org.apache.lucene.search.FieldComparator Maven / Gradle / Ivy
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* 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
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package org.apache.lucene.search;
import java.io.IOException;
import org.apache.lucene.index.BinaryDocValues;
import org.apache.lucene.index.DocValues;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.index.SortedDocValues;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.BytesRefBuilder;
/**
* Expert: a FieldComparator compares hits so as to determine their
* sort order when collecting the top results with {@link
* TopFieldCollector}. The concrete public FieldComparator
* classes here correspond to the SortField types.
*
* The document IDs passed to these methods must only
* move forwards, since they are using doc values iterators
* to retrieve sort values.
*
* This API is designed to achieve high performance
* sorting, by exposing a tight interaction with {@link
* FieldValueHitQueue} as it visits hits. Whenever a hit is
* competitive, it's enrolled into a virtual slot, which is
* an int ranging from 0 to numHits-1. Segment transitions are
* handled by creating a dedicated per-segment
* {@link LeafFieldComparator} which also needs to interact
* with the {@link FieldValueHitQueue} but can optimize based
* on the segment to collect.
*
* The following functions need to be implemented
*
* - {@link #compare} Compare a hit at 'slot a'
* with hit 'slot b'.
*
*
- {@link #setTopValue} This method is called by
* {@link TopFieldCollector} to notify the
* FieldComparator of the top most value, which is
* used by future calls to
* {@link LeafFieldComparator#compareTop}.
*
*
- {@link #getLeafComparator(org.apache.lucene.index.LeafReaderContext)} Invoked
* when the search is switching to the next segment.
* You may need to update internal state of the
* comparator, for example retrieving new values from
* DocValues.
*
*
- {@link #value} Return the sort value stored in
* the specified slot. This is only called at the end
* of the search, in order to populate {@link
* FieldDoc#fields} when returning the top results.
*
*
* @see LeafFieldComparator
* @lucene.experimental
*/
public abstract class FieldComparator {
/**
* Compare hit at slot1 with hit at slot2.
*
* @param slot1 first slot to compare
* @param slot2 second slot to compare
* @return any {@code N < 0} if slot2's value is sorted after
* slot1, any {@code N > 0} if the slot2's value is sorted before
* slot1 and {@code 0} if they are equal
*/
public abstract int compare(int slot1, int slot2);
/**
* Record the top value, for future calls to {@link
* LeafFieldComparator#compareTop}. This is only called for searches that
* use searchAfter (deep paging), and is called before any
* calls to {@link #getLeafComparator(LeafReaderContext)}.
*/
public abstract void setTopValue(T value);
/**
* Return the actual value in the slot.
*
* @param slot the value
* @return value in this slot
*/
public abstract T value(int slot);
/**
* Get a per-segment {@link LeafFieldComparator} to collect the given
* {@link org.apache.lucene.index.LeafReaderContext}. All docIDs supplied to
* this {@link LeafFieldComparator} are relative to the current reader (you
* must add docBase if you need to map it to a top-level docID).
*
* @param context current reader context
* @return the comparator to use for this segment
* @throws IOException if there is a low-level IO error
*/
public abstract LeafFieldComparator getLeafComparator(LeafReaderContext context) throws IOException;
/** Returns a negative integer if first is less than second,
* 0 if they are equal and a positive integer otherwise. Default
* impl to assume the type implements Comparable and
* invoke .compareTo; be sure to override this method if
* your FieldComparator's type isn't a Comparable or
* if your values may sometimes be null */
@SuppressWarnings("unchecked")
public int compareValues(T first, T second) {
if (first == null) {
if (second == null) {
return 0;
} else {
return -1;
}
} else if (second == null) {
return 1;
} else {
return ((Comparable) first).compareTo(second);
}
}
/**
* Informs the comparator that sort is done on this single field.
* This is useful to enable some optimizations for skipping non-competitive documents.
*/
public void setSingleSort() {
}
/**
* Informs the comparator that the skipping of documents should be disabled.
* This function is called in cases when the skipping functionality
* should not be applied or not necessary.
*
* One example for numeric comparators is when we don't know if the same numeric data has
* been indexed with docValues and points if these two fields have the same name.
* As the skipping functionality relies on these fields to have the same data
* and as we don't know if it is true, we have to disable it.
*
* Another example could be when search sort is a part of the index sort,
* and can be already efficiently handled by TopFieldCollector,
* and doing extra work for skipping in the comparator is redundant.
*/
public void disableSkipping() {
}
/** Sorts by descending relevance. NOTE: if you are
* sorting only by descending relevance and then
* secondarily by ascending docID, performance is faster
* using {@link TopScoreDocCollector} directly (which {@link
* IndexSearcher#search} uses when no {@link Sort} is
* specified). */
public static final class RelevanceComparator extends FieldComparator implements LeafFieldComparator {
private final float[] scores;
private float bottom;
private Scorable scorer;
private float topValue;
/** Creates a new comparator based on relevance for {@code numHits}. */
public RelevanceComparator(int numHits) {
scores = new float[numHits];
}
@Override
public int compare(int slot1, int slot2) {
return Float.compare(scores[slot2], scores[slot1]);
}
@Override
public int compareBottom(int doc) throws IOException {
float score = scorer.score();
assert !Float.isNaN(score);
return Float.compare(score, bottom);
}
@Override
public void copy(int slot, int doc) throws IOException {
scores[slot] = scorer.score();
assert !Float.isNaN(scores[slot]);
}
@Override
public LeafFieldComparator getLeafComparator(LeafReaderContext context) {
return this;
}
@Override
public void setBottom(final int bottom) {
this.bottom = scores[bottom];
}
@Override
public void setTopValue(Float value) {
topValue = value;
}
@Override
public void setScorer(Scorable scorer) {
// wrap with a ScoreCachingWrappingScorer so that successive calls to
// score() will not incur score computation over and
// over again.
this.scorer = ScoreCachingWrappingScorer.wrap(scorer);
}
@Override
public Float value(int slot) {
return Float.valueOf(scores[slot]);
}
// Override because we sort reverse of natural Float order:
@Override
public int compareValues(Float first, Float second) {
// Reversed intentionally because relevance by default
// sorts descending:
return second.compareTo(first);
}
@Override
public int compareTop(int doc) throws IOException {
float docValue = scorer.score();
assert !Float.isNaN(docValue);
return Float.compare(docValue, topValue);
}
}
/** Sorts by field's natural Term sort order, using
* ordinals. This is functionally equivalent to {@link
* org.apache.lucene.search.FieldComparator.TermValComparator}, but it first resolves the string
* to their relative ordinal positions (using the index
* returned by {@link org.apache.lucene.index.LeafReader#getSortedDocValues(String)}), and
* does most comparisons using the ordinals. For medium
* to large results, this comparator will be much faster
* than {@link org.apache.lucene.search.FieldComparator.TermValComparator}. For very small
* result sets it may be slower. */
public static class TermOrdValComparator extends FieldComparator implements LeafFieldComparator {
/* Ords for each slot.
@lucene.internal */
final int[] ords;
/* Values for each slot.
@lucene.internal */
final BytesRef[] values;
private final BytesRefBuilder[] tempBRs;
/* Which reader last copied a value into the slot. When
we compare two slots, we just compare-by-ord if the
readerGen is the same; else we must compare the
values (slower).
@lucene.internal */
final int[] readerGen;
/* Gen of current reader we are on.
@lucene.internal */
int currentReaderGen = -1;
/* Current reader's doc ord/values.
@lucene.internal */
SortedDocValues termsIndex;
private final String field;
/* Bottom slot, or -1 if queue isn't full yet
@lucene.internal */
int bottomSlot = -1;
/* Bottom ord (same as ords[bottomSlot] once bottomSlot
is set). Cached for faster compares.
@lucene.internal */
int bottomOrd;
/* True if current bottom slot matches the current
reader.
@lucene.internal */
boolean bottomSameReader;
/* Bottom value (same as values[bottomSlot] once
bottomSlot is set). Cached for faster compares.
@lucene.internal */
BytesRef bottomValue;
/** Set by setTopValue. */
BytesRef topValue;
boolean topSameReader;
int topOrd;
/** -1 if missing values are sorted first, 1 if they are
* sorted last */
final int missingSortCmp;
/** Which ordinal to use for a missing value. */
final int missingOrd;
/** Creates this, sorting missing values first. */
public TermOrdValComparator(int numHits, String field) {
this(numHits, field, false);
}
/** Creates this, with control over how missing values
* are sorted. Pass sortMissingLast=true to put
* missing values at the end. */
public TermOrdValComparator(int numHits, String field, boolean sortMissingLast) {
ords = new int[numHits];
values = new BytesRef[numHits];
tempBRs = new BytesRefBuilder[numHits];
readerGen = new int[numHits];
this.field = field;
if (sortMissingLast) {
missingSortCmp = 1;
missingOrd = Integer.MAX_VALUE;
} else {
missingSortCmp = -1;
missingOrd = -1;
}
}
private int getOrdForDoc(int doc) throws IOException {
if (termsIndex.advanceExact(doc)) {
return termsIndex.ordValue();
} else {
return -1;
}
}
@Override
public int compare(int slot1, int slot2) {
if (readerGen[slot1] == readerGen[slot2]) {
return ords[slot1] - ords[slot2];
}
final BytesRef val1 = values[slot1];
final BytesRef val2 = values[slot2];
if (val1 == null) {
if (val2 == null) {
return 0;
}
return missingSortCmp;
} else if (val2 == null) {
return -missingSortCmp;
}
return val1.compareTo(val2);
}
@Override
public int compareBottom(int doc) throws IOException {
assert bottomSlot != -1;
int docOrd = getOrdForDoc(doc);
if (docOrd == -1) {
docOrd = missingOrd;
}
if (bottomSameReader) {
// ord is precisely comparable, even in the equal case
return bottomOrd - docOrd;
} else if (bottomOrd >= docOrd) {
// the equals case always means bottom is > doc
// (because we set bottomOrd to the lower bound in
// setBottom):
return 1;
} else {
return -1;
}
}
@Override
public void copy(int slot, int doc) throws IOException {
int ord = getOrdForDoc(doc);
if (ord == -1) {
ord = missingOrd;
values[slot] = null;
} else {
assert ord >= 0;
if (tempBRs[slot] == null) {
tempBRs[slot] = new BytesRefBuilder();
}
tempBRs[slot].copyBytes(termsIndex.lookupOrd(ord));
values[slot] = tempBRs[slot].get();
}
ords[slot] = ord;
readerGen[slot] = currentReaderGen;
}
/** Retrieves the SortedDocValues for the field in this segment */
protected SortedDocValues getSortedDocValues(LeafReaderContext context, String field) throws IOException {
return DocValues.getSorted(context.reader(), field);
}
@Override
public LeafFieldComparator getLeafComparator(LeafReaderContext context) throws IOException {
termsIndex = getSortedDocValues(context, field);
currentReaderGen++;
if (topValue != null) {
// Recompute topOrd/SameReader
int ord = termsIndex.lookupTerm(topValue);
if (ord >= 0) {
topSameReader = true;
topOrd = ord;
} else {
topSameReader = false;
topOrd = -ord-2;
}
} else {
topOrd = missingOrd;
topSameReader = true;
}
//System.out.println(" getLeafComparator topOrd=" + topOrd + " topSameReader=" + topSameReader);
if (bottomSlot != -1) {
// Recompute bottomOrd/SameReader
setBottom(bottomSlot);
}
return this;
}
@Override
public void setBottom(final int bottom) throws IOException {
bottomSlot = bottom;
bottomValue = values[bottomSlot];
if (currentReaderGen == readerGen[bottomSlot]) {
bottomOrd = ords[bottomSlot];
bottomSameReader = true;
} else {
if (bottomValue == null) {
// missingOrd is null for all segments
assert ords[bottomSlot] == missingOrd;
bottomOrd = missingOrd;
bottomSameReader = true;
readerGen[bottomSlot] = currentReaderGen;
} else {
final int ord = termsIndex.lookupTerm(bottomValue);
if (ord < 0) {
bottomOrd = -ord - 2;
bottomSameReader = false;
} else {
bottomOrd = ord;
// exact value match
bottomSameReader = true;
readerGen[bottomSlot] = currentReaderGen;
ords[bottomSlot] = bottomOrd;
}
}
}
}
@Override
public void setTopValue(BytesRef value) {
// null is fine: it means the last doc of the prior
// search was missing this value
topValue = value;
//System.out.println("setTopValue " + topValue);
}
@Override
public BytesRef value(int slot) {
return values[slot];
}
@Override
public int compareTop(int doc) throws IOException {
int ord = getOrdForDoc(doc);
if (ord == -1) {
ord = missingOrd;
}
if (topSameReader) {
// ord is precisely comparable, even in the equal
// case
//System.out.println("compareTop doc=" + doc + " ord=" + ord + " ret=" + (topOrd-ord));
return topOrd - ord;
} else if (ord <= topOrd) {
// the equals case always means doc is < value
// (because we set lastOrd to the lower bound)
return 1;
} else {
return -1;
}
}
@Override
public int compareValues(BytesRef val1, BytesRef val2) {
if (val1 == null) {
if (val2 == null) {
return 0;
}
return missingSortCmp;
} else if (val2 == null) {
return -missingSortCmp;
}
return val1.compareTo(val2);
}
@Override
public void setScorer(Scorable scorer) {}
}
/** Sorts by field's natural Term sort order. All
* comparisons are done using BytesRef.compareTo, which is
* slow for medium to large result sets but possibly
* very fast for very small results sets. */
public static class TermValComparator extends FieldComparator implements LeafFieldComparator {
private final BytesRef[] values;
private final BytesRefBuilder[] tempBRs;
private BinaryDocValues docTerms;
private final String field;
private BytesRef bottom;
private BytesRef topValue;
private final int missingSortCmp;
/** Sole constructor. */
public TermValComparator(int numHits, String field, boolean sortMissingLast) {
values = new BytesRef[numHits];
tempBRs = new BytesRefBuilder[numHits];
this.field = field;
missingSortCmp = sortMissingLast ? 1 : -1;
}
private BytesRef getValueForDoc(int doc) throws IOException {
if (docTerms.advanceExact(doc)) {
return docTerms.binaryValue();
} else {
return null;
}
}
@Override
public int compare(int slot1, int slot2) {
final BytesRef val1 = values[slot1];
final BytesRef val2 = values[slot2];
return compareValues(val1, val2);
}
@Override
public int compareBottom(int doc) throws IOException {
final BytesRef comparableBytes = getValueForDoc(doc);
return compareValues(bottom, comparableBytes);
}
@Override
public void copy(int slot, int doc) throws IOException {
final BytesRef comparableBytes = getValueForDoc(doc);
if (comparableBytes == null) {
values[slot] = null;
} else {
if (tempBRs[slot] == null) {
tempBRs[slot] = new BytesRefBuilder();
}
tempBRs[slot].copyBytes(comparableBytes);
values[slot] = tempBRs[slot].get();
}
}
/** Retrieves the BinaryDocValues for the field in this segment */
protected BinaryDocValues getBinaryDocValues(LeafReaderContext context, String field) throws IOException {
return DocValues.getBinary(context.reader(), field);
}
@Override
public LeafFieldComparator getLeafComparator(LeafReaderContext context) throws IOException {
docTerms = getBinaryDocValues(context, field);
return this;
}
@Override
public void setBottom(final int bottom) {
this.bottom = values[bottom];
}
@Override
public void setTopValue(BytesRef value) {
// null is fine: it means the last doc of the prior
// search was missing this value
topValue = value;
}
@Override
public BytesRef value(int slot) {
return values[slot];
}
@Override
public int compareValues(BytesRef val1, BytesRef val2) {
// missing always sorts first:
if (val1 == null) {
if (val2 == null) {
return 0;
}
return missingSortCmp;
} else if (val2 == null) {
return -missingSortCmp;
}
return val1.compareTo(val2);
}
@Override
public int compareTop(int doc) throws IOException {
return compareValues(topValue, getValueForDoc(doc));
}
@Override
public void setScorer(Scorable scorer) {}
}
}
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