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LUCENE-5033: SlowFuzzyQuery was accepting too many documents when provided minSimilarity is an int > 1 

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1491088 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Michael McCandless 2013-06-08 22:49:47 +00:00
parent 92ec6ec337
commit b9dc8ef8f6
3 changed files with 96 additions and 56 deletions
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3
lucene/CHANGES.txt
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@ -138,6 +138,9 @@ Bug Fixes
* LUCENE-4933: SweetSpotSimilarity didn't apply its tf function to some
queries (SloppyPhraseQuery, SpanQueries). (Robert Muir)
* LUCENE-5033: SlowFuzzyQuery was accepting too many terms (documents) when
provided minSimilarity is an int > 1 (Tim Allison via Mike McCandless)
Optimizations
* LUCENE-4936: Improve numeric doc values compression in case all values share

91
lucene/sandbox/src/java/org/apache/lucene/sandbox/queries/SlowFuzzyTermsEnum.java
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@ -31,9 +31,12 @@ import org.apache.lucene.util.IntsRef;
import org.apache.lucene.util.StringHelper;
import org.apache.lucene.util.UnicodeUtil;
/** Classic fuzzy TermsEnum for enumerating all terms that are similar
/** Potentially slow fuzzy TermsEnum for enumerating all terms that are similar
* to the specified filter term.
*
* <p> If the minSimilarity or maxEdits is greater than the Automaton's
* allowable range, this backs off to the classic (brute force)
* fuzzy terms enum method by calling FuzzyTermsEnum's getAutomatonEnum.
* </p>
* <p>Term enumerations are always ordered by
* {@link #getComparator}. Each term in the enumeration is
* greater than all that precede it.</p>
@ -103,18 +106,43 @@ public final class SlowFuzzyTermsEnum extends FuzzyTermsEnum {
private final IntsRef utf32 = new IntsRef(20);
/**
* The termCompare method in FuzzyTermEnum uses Levenshtein distance to
* <p>The termCompare method in FuzzyTermEnum uses Levenshtein distance to
* calculate the distance between the given term and the comparing term.
* </p>
* <p>If the minSimilarity is >= 1.0, this uses the maxEdits as the comparison.
* Otherwise, this method uses the following logic to calculate similarity.
* <pre>
* similarity = 1 - ((float)distance / (float) (prefixLength + Math.min(textlen, targetlen)));
* </pre>
* where distance is the Levenshtein distance for the two words.
* </p>
*
*/
@Override
protected final AcceptStatus accept(BytesRef term) {
if (StringHelper.startsWith(term, prefixBytesRef)) {
UnicodeUtil.UTF8toUTF32(term, utf32);
final float similarity = similarity(utf32.ints, realPrefixLength, utf32.length - realPrefixLength);
if (similarity > minSimilarity) {
final int distance = calcDistance(utf32.ints, realPrefixLength, utf32.length - realPrefixLength);
//Integer.MIN_VALUE is the sentinel that Levenshtein stopped early
if (distance == Integer.MIN_VALUE){
return AcceptStatus.NO;
}
//no need to calc similarity, if raw is true and distance > maxEdits
if (raw == true && distance > maxEdits){
return AcceptStatus.NO;
}
final float similarity = calcSimilarity(distance, (utf32.length - realPrefixLength), text.length);
//if raw is true, then distance must also be <= maxEdits by now
//given the previous if statement
if (raw == true ||
(raw == false && similarity > minSimilarity)) {
boostAtt.setBoost((similarity - minSimilarity) * scale_factor);
return AcceptStatus.YES;
} else return AcceptStatus.NO;
} else {
return AcceptStatus.NO;
}
} else {
return AcceptStatus.END;
}
@ -125,52 +153,34 @@ public final class SlowFuzzyTermsEnum extends FuzzyTermsEnum {
******************************/
/**
* <p>Similarity returns a number that is 1.0f or less (including negative numbers)
* based on how similar the Term is compared to a target term. It returns
* exactly 0.0f when
* <pre>
* editDistance &gt; maximumEditDistance</pre>
* Otherwise it returns:
* <pre>
* 1 - (editDistance / length)</pre>
* where length is the length of the shortest term (text or target) including a
* prefix that are identical and editDistance is the Levenshtein distance for
* the two words.</p>
*
* <p>calcDistance returns the Levenshtein distance between the query term
* and the target term.</p>
*
* <p>Embedded within this algorithm is a fail-fast Levenshtein distance
* algorithm. The fail-fast algorithm differs from the standard Levenshtein
* distance algorithm in that it is aborted if it is discovered that the
* minimum distance between the words is greater than some threshold.
*
* <p>To calculate the maximum distance threshold we use the following formula:
* <pre>
* (1 - minimumSimilarity) * length</pre>
* where length is the shortest term including any prefix that is not part of the
* similarity comparison. This formula was derived by solving for what maximum value
* of distance returns false for the following statements:
* <pre>
* similarity = 1 - ((float)distance / (float) (prefixLength + Math.min(textlen, targetlen)));
* return (similarity > minimumSimilarity);</pre>
* where distance is the Levenshtein distance for the two words.
* </p>
* <p>Levenshtein distance (also known as edit distance) is a measure of similarity
* between two strings where the distance is measured as the number of character
* deletions, insertions or substitutions required to transform one string to
* the other string.
* @param target the target word or phrase
* @return the similarity, 0.0 or less indicates that it matches less than the required
* threshold and 1.0 indicates that the text and target are identical
* @param offset the offset at which to start the comparison
* @param length the length of what's left of the string to compare
* @return the number of edits or Integer.MIN_VALUE if the edit distance is
* greater than maxDistance.
*/
private final float similarity(final int[] target, int offset, int length) {
private final int calcDistance(final int[] target, int offset, int length) {
final int m = length;
final int n = text.length;
if (n == 0) {
//we don't have anything to compare. That means if we just add
//the letters for m we get the new word
return realPrefixLength == 0 ? 0.0f : 1.0f - ((float) m / realPrefixLength);
return m;
}
if (m == 0) {
return realPrefixLength == 0 ? 0.0f : 1.0f - ((float) n / realPrefixLength);
return n;
}
final int maxDistance = calculateMaxDistance(m);
@ -183,7 +193,7 @@ public final class SlowFuzzyTermsEnum extends FuzzyTermsEnum {
//which is 8-3 or more precisely Math.abs(3-8).
//if our maximum edit distance is 4, then we can discard this word
//without looking at it.
return Float.NEGATIVE_INFINITY;
return Integer.MIN_VALUE;
}
// init matrix d
@ -214,7 +224,7 @@ public final class SlowFuzzyTermsEnum extends FuzzyTermsEnum {
if (j > maxDistance && bestPossibleEditDistance > maxDistance) { //equal is okay, but not greater
//the closest the target can be to the text is just too far away.
//this target is leaving the party early.
return Float.NEGATIVE_INFINITY;
return Integer.MIN_VALUE;
}
// copy current distance counts to 'previous row' distance counts: swap p and d
@ -226,12 +236,17 @@ public final class SlowFuzzyTermsEnum extends FuzzyTermsEnum {
// our last action in the above loop was to switch d and p, so p now
// actually has the most recent cost counts
return p[n];
}
private float calcSimilarity(int edits, int m, int n){
// this will return less than 0.0 when the edit distance is
// greater than the number of characters in the shorter word.
// but this was the formula that was previously used in FuzzyTermEnum,
// so it has not been changed (even though minimumSimilarity must be
// greater than 0.0)
return 1.0f - ((float)p[n] / (float) (realPrefixLength + Math.min(n, m)));
return 1.0f - ((float)edits / (float) (realPrefixLength + Math.min(n, m)));
}
/**

58
lucene/sandbox/src/test/org/apache/lucene/sandbox/queries/TestSlowFuzzyQuery.java
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@ -43,6 +43,9 @@ import org.apache.lucene.util.LuceneTestCase;
public class TestSlowFuzzyQuery extends LuceneTestCase {
public void testFuzziness() throws Exception {
//every test with SlowFuzzyQuery.defaultMinSimilarity
//is exercising the Automaton, not the brute force linear method
Directory directory = newDirectory();
RandomIndexWriter writer = new RandomIndexWriter(random(), directory);
addDoc("aaaaa", writer);
@ -194,6 +197,30 @@ public class TestSlowFuzzyQuery extends LuceneTestCase {
directory.close();
}
public void testFuzzinessLong2() throws Exception {
//Lucene-5033
Directory directory = newDirectory();
RandomIndexWriter writer = new RandomIndexWriter(random(), directory);
addDoc("abcdef", writer);
addDoc("segment", writer);
IndexReader reader = writer.getReader();
IndexSearcher searcher = newSearcher(reader);
writer.close();
SlowFuzzyQuery query;
query = new SlowFuzzyQuery(new Term("field", "abcxxxx"), 3f, 0);
ScoreDoc[] hits = searcher.search(query, null, 1000).scoreDocs;
assertEquals(0, hits.length);
query = new SlowFuzzyQuery(new Term("field", "abcxxxx"), 4f, 0);
hits = searcher.search(query, null, 1000).scoreDocs;
assertEquals(1, hits.length);
reader.close();
directory.close();
}
public void testFuzzinessLong() throws Exception {
Directory directory = newDirectory();
RandomIndexWriter writer = new RandomIndexWriter(random(), directory);
@ -385,7 +412,6 @@ public class TestSlowFuzzyQuery extends LuceneTestCase {
public void testGiga() throws Exception {
MockAnalyzer analyzer = new MockAnalyzer(random());
Directory index = newDirectory();
RandomIndexWriter w = new RandomIndexWriter(random(), index);
@ -440,25 +466,21 @@ public class TestSlowFuzzyQuery extends LuceneTestCase {
assertEquals(1, hits.length);
assertEquals("foobar", searcher.doc(hits[0].doc).get("field"));
// TODO: cannot really be supported given the legacy scoring
// system which scores negative, if the distance > min term len,
// so such matches were always impossible with lucene 3.x, etc
//
//q = new SlowFuzzyQuery(new Term("field", "t"), 3);
//hits = searcher.search(q, 10).scoreDocs;
//assertEquals(1, hits.length);
//assertEquals("test", searcher.doc(hits[0].doc).get("field"));
q = new SlowFuzzyQuery(new Term("field", "t"), 3);
hits = searcher.search(q, 10).scoreDocs;
assertEquals(1, hits.length);
assertEquals("test", searcher.doc(hits[0].doc).get("field"));
// q = new SlowFuzzyQuery(new Term("field", "a"), 4f, 0, 50);
// hits = searcher.search(q, 10).scoreDocs;
// assertEquals(1, hits.length);
// assertEquals("test", searcher.doc(hits[0].doc).get("field"));
q = new SlowFuzzyQuery(new Term("field", "a"), 4f, 0, 50);
hits = searcher.search(q, 10).scoreDocs;
assertEquals(1, hits.length);
assertEquals("test", searcher.doc(hits[0].doc).get("field"));
// q = new SlowFuzzyQuery(new Term("field", "a"), 6f, 0, 50);
// hits = searcher.search(q, 10).scoreDocs;
// assertEquals(2, hits.length);
// assertEquals("test", searcher.doc(hits[0].doc).get("field"));
// assertEquals("foobar", searcher.doc(hits[1].doc).get("field"));
q = new SlowFuzzyQuery(new Term("field", "a"), 6f, 0, 50);
hits = searcher.search(q, 10).scoreDocs;
assertEquals(2, hits.length);
assertEquals("test", searcher.doc(hits[0].doc).get("field"));
assertEquals("foobar", searcher.doc(hits[1].doc).get("field"));
reader.close();
index.close();