liyafan82 commented on a change in pull request #9769: URL: https://github.com/apache/arrow/pull/9769#discussion_r601038372
########## 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 have revised the JavaDoc to clarify the buffer ownership. Thanks. The method of passing in only the compressed data sounds good to me. However, there are some problem when implementing the `doDecompress` method: it may also need the uncompressed size (e.g. to allocate some internal data structures, like on-heap array in our implementation). Such information can be obtained from the size of the passed-in buffer. However, the buffer size can be larger than the uncompressed size, which may cause waste of memory. We can also change the interface to pass in the uncompressed size, but this would make the interface more complicated and asymmetric. So I have keeped the interface unchanged. If you feel strong about it, we can change the interface in that way. -- 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. 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