[GitHub] [hudi] vinothchandar commented on a change in pull request #3952: [HUDI-2102]support hilbert curve for hudi.

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vinothchandar commented on a change in pull request #3952:
URL: https://github.com/apache/hudi/pull/3952#discussion_r754782757



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File path: hudi-client/hudi-client-common/src/main/java/org/apache/hudi/optimize/HilbertCurve.java
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@@ -0,0 +1,321 @@
+/*
+ * 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.hudi.optimize;
+
+import java.math.BigInteger;
+import java.util.Arrays;
+
+/**
+ * Converts between Hilbert index ({@code BigInteger}) and N-dimensional points.
+ *
+ * <p>
+ * Note:
+ * <a href="https://github.com/davidmoten/hilbert-curve/blob/master/src/main/java/org/davidmoten/hilbert/HilbertCurve.java">GitHub</a>).
+ * the Licensed of above link is also http://www.apache.org/licenses/LICENSE-2.0
+ */
+public final class HilbertCurve {
+
+  private final int bits;
+  private final int dimensions;
+  // cached calculations
+  private final int length;
+
+  private HilbertCurve(int bits, int dimensions) {
+    this.bits = bits;
+    this.dimensions = dimensions;
+    // cache a calculated values for small perf improvements
+    this.length = bits * dimensions;
+  }
+
+  /**
+   * Returns a builder for and object that performs transformations for a Hilbert
+   * curve with the given number of bits.
+   *
+   * @param bits
+   *            depth of the Hilbert curve. If bits is one, this is the top-level
+   *            Hilbert curve
+   * @return builder for object to do transformations with the Hilbert Curve
+   */
+  public static Builder bits(int bits) {
+    return new Builder(bits);
+  }
+
+  /**
+   * Builds a {@link HilbertCurve} instance.
+   */
+  public static final class Builder {
+    final int bits;
+
+    private Builder(int bits) {
+      if (bits <= 0  || bits >= 64) {
+        throw new IllegalArgumentException(String.format("bits must be greater than zero and less than 64, now found bits value: %s", bits));
+      }
+      this.bits = bits;
+    }
+
+    public HilbertCurve dimensions(int dimensions) {
+      if (dimensions < 2) {
+        throw new IllegalArgumentException(String.format("dimensions must be at least 2, now found dimensions value: %s", dimensions));
+      }
+      return new HilbertCurve(bits, dimensions);
+    }
+  }
+
+  /**
+   * Converts a point to its Hilbert curve index.
+   *
+   * @param point
+   *            an array of {@code long}. Each ordinate can be between 0 and
+   *            2<sup>bits</sup>-1.
+   * @return index (nonnegative {@link BigInteger})
+   * @throws IllegalArgumentException
+   *             if length of point array is not equal to the number of
+   *             dimensions.
+   */
+  public BigInteger index(long... point) {
+    if (point.length != dimensions) {
+      throw new IllegalArgumentException(String.format("length of point array must equal to the number of dimensions"));
+    }
+    return toIndex(transposedIndex(bits, point));
+  }
+
+  public byte[] indexBytes(long... point) {
+    if (point.length != dimensions) {
+      throw new IllegalArgumentException(String.format("length of point array must equal to the number of dimensions"));
+    }
+    return toIndexBytes(transposedIndex(bits, point));
+  }
+
+  /**
+   * Converts a {@link BigInteger} index (distance along the Hilbert Curve from 0)
+   * to a point of dimensions defined in the constructor of {@code this}.
+   *
+   * @param index
+   *            index along the Hilbert Curve from 0. Maximum value 2 <sup>bits *
+   *            dimensions</sup>-1.
+   * @return array of longs being the point
+   * @throws NullPointerException
+   *             if index is null
+   * @throws IllegalArgumentException
+   *             if index is negative
+   */
+  public long[] point(BigInteger index) {
+    if (index == null) {
+      throw new NullPointerException("index must not be null");
+    }
+    if (index.signum() == -1) {
+      throw new IllegalArgumentException("index cannot be negative");
+    }
+    return transposedIndexToPoint(bits, transpose(index));
+  }
+
+  public void point(BigInteger index, long[] x) {
+    if (index == null) {
+      throw new NullPointerException("index must not be null");
+    }
+    if (index.signum() == -1) {
+      throw new IllegalArgumentException("index cannot be negative");
+    }
+    Arrays.fill(x, 0);
+    transpose(index, x);
+    transposedIndexToPoint(bits, x);
+  }
+
+  public void point(long i, long[] x) {
+    point(BigInteger.valueOf(i), x);
+  }
+
+  /**
+   * Converts a {@code long} index (distance along the Hilbert Curve from 0) to a
+   * point of dimensions defined in the constructor of {@code this}.
+   *
+   * @param index
+   *            index along the Hilbert Curve from 0. Maximum value 2
+   *            <sup>bits+1</sup>-1.
+   * @return array of longs being the point
+   * @throws IllegalArgumentException
+   *             if index is negative
+   */
+  public long[] point(long index) {
+    return point(BigInteger.valueOf(index));
+  }
+
+  /**
+   * Returns the transposed representation of the Hilbert curve index.
+   *
+   * <p>
+   * The Hilbert index is expressed internally as an array of transposed bits.
+   *
+   * <pre>
+   Example: 5 bits for each of n=3 coordinates.
+   15-bit Hilbert integer = A B C D E F G H I J K L M N O is stored
+   as its Transpose                        ^
+   X[0] = A D G J M                    X[2]|  7
+   X[1] = B E H K N        &lt;-------&gt;       | /X[1]

Review comment:
       @alexeykudinkin can you please expand. so @xiarixiaoyao can address/




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