rdblue commented on a change in pull request #3966: URL: https://github.com/apache/iceberg/pull/3966#discussion_r801084085
########## File path: core/src/test/java/org/apache/iceberg/util/TestZOrderByteUtil.java ########## @@ -0,0 +1,260 @@ +/* + * 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.util.Arrays; +import java.util.Random; +import org.apache.iceberg.relocated.com.google.common.primitives.UnsignedBytes; +import org.apache.iceberg.types.Types; +import org.junit.Assert; +import org.junit.Test; + +public class TestZOrderByteUtil { + private static final byte IIIIIIII = (byte) 255; + private static final byte IOIOIOIO = (byte) 170; + private static final byte OIOIOIOI = (byte) 85; + private static final byte OOOOIIII = (byte) 15; + private static final byte OOOOOOOI = (byte) 1; + private static final byte OOOOOOOO = (byte) 0; + + private static final int NUM_TESTS = 100000; + + private final Random random = new Random(42); + + private String bytesToString(byte[] bytes) { + StringBuilder result = new StringBuilder(); + for (byte b : bytes) { + result.append(String.format("%8s", Integer.toBinaryString(b & 0xFF)).replace(' ', '0')); + } + return result.toString(); + } + + /** + * Returns a non-0 length byte array + */ + private byte[] generateRandomBytes() { + int length = Math.abs(random.nextInt(100) + 1); + byte[] result = new byte[length]; + random.nextBytes(result); + return result; + } + + /** + * Test method to ensure correctness of byte interleaving code + */ + private String interleaveStrings(String[] strings) { + StringBuilder result = new StringBuilder(); + int totalLength = Arrays.stream(strings).mapToInt(String::length).sum(); + int substringIndex = 0; + int characterIndex = 0; + while (characterIndex < totalLength) { + for (String str : strings) { + if (substringIndex < str.length()) { + result.append(str.charAt(substringIndex)); + characterIndex++; + } + } + substringIndex++; + } + return result.toString(); + } + + /** + * Compares the result of a string based interleaving algorithm implemented above + * versus the binary bit-shifting algorithm used in ZOrderByteUtils. Either both + * algorithms are identically wrong or are both identically correct. + */ + @Test + public void testInterleaveRandomExamples() { + for (int test = 0; test < NUM_TESTS; test++) { + int numByteArrays = Math.abs(random.nextInt(6)) + 1; + byte[][] testBytes = new byte[numByteArrays][]; + String[] testStrings = new String[numByteArrays]; + for (int byteIndex = 0; byteIndex < numByteArrays; byteIndex++) { + testBytes[byteIndex] = generateRandomBytes(); + testStrings[byteIndex] = bytesToString(testBytes[byteIndex]); + } + byte[] byteResult = ZOrderByteUtils.interleaveBits(testBytes); + String byteResultAsString = bytesToString(byteResult); + + String stringResult = interleaveStrings(testStrings); + + Assert.assertEquals("String interleave didn't match byte interleave", stringResult, byteResultAsString); + } + } + + @Test + public void testInterleaveEmptyBits() { + byte[][] test = new byte[4][10]; + byte[] expected = new byte[40]; + + Assert.assertArrayEquals("Should combine empty arrays", + expected, ZOrderByteUtils.interleaveBits(test)); + } + + @Test + public void testInterleaveFullBits() { + byte[][] test = new byte[4][]; + test[0] = new byte[]{IIIIIIII, IIIIIIII}; + test[1] = new byte[]{IIIIIIII}; + test[2] = new byte[0]; + test[3] = new byte[]{IIIIIIII, IIIIIIII, IIIIIIII}; + byte[] expected = new byte[]{IIIIIIII, IIIIIIII, IIIIIIII, IIIIIIII, IIIIIIII, IIIIIIII}; + + Assert.assertArrayEquals("Should combine full arrays", + expected, ZOrderByteUtils.interleaveBits(test)); + } + + @Test + public void testInterleaveMixedBits() { Review comment: There's another simple option that I think solves an additional challenge... I'd propose that we cast everything to float so we don't have to worry about choosing a type and converting everything to it. That also gives us a more compact representation that is better for packing multiple columns. That's because floating point values are represented as scientific notation with base-2. The exponent encodes how many positions the fraction was shifted so that its first digit is a 1. Alternatively, you can think of it as encoding how many bits at the start of the number are 0, then storing a normalized fraction. That effectively compresses the most significant parts of a number into the highest bits. For float32, there's a sign bit, 8 bits of exponent, and 23 bits of fraction (mantissa). Converting all the values to floating point would solve the immediate problem because all numbers would use the same representation, giving what I think is the expected behavior. But it also means that we can fit more columns in 32 bits or 64 bits, which are going to be much faster for comparison once we pass them off to Spark. For example, if we took 4 integers and interleaved them, it would take 128 bits. But if we convert those to float first, then the most significant parts can fit in half that: 16 bits per value can carry the sign bit, the full 8-bit exponent, and 7 bits of the fraction. That's about 128 partitions of the number space per exponent value. If you don't want to lose so much of the value, then fewer columns do better. And we can always fall back to producing the full byte array if we want. What do you guys think? -- 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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