Aklakan commented on code in PR #2405: URL: https://github.com/apache/jena/pull/2405#discussion_r1713422333
########## jena-arq/src/main/java/org/apache/jena/sparql/engine/join/JoinIndex.java: ########## @@ -0,0 +1,175 @@ +/** + * 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.jena.sparql.engine.join; + +import java.util.ArrayList; +import java.util.BitSet; +import java.util.Collections; +import java.util.Iterator; +import java.util.LinkedHashMap; +import java.util.List; +import java.util.Map; +import java.util.Map.Entry; +import java.util.Objects; +import java.util.Set; +import java.util.function.Consumer; + +import org.apache.jena.atlas.iterator.Iter; +import org.apache.jena.sparql.core.Var; +import org.apache.jena.sparql.engine.binding.Binding; +import org.apache.jena.sparql.engine.binding.BindingFactory; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +/** + * A join index contains information about the indexing of a set of rows w.r.t. a join key. + * <p /> + * Consider a primary index for the join key [?x, ?y, ?z]: + * <p /> + * All rows that bind all three variables will be placed into the {@link #mainTable}. + * + * If there is any data that only binds a sub set of the variables, such as [?x, ?z] or [?y], + * then that data will be placed into respective skew tables. + */ +public class JoinIndex + implements Iterable<Binding> +{ + private static final Logger logger = LoggerFactory.getLogger(JoinIndex.class); + + private JoinKey superJoinKey; + + private BitSet mainJoinKeyBitSet; + private HashProbeTable mainTable; + + /** Skew tables hold rows whose variables are a strict sub set of those of this table. */ + private Map<BitSet, HashProbeTable> skewTables; + + public JoinIndex(JoinKey superJoinKey, JoinKey mainJoinKey, BitSet mainJoinKeyBitSet) { + this.superJoinKey = Objects.requireNonNull(superJoinKey); + this.mainJoinKeyBitSet = mainJoinKeyBitSet; + this.mainTable = new HashProbeTable(mainJoinKey); + } + + public BitSet getMainJoinKeyBitSet() { + return mainJoinKeyBitSet; + } + + public HashProbeTable getMainTable() { + return mainTable; + } + + public Set<BitSet> getSkewKeys() { + return skewTables == null ? Collections.emptySet() : skewTables.keySet(); + } + + /** Return a secondary table for the given key. Returns null if there is none. */ + public HashProbeTable getSkewTable(BitSet key) { + return skewTables == null ? null : skewTables.get(key); + } + + public Map<BitSet, HashProbeTable> getSkewTables() { + return skewTables == null ? Collections.emptyMap() : skewTables; + } + + /** Return a secondary table for the given key. Never returns null.*/ + public HashProbeTable getOrCreateSkewTable(BitSet tableKey) { + if (skewTables == null) { + // LinkedHashMap for determinism: Always traverse skew tables in their creation order + skewTables = new LinkedHashMap<>(); + } + HashProbeTable result = skewTables.computeIfAbsent(tableKey, key -> { + List<Var> vars = BitSetMapper.toList(superJoinKey, key); + return new HashProbeTable(JoinKey.create(vars)); + }); + return result; + } + + public void put(Binding row) { + BitSet rawRowKey = BitSetMapper.toBitSet(superJoinKey, row); + + // The next two lines are: effectiveRowKey = bitwiseAnd(primaryKey, rawRowKey) + BitSet effectiveRowKey = (BitSet)mainJoinKeyBitSet.clone(); + effectiveRowKey.and(rawRowKey); + boolean isSameKey = effectiveRowKey.equals(mainJoinKeyBitSet); + + // If there are no joining variables then append the data to the no-key bucket of the main table + if (effectiveRowKey.isEmpty()) { + mainTable.getNoKey$().add(row); + } else if (isSameKey) { + // Hash the row; will never end up in the no-key bucket because that case is handled first + mainTable.put(row); + } else { + HashProbeTable skewTable = getOrCreateSkewTable(effectiveRowKey); + skewTable.put(row); + } + } + + public Iterator<Binding> getCandidates(Binding row) { + if (logger.isTraceEnabled()) { + BitSet joinKeyBitSet = BitSetMapper.toBitSet(superJoinKey, row); + logger.trace("Lookup with " + BitSetMapper.toList(superJoinKey, joinKeyBitSet)); + } + + Iterator<Binding> it = getMainTable().getCandidates(row); // Includes no-key bucket + // it = print(it, "it", logger::trace, logger.isTraceEnabled()); + + if (skewTables != null) { + for (Entry<BitSet, HashProbeTable> entry : skewTables.entrySet()) { + // BitSet skewKey = entry.getKey(); + HashProbeTable skewTable = entry.getValue(); + + Iterator<Binding> subIt = skewTable.getCandidates(row, false); // Excludes no-key bucket which should be empty anyway. + subIt = print(subIt, "subIt", logger::trace, logger.isTraceEnabled()); + + it = Iter.concat(it, subIt); + } + } + it = print(it, "Lookup result for " + row, logger::trace, logger.isTraceEnabled()); Review Comment: Left-over debug statement that needlessly creates a string from each row. -- This is an automated message from the Apache Git Service. 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