emkornfield commented on a change in pull request #9769: URL: https://github.com/apache/arrow/pull/9769#discussion_r601110118
########## File path: java/vector/src/main/java/org/apache/arrow/vector/compression/AbstractCompressionCodec.java ########## @@ -0,0 +1,117 @@ +/* + * 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.arrow.vector.compression; + +import org.apache.arrow.memory.ArrowBuf; +import org.apache.arrow.memory.BufferAllocator; +import org.apache.arrow.memory.util.MemoryUtil; +import org.apache.arrow.util.Preconditions; + +/** + * The base class for concrete compression codecs, providing + * common logic for all compression codecs. + */ +public abstract class AbstractCompressionCodec implements CompressionCodec { + + @Override + public ArrowBuf compress(BufferAllocator allocator, ArrowBuf uncompressedBuffer) { + Preconditions.checkArgument(uncompressedBuffer.writerIndex() <= Integer.MAX_VALUE, + "The uncompressed buffer size exceeds the integer limit"); + + if (uncompressedBuffer.writerIndex() == 0L) { + // shortcut for empty buffer + ArrowBuf compressedBuffer = allocator.buffer(CompressionUtil.SIZE_OF_UNCOMPRESSED_LENGTH); + compressedBuffer.setLong(0, 0); + compressedBuffer.writerIndex(CompressionUtil.SIZE_OF_UNCOMPRESSED_LENGTH); + uncompressedBuffer.close(); + return compressedBuffer; + } + + ArrowBuf compressedBuffer = doCompress(allocator, uncompressedBuffer); + long compressedLength = compressedBuffer.writerIndex() - CompressionUtil.SIZE_OF_UNCOMPRESSED_LENGTH; + long uncompressedLength = uncompressedBuffer.writerIndex(); + + if (compressedLength > uncompressedLength) { + // compressed buffer is larger, send the raw buffer + compressedBuffer.close(); + compressedBuffer = CompressionUtil.packageRawBuffer(allocator, uncompressedBuffer); + } else { + writeUncompressedLength(compressedBuffer, uncompressedLength); + } + + uncompressedBuffer.close(); + return compressedBuffer; + } + + @Override + public ArrowBuf decompress(BufferAllocator allocator, ArrowBuf compressedBuffer) { + Preconditions.checkArgument(compressedBuffer.writerIndex() <= Integer.MAX_VALUE, + "The compressed buffer size exceeds the integer limit"); + + Preconditions.checkArgument(compressedBuffer.writerIndex() >= CompressionUtil.SIZE_OF_UNCOMPRESSED_LENGTH, + "Not enough data to decompress."); + + long decompressedLength = compressedBuffer.getLong(0); + if (!MemoryUtil.LITTLE_ENDIAN) { + decompressedLength = Long.reverseBytes(decompressedLength); + } + + if (decompressedLength == 0L) { + // shortcut for empty buffer + compressedBuffer.close(); + return allocator.getEmpty(); + } + + if (decompressedLength == CompressionUtil.NO_COMPRESSION_LENGTH) { + // no compression + return CompressionUtil.extractUncompressedBuffer(compressedBuffer); + } + + ArrowBuf decompressedBuffer = doDecompress(allocator, compressedBuffer); + compressedBuffer.close(); + return decompressedBuffer; + } + + protected void writeUncompressedLength(ArrowBuf compressedBuffer, long uncompressedLength) { + if (!MemoryUtil.LITTLE_ENDIAN) { + uncompressedLength = Long.reverseBytes(uncompressedLength); + } + // first 8 bytes reserved for uncompressed length, according to the specification + compressedBuffer.setLong(0, uncompressedLength); + } + + protected long readUncompressedLength(ArrowBuf compressedBuffer) { + long decompressedLength = compressedBuffer.getLong(0); + if (!MemoryUtil.LITTLE_ENDIAN) { + decompressedLength = Long.reverseBytes(decompressedLength); + } + return decompressedLength; + } + + /** + * The method that actually performs the data compression. + * Please note that the first 8 bytes of the compressed buffer is reserved for the uncompressed size. + */ + protected abstract ArrowBuf doCompress(BufferAllocator allocator, ArrowBuf uncompressedBuffer); + + /** + * The method that actually performs the data decompression. + * Please note that the first 8 bytes of the compressed buffer is reserved for the uncompressed size. Review comment: I would like to try to avoid using writerIndex if possible. What I was thinking originally, is that a new ArrowBuf with capacity equal to the decompressed size is passed in. So implementations can simply reference buffer size to know uncompressed size, and can allocate additional buffers if needed for scratch. writerIndex would be zero (and ideally would not be touched by the implementations). At least looking at the zstd and lz4 c apis, it looks like both support this type of contract (extra output buffer padding doesn't seem necessary). -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org
