gf2121 commented on code in PR #14333: URL: https://github.com/apache/lucene/pull/14333#discussion_r2006876856
########## lucene/core/src/java/org/apache/lucene/codecs/lucene90/blocktree/TrieBuilder.java: ########## @@ -0,0 +1,552 @@ +/* + * 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.codecs.lucene90.blocktree; + +import java.io.IOException; +import java.util.ArrayDeque; +import java.util.Deque; +import java.util.Iterator; +import java.util.LinkedList; +import java.util.List; +import java.util.ListIterator; +import java.util.function.BiConsumer; +import org.apache.lucene.store.DataOutput; +import org.apache.lucene.store.IndexOutput; +import org.apache.lucene.store.RandomAccessInput; +import org.apache.lucene.util.BytesRef; +import org.apache.lucene.util.BytesRefBuilder; + +/** TODO make it a more memory efficient structure */ +class TrieBuilder { + + static final int SIGN_NO_CHILDREN = 0x00; + static final int SIGN_SINGLE_CHILD_WITH_OUTPUT = 0x01; + static final int SIGN_SINGLE_CHILD_WITHOUT_OUTPUT = 0x02; + static final int SIGN_MULTI_CHILDREN = 0x03; + + static final int LEAF_NODE_HAS_TERMS = 1 << 5; + static final int LEAF_NODE_HAS_FLOOR = 1 << 6; + static final long NON_LEAF_NODE_HAS_TERMS = 1L << 1; + static final long NON_LEAF_NODE_HAS_FLOOR = 1L << 0; + + /** + * The output describing the term block the prefix point to. + * + * @param fp describes the on-disk terms block which a trie node points to. + * @param hasTerms A boolean which will be false if this on-disk block consists entirely of + * pointers to child blocks. + * @param floorData A {@link BytesRef} which will be non-null when a large block of terms sharing + * a single trie prefix is split into multiple on-disk blocks. + */ + record Output(long fp, boolean hasTerms, BytesRef floorData) {} + + private enum Status { + BUILDING, + SAVED, + DESTROYED + } + + private static class Node { + + // The utf8 digit that leads to this Node, 0 for root node + private final int label; + // The children listed in order by their utf8 label + private final LinkedList<Node> children; + // The output of this node. + private Output output; + + // Vars used during saving: + + // The file pointer point to where the node saved. -1 means the node has not been saved. + private long fp = -1; + // The iterator whose next() point to the first child has not been saved. + private Iterator<Node> childrenIterator; + + Node(int label, Output output, LinkedList<Node> children) { + this.label = label; + this.output = output; + this.children = children; + } + } + + private Status status = Status.BUILDING; + final Node root = new Node(0, null, new LinkedList<>()); + + static TrieBuilder bytesRefToTrie(BytesRef k, Output v) { + return new TrieBuilder(k, v); + } + + private TrieBuilder(BytesRef k, Output v) { + if (k.length == 0) { + root.output = v; + return; + } + Node parent = root; + for (int i = 0; i < k.length; i++) { + int b = k.bytes[i + k.offset] & 0xFF; + Output output = i == k.length - 1 ? v : null; + Node node = new Node(b, output, new LinkedList<>()); + parent.children.add(node); + parent = node; + } + } + + /** + * Absorb all (K, V) pairs from the given trie into this one. The given trie builder should not + * have key that already exists in this one, otherwise a {@link IllegalArgumentException } will be + * thrown and this trie will get destroyed. + * + * <p>Note: the given trie will be destroyed after absorbing. + */ + void absorb(TrieBuilder trieBuilder) { + if (status != Status.BUILDING || trieBuilder.status != Status.BUILDING) { + throw new IllegalStateException("tries should be unsaved"); + } + // Use a simple stack to avoid recursion. + Deque<Runnable> stack = new ArrayDeque<>(); + stack.add(() -> absorb(this.root, trieBuilder.root, stack)); + while (!stack.isEmpty()) { + stack.pop().run(); + } + trieBuilder.status = Status.DESTROYED; + } + + private void absorb(Node n, Node add, Deque<Runnable> stack) { + assert n.label == add.label; + if (add.output != null) { + if (n.output != null) { + this.status = Status.DESTROYED; + throw new IllegalArgumentException("Duplicated key found in the given trie."); + } + n.output = add.output; + } + ListIterator<Node> iter = n.children.listIterator(); + // TODO we can do more efficient if there is no intersection, block tree always do that + outer: + for (Node addChild : add.children) { + while (iter.hasNext()) { + Node nChild = iter.next(); + if (nChild.label == addChild.label) { + stack.push(() -> absorb(nChild, addChild, stack)); + continue outer; + } + if (nChild.label > addChild.label) { + iter.previous(); // move back + iter.add(addChild); + continue outer; + } + } + iter.add(addChild); + } + } + + Output getEmptyOutput() { + return root.output; + } + + /** Used for tests only. */ + void visit(BiConsumer<BytesRef, Output> consumer) { + assert status == Status.BUILDING; + if (root.output != null) { + consumer.accept(new BytesRef(), root.output); + } + visit(root.children, new BytesRefBuilder(), consumer); + } + + private void visit(List<Node> nodes, BytesRefBuilder key, BiConsumer<BytesRef, Output> consumer) { + for (Node node : nodes) { + key.append((byte) node.label); + if (node.output != null) { + consumer.accept(key.toBytesRef(), node.output); + } + visit(node.children, key, consumer); + key.setLength(key.length() - 1); + } + } + + void save(DataOutput meta, IndexOutput index) throws IOException { + if (status != Status.BUILDING) { + throw new IllegalStateException("only unsaved trie can be saved"); + } + meta.writeVLong(index.getFilePointer()); + saveNodes(index); + meta.writeVLong(root.fp); + index.writeLong(0L); // additional 8 bytes for over-reading + meta.writeVLong(index.getFilePointer()); + status = Status.SAVED; + } + + void saveNodes(IndexOutput index) throws IOException { + final long startFP = index.getFilePointer(); + Deque<Node> stack = new ArrayDeque<>(); + stack.push(root); + + // Visit and save nodes of this trie in a post-order traversal. + + while (stack.isEmpty() == false) { + Node node = stack.peek(); + assert node.fp == -1; + final int childrenNum = node.children.size(); + + if (childrenNum == 0) { + assert node.output != null; + + node.fp = index.getFilePointer() - startFP; + stack.pop(); + + // [n bytes] floor data + // [n bytes] output fp + // [1bit] x | [1bit] has floor | [1bit] has terms | [3bit] output fp bytes | [2bit] sign + + Output output = node.output; + int outputFpBytes = bytesRequiredVLong(output.fp); + int header = + SIGN_NO_CHILDREN + | ((outputFpBytes - 1) << 2) + | (output.hasTerms ? LEAF_NODE_HAS_TERMS : 0) + | (output.floorData != null ? LEAF_NODE_HAS_FLOOR : 0); + index.writeByte(((byte) header)); + writeLongNBytes(output.fp, outputFpBytes, index); + if (output.floorData != null) { + index.writeBytes( + output.floorData.bytes, output.floorData.offset, output.floorData.length); + } + continue; + } + + if (node.childrenIterator == null) { + node.childrenIterator = node.children.iterator(); + } + if (node.childrenIterator.hasNext()) { + stack.push(node.childrenIterator.next()); + continue; + } + + // All children have been written, now it's time to write the parent! + + node.fp = index.getFilePointer() - startFP; + stack.pop(); + + if (childrenNum == 1) { + + // [n bytes] floor data + // [n bytes] encoded output fp | [n bytes] child fp | [1 byte] label + // [3bit] encoded output fp bytes | [3bit] child fp bytes | [2bit] sign + + long childDeltaFp = node.fp - node.children.getFirst().fp; + assert childDeltaFp > 0 : "parent node is always written after children: " + childDeltaFp; + int childFpBytes = bytesRequiredVLong(childDeltaFp); + int encodedOutputFpBytes = + node.output == null ? 0 : bytesRequiredVLong(node.output.fp << 2); + + // TODO if we have only one child and no output, we can store child labels in this node. + // E.g. for a single term trie [foobar], we can save only two nodes [fooba] and [r] + + int sign = + node.output != null ? SIGN_SINGLE_CHILD_WITH_OUTPUT : SIGN_SINGLE_CHILD_WITHOUT_OUTPUT; + int header = sign | ((childFpBytes - 1) << 2) | ((encodedOutputFpBytes - 1) << 5); + index.writeByte((byte) header); + index.writeByte((byte) node.children.getFirst().label); + writeLongNBytes(childDeltaFp, childFpBytes, index); + + if (node.output != null) { + Output output = node.output; + long encodedFp = encodeFP(output); + writeLongNBytes(encodedFp, encodedOutputFpBytes, index); + if (output.floorData != null) { + index.writeBytes( + output.floorData.bytes, output.floorData.offset, output.floorData.length); + } + } + } else { + + // [n bytes] floor data + // [n bytes] children fps | [n bytes] position data + // [1 byte] children count (if floor data) | [n bytes] encoded output fp | [1 byte] label + // [5bit] position bytes | 2bit children strategy | [3bit] encoded output fp bytes + // [1bit] has output | [3bit] children fp bytes | [2bit] sign + + final int minLabel = node.children.getFirst().label; + final int maxLabel = node.children.getLast().label; + PositionStrategy positionStrategy = null; + int positionBytes = Integer.MAX_VALUE; + for (PositionStrategy strategy : PositionStrategy.values()) { + int strategyCost = strategy.positionBytes(minLabel, maxLabel, childrenNum); + if (strategyCost < positionBytes) { + positionStrategy = strategy; + positionBytes = strategyCost; + } else if (positionStrategy != null + && strategyCost == positionBytes + && strategy.priority > positionStrategy.priority) { + positionStrategy = strategy; + } + } + + assert positionStrategy != null; + assert positionBytes > 0 && positionBytes <= 32; + + long maxChildDeltaFp = node.fp - node.children.getFirst().fp; + assert maxChildDeltaFp > 0; + int childrenFpBytes = bytesRequiredVLong(maxChildDeltaFp); + int encodedOutputFpBytes = + node.output == null ? 1 : bytesRequiredVLong(node.output.fp << 2); + int header = + SIGN_MULTI_CHILDREN + | ((childrenFpBytes - 1) << 2) + | ((node.output != null ? 1 : 0) << 5) + | ((encodedOutputFpBytes - 1) << 6) + | (positionStrategy.priority << 9) + | ((positionBytes - 1) << 11) + | (minLabel << 16); + + writeLongNBytes(header, 3, index); + + if (node.output != null) { + Output output = node.output; + long encodedFp = encodeFP(output); + writeLongNBytes(encodedFp, encodedOutputFpBytes, index); + if (output.floorData != null) { + index.writeByte((byte) (childrenNum - 1)); + } + } + + long positionStartFp = index.getFilePointer(); + positionStrategy.save(node.children, childrenNum, positionBytes, index); + assert index.getFilePointer() == positionStartFp + positionBytes + : positionStrategy.name() + + " position bytes compute error, computed: " + + positionBytes + + " actual: " + + (index.getFilePointer() - positionStartFp); + + for (Node child : node.children) { + assert node.fp > child.fp; + writeLongNBytes(node.fp - child.fp, childrenFpBytes, index); + } + + if (node.output != null && node.output.floorData != null) { + BytesRef floorData = node.output.floorData; + index.writeBytes(floorData.bytes, floorData.offset, floorData.length); + } + } + } + } + + private long encodeFP(Output output) { + assert output.fp < 1L << 62; + return (output.floorData != null ? NON_LEAF_NODE_HAS_FLOOR : 0) + | (output.hasTerms ? NON_LEAF_NODE_HAS_TERMS : 0) + | (output.fp << 2); + } + + private static int bytesRequiredVLong(long v) { + return Long.BYTES - (Long.numberOfLeadingZeros(v | 1) >>> 3); + } + + private static void writeLongNBytes(long v, int n, DataOutput out) throws IOException { + for (int i = 0; i < n; i++) { + out.writeByte((byte) v); + v >>= 8; + } + } + + enum PositionStrategy { + + /** + * Store children labels in a bitset, this is likely the most efficient storage as we can + * compute position with bitCount instruction, so we give it the highest priority. + */ + BITS(2) { + @Override + int positionBytes(int minLabel, int maxLabel, int labelCnt) { + int byteDistance = maxLabel - minLabel + 1; + return (byteDistance + 7) >>> 3; + } + + @Override + void save(List<Node> children, int labelCnt, int positionBytes, IndexOutput output) + throws IOException { + byte presenceBits = 1; // The first arc is always present. + int presenceIndex = 0; + int previousLabel = children.getFirst().label; + for (int arcIdx = 1; arcIdx < children.size(); arcIdx++) { + int label = children.get(arcIdx).label; + assert label > previousLabel; + presenceIndex += label - previousLabel; + while (presenceIndex >= Byte.SIZE) { + output.writeByte(presenceBits); + presenceBits = 0; + presenceIndex -= Byte.SIZE; + } + // Set the bit at presenceIndex to flag that the corresponding arc is present. + presenceBits |= 1 << presenceIndex; + previousLabel = label; + } + assert presenceIndex == (children.getLast().label - children.getFirst().label) % 8; + assert presenceBits != 0; // The last byte is not 0. + assert (presenceBits & (1 << presenceIndex)) != 0; // The last arc is always present. + output.writeByte(presenceBits); + } + + @Override + int lookup( + int targetLabel, RandomAccessInput in, long offset, int positionBytes, int minLabel) + throws IOException { + int bitIndex = targetLabel - minLabel; + if (bitIndex >= (positionBytes << 3)) { + return -1; + } + int wordIndex = bitIndex >>> 6; + long wordFp = offset + (wordIndex << 3); + long word = in.readLong(wordFp); + long mask = 1L << bitIndex; + if ((word & mask) == 0) { + return -1; + } + int pos = 0; + for (long fp = offset; fp < wordFp; fp += 8L) { + pos += Long.bitCount(in.readLong(fp)); + } + pos += Long.bitCount(word & (mask - 1)); + return pos; + } + }, + + /** + * Store labels in an array and lookup with binary search. + * + * <p>TODO: Can we use VectorAPI to speed up the lookup? we can check 64 labels once on AVX512! + */ + ARRAY(1) { + @Override + int positionBytes(int minLabel, int maxLabel, int labelCnt) { + return labelCnt - 1; // min label saved + } + + @Override + void save(List<Node> children, int labelCnt, int positionBytes, IndexOutput output) + throws IOException { + for (int i = 1; i < labelCnt; i++) { + output.writeByte((byte) children.get(i).label); + } + } + + @Override + int lookup( + int targetLabel, RandomAccessInput in, long offset, int positionBytes, int minLabel) + throws IOException { + int low = 0; + int high = positionBytes - 1; + while (low <= high) { + int mid = (low + high) >>> 1; + int midLabel = in.readByte(offset + mid) & 0xFF; + if (midLabel < targetLabel) { + low = mid + 1; + } else if (midLabel > targetLabel) { + high = mid - 1; + } else { + return mid + 1; // min label not included, plus 1 + } + } + return -1; + } + }, + + /** + * Store labels that not existing within the range. E.g. store 10(max label) and 3, 5(absent + * label) for [1, 2, 4, 6, 7, 8, 9, 10] + * + * <p>TODO: Can we use VectorAPI to speed up the lookup? we can check 64 labels once on AVX512! + */ + REVERSE_ARRAY(0) { + + @Override + int positionBytes(int minLabel, int maxLabel, int labelCnt) { + int byteDistance = maxLabel - minLabel + 1; + return byteDistance - labelCnt + 1; + } + + @Override + void save(List<Node> children, int labelCnt, int positionBytes, IndexOutput output) + throws IOException { + output.writeByte((byte) children.getLast().label); + int lastLabel = children.getFirst().label; + for (int i = 1; i < labelCnt; i++) { + Node node = children.get(i); + while (++lastLabel < node.label) { + output.writeByte((byte) lastLabel); + } + } + } + + @Override + int lookup( + int targetLabel, RandomAccessInput in, long offset, int positionBytes, int minLabel) + throws IOException { + int maxLabel = in.readByte(offset++) & 0xFF; + if (targetLabel >= maxLabel) { + return targetLabel == maxLabel ? maxLabel - minLabel - positionBytes + 1 : -1; + } + if (positionBytes == 1) { + return targetLabel - minLabel; + } + + int low = 0; + int high = positionBytes - 2; + while (low <= high) { + int mid = (low + high) >>> 1; + int midLabel = in.readByte(offset + mid) & 0xFF; + if (midLabel < targetLabel) { + low = mid + 1; + } else if (midLabel > targetLabel) { + high = mid - 1; + } else { + return -1; + } + } + return targetLabel - minLabel - low; + } + }; + + private static final PositionStrategy[] STRATEGIES = new PositionStrategy[3]; + + static { + for (PositionStrategy strategy : PositionStrategy.values()) { + STRATEGIES[strategy.priority] = strategy; + } + } + + final int priority; + + PositionStrategy(int priority) { + this.priority = priority; + } + + abstract int positionBytes(int minLabel, int maxLabel, int labelCnt); + + abstract void save(List<Node> children, int labelCnt, int positionBytes, IndexOutput output) + throws IOException; + + abstract int lookup( + int targetLabel, RandomAccessInput in, long offset, int positionBytes, int minLabel) + throws IOException; + + static PositionStrategy byCode(int code) { Review Comment: Good point. I'm considering make `priority` only a `code`, declare strategy enums in priority order, and have a test for this. In this way, code is just to identify which strategy is used, and we can easily define a new strategy in any priority. -- 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. To unsubscribe, e-mail: issues-unsubscr...@lucene.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@lucene.apache.org For additional commands, e-mail: issues-h...@lucene.apache.org
