rdblue commented on a change in pull request #3966: URL: https://github.com/apache/iceberg/pull/3966#discussion_r803094872
########## File path: core/src/main/java/org/apache/iceberg/util/ZOrderByteUtils.java ########## @@ -0,0 +1,187 @@ +/* + * 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.iceberg.util; + +import java.nio.ByteBuffer; +import java.nio.charset.StandardCharsets; +import java.util.Arrays; + +/** + * Within Z-Ordering the byte representations of objects being compared must be ordered, + * this requires several types to be transformed when converted to bytes. The goal is to + * map object's whose byte representation are not lexicographically ordered into representations + * that are lexicographically ordered. + * Most of these techniques are derived from + * https://aws.amazon.com/blogs/database/z-order-indexing-for-multifaceted-queries-in-amazon-dynamodb-part-2/ + * + * Some implementation is taken from + * https://github.com/apache/hbase/blob/master/hbase-common/src/main/java/org/apache/hadoop/hbase/util/OrderedBytes.java + */ +public class ZOrderByteUtils { + + private ZOrderByteUtils() { + + } + + /** + * Signed ints do not have their bytes in magnitude order because of the sign bit. + * To fix this, flip the sign bit so that all negatives are ordered before positives. This essentially + * shifts the 0 value so that we don't break our ordering when we cross the new 0 value. + */ + public static byte[] intToOrderedBytes(int val, ByteBuffer reuse) { + ByteBuffer bytes = ByteBuffers.reuse(reuse, Integer.BYTES); + bytes.putInt(val ^ 0x80000000); + return bytes.array(); + } + + /** + * Signed longs are treated the same as the signed ints in {@link #intToOrderedBytes(int, ByteBuffer)} + */ + public static byte[] longToOrderedBytes(long val, ByteBuffer reuse) { + ByteBuffer bytes = ByteBuffers.reuse(reuse, Long.BYTES); + bytes.putLong(val ^ 0x8000000000000000L); + return bytes.array(); + } + + /** + * Signed shorts are treated the same as the signed ints in {@link #intToOrderedBytes(int, ByteBuffer)} + */ + public static byte[] shortToOrderedBytes(short val, ByteBuffer reuse) { + ByteBuffer bytes = ByteBuffers.reuse(reuse, Short.BYTES); + bytes.putShort((short) (val ^ (0x8000))); + return bytes.array(); + } + + /** + * Signed tiny ints are treated the same as the signed ints in {@link #intToOrderedBytes(int, ByteBuffer)} + */ + public static byte[] tinyintToOrderedBytes(byte val, ByteBuffer reuse) { + ByteBuffer bytes = ByteBuffers.reuse(reuse, Byte.BYTES); + bytes.put((byte) (val ^ (0x80))); + return bytes.array(); + } + + /** + * IEEE 754 : + * “If two floating-point numbers in the same format are ordered (say, x {@literal <} y), + * they are ordered the same way when their bits are reinterpreted as sign-magnitude integers.” + * + * Which means floats can be treated as sign magnitude integers which can then be converted into lexicographically + * comparable bytes + */ + public static byte[] floatToOrderedBytes(float val, ByteBuffer reuse) { + ByteBuffer bytes = ByteBuffers.reuse(reuse, Float.BYTES); + int ival = Float.floatToIntBits(val); + ival ^= ((ival >> (Integer.SIZE - 1)) | Integer.MIN_VALUE); + bytes.putInt(ival); + return bytes.array(); + } + + /** + * Doubles are treated the same as floats in {@link #floatToOrderedBytes(float, ByteBuffer)} + */ + public static byte[] doubleToOrderedBytes(double val, ByteBuffer reuse) { + ByteBuffer bytes = ByteBuffers.reuse(reuse, Double.BYTES); + long lng = Double.doubleToLongBits(val); + lng ^= ((lng >> (Long.SIZE - 1)) | Long.MIN_VALUE); + bytes.putLong(lng); + return bytes.array(); + } + + /** + * Strings are lexicographically sortable BUT if different byte array lengths will + * ruin the Z-Ordering. (ZOrder requires that a given column contribute the same number of bytes every time). + * This implementation just uses a set size to for all output byte representations. Truncating longer strings + * and right padding 0 for shorter strings. + */ + public static byte[] stringToOrderedBytes(String val, int length, ByteBuffer reuse) { + ByteBuffer bytes = ByteBuffers.reuse(reuse, length); + Arrays.fill(bytes.array(), 0, length, (byte) 0x00); + if (val != null) { + int maxLength = Math.min(length, val.length()); + // We may truncate mid-character + bytes.put(val.getBytes(StandardCharsets.UTF_8), 0, maxLength); + } + return bytes.array(); + } + + /** + * For Testing interleave all available bytes + */ + static byte[] interleaveBits(byte[][] columnsBinary) { + return interleaveBits(columnsBinary, + Arrays.stream(columnsBinary).mapToInt(column -> column.length).sum()); Review comment: @findepi, while those do have different lengths, is it valuable to interleave them directly? We had a discussion above about interleaving short and int. I think that the behavior most people would expect is to interleave by numeric magnitude, not the actual bytes. Basically, if two columns have the same numeric distribution, they should interleave well regardless of the type widths. If you agree there, then what you'd do is cast the integer in your example to a bigint. Then you have 2 8-byte buffers and 1 50-byte buffer. The remainder of the 50 bytes after the first 8 doesn't matter. There are cases where you may want to use different lengths, but to me you should be calling the version with a specified length for those. -- 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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