org.apache.hadoop.hdfs.server.namenode.FSImageCompression Maven / Gradle / Ivy
/**
* 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.hadoop.hdfs.server.namenode;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.DataInput;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hdfs.DFSConfigKeys;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.compress.CompressionCodec;
import org.apache.hadoop.io.compress.CompressionCodecFactory;
/**
* Simple container class that handles support for compressed fsimage files.
*/
@InterfaceAudience.Private
@InterfaceStability.Evolving
public class FSImageCompression {
/** Codec to use to save or load image, or null if the image is not compressed */
private CompressionCodec imageCodec;
/**
* Create a "noop" compression - i.e. uncompressed
*/
private FSImageCompression() {
}
/**
* Create compression using a particular codec
*/
private FSImageCompression(CompressionCodec codec) {
imageCodec = codec;
}
public CompressionCodec getImageCodec() {
return imageCodec;
}
/**
* Create a "noop" compression - i.e. uncompressed
*/
static FSImageCompression createNoopCompression() {
return new FSImageCompression();
}
/**
* Create a compression instance based on the user's configuration in the given
* Configuration object.
* @throws IOException if the specified codec is not available.
*/
static FSImageCompression createCompression(Configuration conf)
throws IOException {
boolean compressImage = conf.getBoolean(
DFSConfigKeys.DFS_IMAGE_COMPRESS_KEY,
DFSConfigKeys.DFS_IMAGE_COMPRESS_DEFAULT);
if (!compressImage) {
return createNoopCompression();
}
String codecClassName = conf.get(
DFSConfigKeys.DFS_IMAGE_COMPRESSION_CODEC_KEY,
DFSConfigKeys.DFS_IMAGE_COMPRESSION_CODEC_DEFAULT);
return createCompression(conf, codecClassName);
}
/**
* Create a compression instance using the codec specified by
* codecClassName
*/
static FSImageCompression createCompression(Configuration conf,
String codecClassName)
throws IOException {
CompressionCodecFactory factory = new CompressionCodecFactory(conf);
CompressionCodec codec = factory.getCodecByClassName(codecClassName);
if (codec == null) {
throw new IOException("Not a supported codec: " + codecClassName);
}
return new FSImageCompression(codec);
}
/**
* Create a compression instance based on a header read from an input stream.
* @throws IOException if the specified codec is not available or the
* underlying IO fails.
*/
static FSImageCompression readCompressionHeader(
Configuration conf, DataInput in) throws IOException
{
boolean isCompressed = in.readBoolean();
if (!isCompressed) {
return createNoopCompression();
} else {
String codecClassName = Text.readString(in);
return createCompression(conf, codecClassName);
}
}
/**
* Unwrap a compressed input stream by wrapping it with a decompressor based
* on this codec. If this instance represents no compression, simply adds
* buffering to the input stream.
* @return a buffered stream that provides uncompressed data
* @throws IOException If the decompressor cannot be instantiated or an IO
* error occurs.
*/
DataInputStream unwrapInputStream(InputStream is) throws IOException {
if (imageCodec != null) {
return new DataInputStream(imageCodec.createInputStream(is));
} else {
return new DataInputStream(new BufferedInputStream(is));
}
}
/**
* Write out a header to the given stream that indicates the chosen
* compression codec, and return the same stream wrapped with that codec.
* If no codec is specified, simply adds buffering to the stream, so that
* the returned stream is always buffered.
*
* @param os The stream to write header to and wrap. This stream should
* be unbuffered.
* @return A stream wrapped with the specified compressor, or buffering
* if compression is not enabled.
* @throws IOException if an IO error occurs or the compressor cannot be
* instantiated
*/
DataOutputStream writeHeaderAndWrapStream(OutputStream os)
throws IOException {
DataOutputStream dos = new DataOutputStream(os);
dos.writeBoolean(imageCodec != null);
if (imageCodec != null) {
String codecClassName = imageCodec.getClass().getCanonicalName();
Text.writeString(dos, codecClassName);
return new DataOutputStream(imageCodec.createOutputStream(os));
} else {
// use a buffered output stream
return new DataOutputStream(new BufferedOutputStream(os));
}
}
@Override
public String toString() {
if (imageCodec != null) {
return "codec " + imageCodec.getClass().getCanonicalName();
} else {
return "no compression";
}
}
}