jpountz commented on code in PR #15140: URL: https://github.com/apache/lucene/pull/15140#discussion_r2315157676
########## lucene/CHANGES.txt: ########## @@ -130,6 +130,8 @@ API Changes instance instead of a Bits instance to identify document IDs to filter. (Shubham Chaudhary, Adrien Grand) +* GITHUB#15140: Optimize TopScoreDocCollector with TernaryLongHeap for improved performance over Binary-LongHeap. (Ramakrishna Chilaka) Review Comment: Can you move it to the 10.4 section now that the 10.4 branch has been cut? ########## lucene/core/src/java/org/apache/lucene/util/TernaryLongHeap.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.lucene.util; + +import java.util.Arrays; + +/** + * A ternary min heap that stores longs; a primitive priority queue that like all priority queues + * maintains a partial ordering of its elements such that the least element can always be found in + * constant time. Put()'s and pop()'s require log_3(size). This heap provides unbounded growth via + * {@link #push(long)}, and bounded-size insertion based on its nominal maxSize via {@link + * #insertWithOverflow(long)}. The heap is a min heap, meaning that the top element is the lowest + * value of the heap. TernaryLongHeap implements 3-ary heap. + * + * @lucene.internal + */ +public final class TernaryLongHeap { + + private final int maxSize; + + private long[] heap; + private int size = 0; + + /** + * Constructs a heap with specified size and initializes all elements with the given value. + * + * @param size the number of elements to initialize in the heap. + * @param initialValue the value to fill the heap with. + */ + public TernaryLongHeap(int size, long initialValue) { + this(size <= 0 ? 1 : size); + Arrays.fill(heap, 1, size + 1, initialValue); + this.size = size; + } + + /** + * Create an empty priority queue of the configured initial size. + * + * @param maxSize the maximum size of the heap, or if negative, the initial size of an unbounded + * heap + */ + public TernaryLongHeap(int maxSize) { + if (maxSize < 1 || maxSize >= ArrayUtil.MAX_ARRAY_LENGTH) { + // Throw exception to prevent confusing OOME: + throw new IllegalArgumentException( + "maxSize must be > 0 and < " + (ArrayUtil.MAX_ARRAY_LENGTH - 1) + "; got: " + maxSize); + } + // NOTE: we add +1 because all access to heap is 1-based not 0-based. heap[0] is unused. + final int heapSize = maxSize + 1; + this.maxSize = maxSize; + this.heap = new long[heapSize]; + } + + /** + * Adds a value in log(size) time. Grows unbounded as needed to accommodate new values. + * + * @return the new 'top' element in the queue. + */ + public long push(long element) { + size++; + if (size == heap.length) { + heap = ArrayUtil.grow(heap, (size * 3 + 1) / 2); + } + heap[size] = element; + LongHeap.upHeap(heap, size, 3); + return heap[1]; + } + + /** + * Adds a value to an TernaryLongHeap in log(size) time. If the number of values would exceed the + * heap's maxSize, the least value is discarded. + * + * @return whether the value was added (unless the heap is full, or the new value is less than the + * top value) + */ + public boolean insertWithOverflow(long value) { + if (size >= maxSize) { + if (value < heap[1]) { + return false; + } + updateTop(value); + return true; + } + push(value); + return true; + } + + /** + * Returns the least element of the TernaryLongHeap in constant time. It is up to the caller to + * verify that the heap is not empty; no checking is done, and if no elements have been added, 0 + * is returned. + */ + public long top() { + return heap[1]; + } + + /** + * Removes and returns the least element of the PriorityQueue in log(size) time. + * + * @throws IllegalStateException if the TernaryLongHeap is empty. + */ + public long pop() { + if (size > 0) { + long result = heap[1]; // save first value + heap[1] = heap[size]; // move last to first + size--; + LongHeap.downHeap(heap, 1, size, 3); // adjust heap Review Comment: nit: let's have a `ARITY = 3` constant instead of inlining 3? ########## lucene/core/src/java/org/apache/lucene/util/LongHeap.java: ########## @@ -216,4 +216,63 @@ public long get(int i) { long[] getHeapArray() { return heap; } + + /** + * Restores heap order by moving an element up the heap until it finds its proper position. Works + * with heaps of any arity (number of children per node). + * + * @param heap the heap array (1-based indexing) + * @param i the index of the element to move up + * @param arity the number of children each node can have + */ + static void upHeap(long[] heap, int i, int arity) { + final long value = heap[i]; // save bottom value + while (i > 1) { + // parent formula for 1-based indexing + final int parent = ((i - 2) / arity) + 1; + final long parentVal = heap[parent]; + if (value >= parentVal) break; + heap[i] = parentVal; // shift parent down + i = parent; + } + heap[i] = value; // install saved value + } + + /** + * Restores heap order by moving an element down the heap until it finds its proper position. + * Works with heaps of any arity (number of children per node). + * + * @param heap the heap array (1-based indexing) + * @param i the index of the element to move down + * @param size the current size of the heap + * @param arity the number of children each node can have + */ + static void downHeap(long[] heap, int i, int size, int arity) { + long value = heap[i]; // save top value + for (; ; ) { + // first child formula for 1-based indexing + int firstChild = arity * (i - 1) + 2; + if (firstChild > size) break; // i is a leaf + + int lastChild = Math.min(firstChild + arity - 1, size); + + // find the smallest child in [firstChild, lastChild] + int best = firstChild; + long bestVal = heap[firstChild]; + + for (int c = firstChild + 1; c <= lastChild; c++) { + final long v = heap[c]; + if (v < bestVal) { + bestVal = v; + best = c; + } + } + + if (bestVal >= value) break; + + heap[i] = bestVal; + i = best; + } + heap[i] = value; // install saved value + } Review Comment: Let's move these helpers to `TernaryLongHeap` since they're not used here and only used there? ########## lucene/core/src/java/org/apache/lucene/util/TernaryLongHeap.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.lucene.util; + +import java.util.Arrays; + +/** + * A ternary min heap that stores longs; a primitive priority queue that like all priority queues + * maintains a partial ordering of its elements such that the least element can always be found in + * constant time. Put()'s and pop()'s require log_3(size). This heap provides unbounded growth via + * {@link #push(long)}, and bounded-size insertion based on its nominal maxSize via {@link + * #insertWithOverflow(long)}. The heap is a min heap, meaning that the top element is the lowest + * value of the heap. TernaryLongHeap implements 3-ary heap. + * + * @lucene.internal + */ +public final class TernaryLongHeap { + + private final int maxSize; + + private long[] heap; + private int size = 0; + + /** + * Constructs a heap with specified size and initializes all elements with the given value. + * + * @param size the number of elements to initialize in the heap. + * @param initialValue the value to fill the heap with. + */ + public TernaryLongHeap(int size, long initialValue) { + this(size <= 0 ? 1 : size); + Arrays.fill(heap, 1, size + 1, initialValue); + this.size = size; + } + + /** + * Create an empty priority queue of the configured initial size. + * + * @param maxSize the maximum size of the heap, or if negative, the initial size of an unbounded + * heap + */ + public TernaryLongHeap(int maxSize) { + if (maxSize < 1 || maxSize >= ArrayUtil.MAX_ARRAY_LENGTH) { + // Throw exception to prevent confusing OOME: + throw new IllegalArgumentException( + "maxSize must be > 0 and < " + (ArrayUtil.MAX_ARRAY_LENGTH - 1) + "; got: " + maxSize); + } + // NOTE: we add +1 because all access to heap is 1-based not 0-based. heap[0] is unused. + final int heapSize = maxSize + 1; + this.maxSize = maxSize; + this.heap = new long[heapSize]; + } + + /** + * Adds a value in log(size) time. Grows unbounded as needed to accommodate new values. + * + * @return the new 'top' element in the queue. + */ + public long push(long element) { + size++; + if (size == heap.length) { + heap = ArrayUtil.grow(heap, (size * 3 + 1) / 2); + } + heap[size] = element; + LongHeap.upHeap(heap, size, 3); + return heap[1]; + } Review Comment: I had not realized that LongHeap grows unbounded on-demand. This doesn't feel right when the ctor takes a `maxSize` parameter. Not related to your PR but we should fix it in a separate PR? -- 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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