org.apache.lucene.search.suggest.fst.FSTCompletionLookup Maven / Gradle / Ivy
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package org.apache.lucene.search.suggest.fst;
/*
* 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.
*/
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;
import org.apache.lucene.search.suggest.InputIterator;
import org.apache.lucene.search.suggest.Lookup;
import org.apache.lucene.search.suggest.Sort.SortInfo;
import org.apache.lucene.search.suggest.Sort;
import org.apache.lucene.search.suggest.fst.FSTCompletion.Completion;
import org.apache.lucene.search.suggest.tst.TSTLookup;
import org.apache.lucene.store.ByteArrayDataInput;
import org.apache.lucene.store.ByteArrayDataOutput;
import org.apache.lucene.store.DataInput;
import org.apache.lucene.store.DataOutput;
import org.apache.lucene.store.InputStreamDataInput;
import org.apache.lucene.store.OutputStreamDataOutput;
import org.apache.lucene.util.*;
import org.apache.lucene.util.fst.FST;
import org.apache.lucene.util.fst.NoOutputs;
/**
* An adapter from {@link Lookup} API to {@link FSTCompletion}.
*
* This adapter differs from {@link FSTCompletion} in that it attempts
* to discretize any "weights" as passed from in {@link InputIterator#weight()}
* to match the number of buckets. For the rationale for bucketing, see
* {@link FSTCompletion}.
*
*
Note:Discretization requires an additional sorting pass.
*
*
The range of weights for bucketing/ discretization is determined
* by sorting the input by weight and then dividing into
* equal ranges. Then, scores within each range are assigned to that bucket.
*
*
Note that this means that even large differences in weights may be lost
* during automaton construction, but the overall distinction between "classes"
* of weights will be preserved regardless of the distribution of weights.
*
*
For fine-grained control over which weights are assigned to which buckets,
* use {@link FSTCompletion} directly or {@link TSTLookup}, for example.
*
* @see FSTCompletion
* @lucene.experimental
*/
public class FSTCompletionLookup extends Lookup {
/**
* An invalid bucket count if we're creating an object
* of this class from an existing FST.
*
* @see #FSTCompletionLookup(FSTCompletion, boolean)
*/
private static int INVALID_BUCKETS_COUNT = -1;
/**
* Shared tail length for conflating in the created automaton. Setting this
* to larger values ({@link Integer#MAX_VALUE}) will create smaller (or minimal)
* automata at the cost of RAM for keeping nodes hash in the {@link FST}.
*
*
Empirical pick.
*/
private final static int sharedTailLength = 5;
private int buckets;
private boolean exactMatchFirst;
/**
* Automaton used for completions with higher weights reordering.
*/
private FSTCompletion higherWeightsCompletion;
/**
* Automaton used for normal completions.
*/
private FSTCompletion normalCompletion;
/** Number of entries the lookup was built with */
private long count = 0;
/**
* This constructor prepares for creating a suggested FST using the
* {@link #build(InputIterator)} method. The number of weight
* discretization buckets is set to {@link FSTCompletion#DEFAULT_BUCKETS} and
* exact matches are promoted to the top of the suggestions list.
*/
public FSTCompletionLookup() {
this(FSTCompletion.DEFAULT_BUCKETS, true);
}
/**
* This constructor prepares for creating a suggested FST using the
* {@link #build(InputIterator)} method.
*
* @param buckets
* The number of weight discretization buckets (see
* {@link FSTCompletion} for details).
*
* @param exactMatchFirst
* If true exact matches are promoted to the top of the
* suggestions list. Otherwise they appear in the order of
* discretized weight and alphabetical within the bucket.
*/
public FSTCompletionLookup(int buckets, boolean exactMatchFirst) {
this.buckets = buckets;
this.exactMatchFirst = exactMatchFirst;
}
/**
* This constructor takes a pre-built automaton.
*
* @param completion
* An instance of {@link FSTCompletion}.
* @param exactMatchFirst
* If true exact matches are promoted to the top of the
* suggestions list. Otherwise they appear in the order of
* discretized weight and alphabetical within the bucket.
*/
public FSTCompletionLookup(FSTCompletion completion, boolean exactMatchFirst) {
this(INVALID_BUCKETS_COUNT, exactMatchFirst);
this.normalCompletion = new FSTCompletion(
completion.getFST(), false, exactMatchFirst);
this.higherWeightsCompletion = new FSTCompletion(
completion.getFST(), true, exactMatchFirst);
}
@Override
public void build(InputIterator iterator) throws IOException {
if (iterator.hasPayloads()) {
throw new IllegalArgumentException("this suggester doesn't support payloads");
}
File tempInput = File.createTempFile(
FSTCompletionLookup.class.getSimpleName(), ".input", Sort.defaultTempDir());
File tempSorted = File.createTempFile(
FSTCompletionLookup.class.getSimpleName(), ".sorted", Sort.defaultTempDir());
Sort.ByteSequencesWriter writer = new Sort.ByteSequencesWriter(tempInput);
Sort.ByteSequencesReader reader = null;
ExternalRefSorter sorter = null;
// Push floats up front before sequences to sort them. For now, assume they are non-negative.
// If negative floats are allowed some trickery needs to be done to find their byte order.
boolean success = false;
count = 0;
try {
byte [] buffer = new byte [0];
ByteArrayDataOutput output = new ByteArrayDataOutput(buffer);
BytesRef spare;
while ((spare = iterator.next()) != null) {
if (spare.length + 4 >= buffer.length) {
buffer = ArrayUtil.grow(buffer, spare.length + 4);
}
output.reset(buffer);
output.writeInt(encodeWeight(iterator.weight()));
output.writeBytes(spare.bytes, spare.offset, spare.length);
writer.write(buffer, 0, output.getPosition());
}
writer.close();
// We don't know the distribution of scores and we need to bucket them, so we'll sort
// and divide into equal buckets.
SortInfo info = new Sort().sort(tempInput, tempSorted);
tempInput.delete();
FSTCompletionBuilder builder = new FSTCompletionBuilder(
buckets, sorter = new ExternalRefSorter(new Sort()), sharedTailLength);
final int inputLines = info.lines;
reader = new Sort.ByteSequencesReader(tempSorted);
long line = 0;
int previousBucket = 0;
int previousScore = 0;
ByteArrayDataInput input = new ByteArrayDataInput();
BytesRef tmp1 = new BytesRef();
BytesRef tmp2 = new BytesRef();
while (reader.read(tmp1)) {
input.reset(tmp1.bytes);
int currentScore = input.readInt();
int bucket;
if (line > 0 && currentScore == previousScore) {
bucket = previousBucket;
} else {
bucket = (int) (line * buckets / inputLines);
}
previousScore = currentScore;
previousBucket = bucket;
// Only append the input, discard the weight.
tmp2.bytes = tmp1.bytes;
tmp2.offset = input.getPosition();
tmp2.length = tmp1.length - input.getPosition();
builder.add(tmp2, bucket);
line++;
count++;
}
// The two FSTCompletions share the same automaton.
this.higherWeightsCompletion = builder.build();
this.normalCompletion = new FSTCompletion(
higherWeightsCompletion.getFST(), false, exactMatchFirst);
success = true;
} finally {
if (success)
IOUtils.close(reader, writer, sorter);
else
IOUtils.closeWhileHandlingException(reader, writer, sorter);
tempInput.delete();
tempSorted.delete();
}
}
/** weight -> cost */
private static int encodeWeight(long value) {
if (value < Integer.MIN_VALUE || value > Integer.MAX_VALUE) {
throw new UnsupportedOperationException("cannot encode value: " + value);
}
return (int)value;
}
@Override
public List lookup(CharSequence key, boolean higherWeightsFirst, int num) {
final List completions;
if (higherWeightsFirst) {
completions = higherWeightsCompletion.lookup(key, num);
} else {
completions = normalCompletion.lookup(key, num);
}
final ArrayList results = new ArrayList(completions.size());
CharsRef spare = new CharsRef();
for (Completion c : completions) {
spare.grow(c.utf8.length);
UnicodeUtil.UTF8toUTF16(c.utf8, spare);
results.add(new LookupResult(spare.toString(), c.bucket));
}
return results;
}
/**
* Returns the bucket (weight) as a Long for the provided key if it exists,
* otherwise null if it does not.
*/
public Object get(CharSequence key) {
final int bucket = normalCompletion.getBucket(key);
return bucket == -1 ? null : Long.valueOf(bucket);
}
@Override
public synchronized boolean store(DataOutput output) throws IOException {
output.writeVLong(count);
if (this.normalCompletion == null || normalCompletion.getFST() == null)
return false;
normalCompletion.getFST().save(output);
return true;
}
@Override
public synchronized boolean load(DataInput input) throws IOException {
count = input.readVLong();
this.higherWeightsCompletion = new FSTCompletion(new FST