()} does not close the resource, since the channel
* will be reused across partition writes. The underlying resources should be cleaned up in
* {@link ShuffleMapOutputWriter#commitAllPartitions()} and
* {@link ShuffleMapOutputWriter#abort(Throwable)}.
*
* This method is primarily for advanced optimizations where bytes can be copied from the input
* spill files to the output channel without copying data into memory. If such optimizations are
* not supported, the implementation should return {@link Optional#empty()}. By default, the
* implementation returns {@link Optional#empty()}.
*
* Note that the returned {@link WritableByteChannelWrapper} itself is closed, but not the
* underlying channel that is returned by {@link WritableByteChannelWrapper#channel()}. Ensure
* that the underlying channel is cleaned up in {@link WritableByteChannelWrapper#close()},
* {@link ShuffleMapOutputWriter#commitAllPartitions()}, or
* {@link ShuffleMapOutputWriter#abort(Throwable)}.
*/
default Optional openChannelWrapper() throws IOException {
return Optional.empty();
}
/**
* Returns the number of bytes written either by this writer's output stream opened by
* {@link #openStream()} or the byte channel opened by {@link #openChannelWrapper()}.
*
* This can be different from the number of bytes given by the caller. For example, the
* stream might compress or encrypt the bytes before persisting the data to the backing
* data store.
*/
long getNumBytesWritten();
}