org.apache.parquet.column.values.deltastrings.DeltaByteArrayReader 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.parquet.column.values.deltastrings;
import java.io.IOException;
import org.apache.parquet.bytes.ByteBufferInputStream;
import org.apache.parquet.column.values.RequiresPreviousReader;
import org.apache.parquet.column.values.ValuesReader;
import org.apache.parquet.column.values.delta.DeltaBinaryPackingValuesReader;
import org.apache.parquet.column.values.deltalengthbytearray.DeltaLengthByteArrayValuesReader;
import org.apache.parquet.io.api.Binary;
/**
* Reads binary data written by {@link DeltaByteArrayWriter}
*/
public class DeltaByteArrayReader extends ValuesReader implements RequiresPreviousReader {
private ValuesReader prefixLengthReader;
private ValuesReader suffixReader;
private Binary previous;
public DeltaByteArrayReader() {
this.prefixLengthReader = new DeltaBinaryPackingValuesReader();
this.suffixReader = new DeltaLengthByteArrayValuesReader();
this.previous = Binary.fromConstantByteArray(new byte[0]);
}
@Override
public void initFromPage(int valueCount, ByteBufferInputStream stream)
throws IOException {
prefixLengthReader.initFromPage(valueCount, stream);
suffixReader.initFromPage(valueCount, stream);
}
@Override
public void skip() {
// read the next value to skip so that previous is correct.
readBytes();
}
@Override
public Binary readBytes() {
int prefixLength = prefixLengthReader.readInteger();
// This does not copy bytes
Binary suffix = suffixReader.readBytes();
int length = prefixLength + suffix.length();
// NOTE: due to PARQUET-246, it is important that we
// respect prefixLength which was read from prefixLengthReader,
// even for the *first* value of a page. Even though the first
// value of the page should have an empty prefix, it may not
// because of PARQUET-246.
// We have to do this to materialize the output
if(prefixLength != 0) {
byte[] out = new byte[length];
System.arraycopy(previous.getBytesUnsafe(), 0, out, 0, prefixLength);
System.arraycopy(suffix.getBytesUnsafe(), 0, out, prefixLength, suffix.length());
previous = Binary.fromConstantByteArray(out);
} else {
previous = suffix;
}
return previous;
}
/**
* There was a bug (PARQUET-246) in which DeltaByteArrayWriter's reset() method did not
* clear the previous value state that it tracks internally. This resulted in the first
* value of all pages (except for the first page) to be a delta from the last value of the
* previous page. In order to read corrupted files written with this bug, when reading a
* new page we need to recover the previous page's last value to use it (if needed) to
* read the first value.
*/
@Override
public void setPreviousReader(ValuesReader reader) {
if (reader != null) {
this.previous = ((DeltaByteArrayReader) reader).previous;
}
}
}