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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.parquet.bytes;
import static java.lang.Math.max;
import static java.lang.Math.pow;
import static java.lang.String.format;
import static org.apache.parquet.Preconditions.checkArgument;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.List;
import org.apache.parquet.OutputStreamCloseException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Similar to a {@link ByteArrayOutputStream}, but uses a different strategy for growing that does not involve copying.
* Where ByteArrayOutputStream is backed by a single array that "grows" by copying into a new larger array, this output
* stream grows by allocating a new array (slab) and adding it to a list of previous arrays.
*
* Each new slab is allocated to be the same size as all the previous slabs combined, so these allocations become
* exponentially less frequent, just like ByteArrayOutputStream, with one difference. This output stream accepts a
* max capacity hint, which is a hint describing the max amount of data that will be written to this stream. As the
* total size of this stream nears this max, this stream starts to grow linearly instead of exponentially.
* So new slabs are allocated to be 1/5th of the max capacity hint,
* instead of equal to the total previous size of all slabs. This is useful because it prevents allocating roughly
* twice the needed space when a new slab is added just before the stream is done being used.
*
* When reusing this stream it will adjust the initial slab size based on the previous data size, aiming for fewer
* allocations, with the assumption that a similar amount of data will be written to this stream on re-use.
* See ({@link CapacityByteArrayOutputStream#reset()}).
*/
public class CapacityByteArrayOutputStream extends OutputStream {
private static final Logger LOG = LoggerFactory.getLogger(CapacityByteArrayOutputStream.class);
private static final ByteBuffer EMPTY_SLAB = ByteBuffer.wrap(new byte[0]);
private int initialSlabSize;
private final int maxCapacityHint;
private final List slabs = new ArrayList();
private ByteBuffer currentSlab;
private int currentSlabIndex;
private int bytesAllocated = 0;
private int bytesUsed = 0;
private ByteBufferAllocator allocator;
/**
* Return an initial slab size such that a CapacityByteArrayOutputStream constructed with it
* will end up allocating targetNumSlabs in order to reach targetCapacity. This aims to be
* a balance between the overhead of creating new slabs and wasting memory by eagerly making
* initial slabs too big.
*
* Note that targetCapacity here need not match maxCapacityHint in the constructor of
* CapacityByteArrayOutputStream, though often that would make sense.
*
* @param minSlabSize no matter what we shouldn't make slabs any smaller than this
* @param targetCapacity after we've allocated targetNumSlabs how much capacity should we have?
* @param targetNumSlabs how many slabs should it take to reach targetCapacity?
* @return an initial slab size
*/
public static int initialSlabSizeHeuristic(int minSlabSize, int targetCapacity, int targetNumSlabs) {
// initialSlabSize = (targetCapacity / (2^targetNumSlabs)) means we double targetNumSlabs times
// before reaching the targetCapacity
// eg for page size of 1MB we start at 1024 bytes.
// we also don't want to start too small, so we also apply a minimum.
return max(minSlabSize, ((int) (targetCapacity / pow(2, targetNumSlabs))));
}
public static CapacityByteArrayOutputStream withTargetNumSlabs(
int minSlabSize, int maxCapacityHint, int targetNumSlabs) {
return withTargetNumSlabs(minSlabSize, maxCapacityHint, targetNumSlabs, new HeapByteBufferAllocator());
}
/**
* Construct a CapacityByteArrayOutputStream configured such that its initial slab size is
* determined by {@link #initialSlabSizeHeuristic}, with targetCapacity == maxCapacityHint
*
* @param minSlabSize a minimum slab size
* @param maxCapacityHint a hint for the maximum required capacity
* @param targetNumSlabs the target number of slabs
* @param allocator an allocator to use when creating byte buffers for slabs
* @return a capacity baos
*/
public static CapacityByteArrayOutputStream withTargetNumSlabs(
int minSlabSize, int maxCapacityHint, int targetNumSlabs, ByteBufferAllocator allocator) {
return new CapacityByteArrayOutputStream(
initialSlabSizeHeuristic(minSlabSize, maxCapacityHint, targetNumSlabs),
maxCapacityHint, allocator);
}
/**
* Defaults maxCapacityHint to 1MB
* @param initialSlabSize an initial slab size
* @deprecated use {@link CapacityByteArrayOutputStream#CapacityByteArrayOutputStream(int, int, ByteBufferAllocator)}
*/
@Deprecated
public CapacityByteArrayOutputStream(int initialSlabSize) {
this(initialSlabSize, 1024 * 1024, new HeapByteBufferAllocator());
}
/**
* Defaults maxCapacityHint to 1MB
* @param initialSlabSize an initial slab size
* @param allocator an allocator to use when creating byte buffers for slabs
* @deprecated use {@link CapacityByteArrayOutputStream#CapacityByteArrayOutputStream(int, int, ByteBufferAllocator)}
*/
@Deprecated
public CapacityByteArrayOutputStream(int initialSlabSize, ByteBufferAllocator allocator) {
this(initialSlabSize, 1024 * 1024, allocator);
}
/**
* @param initialSlabSize the size to make the first slab
* @param maxCapacityHint a hint (not guarantee) of the max amount of data written to this stream
* @deprecated use {@link CapacityByteArrayOutputStream#CapacityByteArrayOutputStream(int, int, ByteBufferAllocator)}
*/
@Deprecated
public CapacityByteArrayOutputStream(int initialSlabSize, int maxCapacityHint) {
this(initialSlabSize, maxCapacityHint, new HeapByteBufferAllocator());
}
/**
* @param initialSlabSize the size to make the first slab
* @param maxCapacityHint a hint (not guarantee) of the max amount of data written to this stream
* @param allocator an allocator to use when creating byte buffers for slabs
*/
public CapacityByteArrayOutputStream(int initialSlabSize, int maxCapacityHint, ByteBufferAllocator allocator) {
checkArgument(initialSlabSize > 0, "initialSlabSize must be > 0");
checkArgument(maxCapacityHint > 0, "maxCapacityHint must be > 0");
checkArgument(maxCapacityHint >= initialSlabSize, String.format("maxCapacityHint can't be less than initialSlabSize %d %d", initialSlabSize, maxCapacityHint));
this.initialSlabSize = initialSlabSize;
this.maxCapacityHint = maxCapacityHint;
this.allocator = allocator;
reset();
}
/**
* the new slab is guaranteed to be at least minimumSize
* @param minimumSize the size of the data we want to copy in the new slab
*/
private void addSlab(int minimumSize) {
int nextSlabSize;
if (bytesUsed == 0) {
nextSlabSize = initialSlabSize;
} else if (bytesUsed > maxCapacityHint / 5) {
// to avoid an overhead of up to twice the needed size, we get linear when approaching target page size
nextSlabSize = maxCapacityHint / 5;
} else {
// double the size every time
nextSlabSize = bytesUsed;
}
if (nextSlabSize < minimumSize) {
LOG.debug("slab size {} too small for value of size {}. Bumping up slab size", nextSlabSize, minimumSize);
nextSlabSize = minimumSize;
}
LOG.debug("used {} slabs, adding new slab of size {}", slabs.size(), nextSlabSize);
this.currentSlab = allocator.allocate(nextSlabSize);
this.slabs.add(currentSlab);
this.bytesAllocated += nextSlabSize;
this.currentSlabIndex = 0;
}
@Override
public void write(int b) {
if (!currentSlab.hasRemaining()) {
addSlab(1);
}
currentSlab.put(currentSlabIndex, (byte) b);
currentSlabIndex += 1;
currentSlab.position(currentSlabIndex);
bytesUsed += 1;
}
@Override
public void write(byte b[], int off, int len) {
if ((off < 0) || (off > b.length) || (len < 0) ||
((off + len) - b.length > 0)) {
throw new IndexOutOfBoundsException(
String.format("Given byte array of size %d, with requested length(%d) and offset(%d)", b.length, len, off));
}
if (len >= currentSlab.remaining()) {
final int length1 = currentSlab.remaining();
currentSlab.put(b, off, length1);
bytesUsed += length1;
currentSlabIndex += length1;
final int length2 = len - length1;
addSlab(length2);
currentSlab.put(b, off + length1, length2);
currentSlabIndex = length2;
bytesUsed += length2;
} else {
currentSlab.put(b, off, len);
currentSlabIndex += len;
bytesUsed += len;
}
}
private void writeToOutput(OutputStream out, ByteBuffer buf, int len) throws IOException {
if (buf.hasArray()) {
out.write(buf.array(), buf.arrayOffset(), len);
} else {
// The OutputStream interface only takes a byte[], unfortunately this means that a ByteBuffer
// not backed by a byte array must be copied to fulfil this interface
byte[] copy = new byte[len];
buf.flip();
buf.get(copy);
out.write(copy);
}
}
/**
* Writes the complete contents of this buffer to the specified output stream argument. the output
* stream's write method out.write(slab, 0, slab.length)) will be called once per slab.
*
* @param out the output stream to which to write the data.
* @exception IOException if an I/O error occurs.
*/
public void writeTo(OutputStream out) throws IOException {
for (int i = 0; i < slabs.size() - 1; i++) {
writeToOutput(out, slabs.get(i), slabs.get(i).position());
}
writeToOutput(out, currentSlab, currentSlabIndex);
}
/**
* @return The total size in bytes of data written to this stream.
*/
public long size() {
return bytesUsed;
}
/**
*
* @return The total size in bytes currently allocated for this stream.
*/
public int getCapacity() {
return bytesAllocated;
}
/**
* When re-using an instance with reset, it will adjust slab size based on previous data size.
* The intent is to reuse the same instance for the same type of data (for example, the same column).
* The assumption is that the size in the buffer will be consistent.
*/
public void reset() {
// readjust slab size.
// 7 = 2^3 - 1 so that doubling the initial size 3 times will get to the same size
this.initialSlabSize = max(bytesUsed / 7, initialSlabSize);
LOG.debug("initial slab of size {}", initialSlabSize);
for (ByteBuffer slab : slabs) {
allocator.release(slab);
}
this.slabs.clear();
this.bytesAllocated = 0;
this.bytesUsed = 0;
this.currentSlab = EMPTY_SLAB;
this.currentSlabIndex = 0;
}
/**
* @return the index of the last value written to this stream, which
* can be passed to {@link #setByte(long, byte)} in order to change it
*/
public long getCurrentIndex() {
checkArgument(bytesUsed > 0, "This is an empty stream");
return bytesUsed - 1;
}
/**
* Replace the byte stored at position index in this stream with value
*
* @param index which byte to replace
* @param value the value to replace it with
*/
public void setByte(long index, byte value) {
checkArgument(index < bytesUsed, "Index: " + index + " is >= the current size of: " + bytesUsed);
long seen = 0;
for (int i = 0; i < slabs.size(); i++) {
ByteBuffer slab = slabs.get(i);
if (index < seen + slab.limit()) {
// ok found index
slab.put((int)(index-seen), value);
break;
}
seen += slab.limit();
}
}
/**
* @param prefix a prefix to be used for every new line in the string
* @return a text representation of the memory usage of this structure
*/
public String memUsageString(String prefix) {
return format("%s %s %d slabs, %,d bytes", prefix, getClass().getSimpleName(), slabs.size(), getCapacity());
}
/**
* @return the total number of allocated slabs
*/
int getSlabCount() {
return slabs.size();
}
@Override
public void close() {
for (ByteBuffer slab : slabs) {
allocator.release(slab);
}
try {
super.close();
}catch(IOException e){
throw new OutputStreamCloseException(e);
}
}
}
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