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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.search.predicate.index;
import com.google.common.collect.MinMaxPriorityQueue;
import org.eclipse.collections.api.tuple.primitive.ObjectLongPair;
import org.eclipse.collections.impl.map.mutable.primitive.ObjectIntHashMap;
import org.eclipse.collections.impl.map.mutable.primitive.ObjectLongHashMap;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
/**
* Counts the number of posting lists per document id.
* Caches the most expensive posting list in a bit vector.
*
* @author bjorncs
*/
public class CachedPostingListCounter {
// Only use bit vector for counting if the documents covered is more than the threshold (relative to nDocuments)
private static final double THRESHOLD_USE_BIT_VECTOR = 1;
private final int nDocuments;
private final ObjectLongHashMap<int[]> frequency = new ObjectLongHashMap<>();
private final ObjectIntHashMap<int[]> postingListMapping;
private final int[] bitVector;
public CachedPostingListCounter(int nDocuments) {
this.nDocuments = nDocuments;
this.postingListMapping = new ObjectIntHashMap<>();
this.bitVector = new int[0];
}
private CachedPostingListCounter(ObjectIntHashMap<int[]> postingListMapping, int[] bitVector) {
this.nDocuments = bitVector.length;
this.postingListMapping = postingListMapping;
this.bitVector = bitVector;
}
public synchronized void registerUsage(List<PostingList> postingLists) {
for (PostingList postingList : postingLists) {
frequency.updateValue(postingList.getDocIds(), 0, v -> v + 1);
}
}
public void countPostingListsPerDocument(List<PostingList> postingLists, byte[] nPostingListsForDocument) {
Arrays.fill(nPostingListsForDocument, (byte) 0);
List<int[]> nonCachedPostingLists = new ArrayList<>(postingLists.size());
List<int[]> cachedPostingLists = new ArrayList<>(postingLists.size());
long nDocumentsCachedPostingLists = 0;
int postingListBitmap = 0;
for (PostingList postingList : postingLists) {
int[] docIds = postingList.getDocIds();
int index = postingListMapping.getIfAbsent(docIds, -1);
if (index >= 0) {
cachedPostingLists.add(docIds);
postingListBitmap |= (1 << index);
nDocumentsCachedPostingLists += docIds.length;
} else {
nonCachedPostingLists.add(docIds);
}
}
if (postingListBitmap != 0) {
if (nDocumentsCachedPostingLists > nDocuments * THRESHOLD_USE_BIT_VECTOR) {
countUsingBitVector(nPostingListsForDocument, postingListBitmap);
} else {
nonCachedPostingLists.addAll(cachedPostingLists);
}
}
if (!nonCachedPostingLists.isEmpty()) {
countUsingDocIdIteration(nPostingListsForDocument, nonCachedPostingLists);
}
}
private void countUsingBitVector(byte[] nPostingListsForDocument, int postingListBitmap) {
for (int docId = 0; docId < nDocuments; docId++) {
nPostingListsForDocument[docId] += (byte)Integer.bitCount(bitVector[docId] & postingListBitmap);
}
}
private static void countUsingDocIdIteration(byte[] nPostingListsForDocument, List<int[]> nonCachedPostingLists) {
for (int[] docIds : nonCachedPostingLists) {
for (int docId : docIds) {
++nPostingListsForDocument[docId];
}
}
}
public CachedPostingListCounter rebuildCache() {
MinMaxPriorityQueue<Entry> mostExpensive = MinMaxPriorityQueue.maximumSize(32).expectedSize(32).create();
synchronized (this) {
for (ObjectLongPair<int[]> p : frequency.keyValuesView()) {
mostExpensive.add(new Entry(p.getOne(), p.getTwo()));
}
}
ObjectIntHashMap<int[]> postingListMapping = new ObjectIntHashMap<>();
int[] bitVector = new int[nDocuments];
int length = mostExpensive.size();
for (int i = 0; i < length; i++) {
Entry e = mostExpensive.removeFirst();
int[] docIds = e.docIds;
postingListMapping.put(docIds, i);
for (int docId : docIds) {
bitVector[docId] |= (1 << i);
}
}
return new CachedPostingListCounter(postingListMapping, bitVector);
}
int[] getBitVector() {
return bitVector;
}
ObjectIntHashMap<int[]> getPostingListMapping() {
return postingListMapping;
}
private static class Entry implements Comparable<Entry> {
public final int[] docIds;
final double cost;
private Entry(int[] docIds, long frequency) {
this.docIds = docIds;
this.cost = docIds.length * (double) frequency;
assert cost > 0;
}
@Override
public int compareTo(Entry o) {
return -Double.compare(cost, o.cost);
}
}
}
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