Index: java/org/apache/lucene/index/SegmentTermPositions.java =================================================================== --- java/org/apache/lucene/index/SegmentTermPositions.java (revision 465175) +++ java/org/apache/lucene/index/SegmentTermPositions.java (working copy) @@ -26,6 +26,11 @@ private int proxCount; private int position; + // these variables are being used to remember information + // for a lazy skip + private long lazySkipPointer = 0; + private int lazySkipDocCount = 0; + SegmentTermPositions(SegmentReader p) { super(p); this.proxStream = (IndexInput)parent.proxStream.clone(); @@ -34,7 +39,9 @@ final void seek(TermInfo ti) throws IOException { super.seek(ti); if (ti != null) - proxStream.seek(ti.proxPointer); + lazySkipPointer = ti.proxPointer; + + lazySkipDocCount = 0; proxCount = 0; } @@ -44,22 +51,25 @@ } public final int nextPosition() throws IOException { + // perform lazy skips if neccessary + lazySkip(); proxCount--; return position += proxStream.readVInt(); } protected final void skippingDoc() throws IOException { - for (int f = freq; f > 0; f--) // skip all positions - proxStream.readVInt(); + // we remember to skip the remaining positions of the current + // document lazily + lazySkipDocCount += freq; } public final boolean next() throws IOException { - for (int f = proxCount; f > 0; f--) // skip unread positions - proxStream.readVInt(); - - if (super.next()) { // run super - proxCount = freq; // note frequency - position = 0; // reset position + // we remember to skip a document lazily + lazySkipDocCount += proxCount; + + if (super.next()) { // run super + proxCount = freq; // note frequency + position = 0; // reset position return true; } return false; @@ -72,8 +82,37 @@ /** Called by super.skipTo(). */ protected void skipProx(long proxPointer) throws IOException { - proxStream.seek(proxPointer); + // we save the pointer, we might have to skip there lazily + lazySkipPointer = proxPointer; + lazySkipDocCount = 0; proxCount = 0; } + private void skipPositions(int n) throws IOException { + for (int f = n; f > 0; f--) // skip unread positions + proxStream.readVInt(); + } + + // It is not always neccessary to move the prox pointer + // to a new document after the freq pointer has been moved. + // Consider for example a phrase query with two terms: + // the freq pointer for term 1 has to move to document x + // to answer the question if the term occurs in that document. But + // only if term 2 also matches document x, the positions have to be + // read to figure out if term 1 and term 2 appear next + // to each other in document x and thus satisfy the query. + // So we move the prox pointer lazily to the document + // as soon as positions are requested. + private void lazySkip() throws IOException { + if (lazySkipPointer != 0) { + proxStream.seek(lazySkipPointer); + lazySkipPointer = 0; + } + + if (lazySkipDocCount != 0) { + skipPositions(lazySkipDocCount); + lazySkipDocCount = 0; + } + } + } Index: test/org/apache/lucene/index/TestLazyProxSkipping.java =================================================================== --- test/org/apache/lucene/index/TestLazyProxSkipping.java (revision 0) +++ test/org/apache/lucene/index/TestLazyProxSkipping.java (revision 0) @@ -0,0 +1,150 @@ +package org.apache.lucene.index; + +/** + * Copyright 2006 The Apache Software Foundation + * + * Licensed 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.IOException; + +import org.apache.lucene.analysis.WhitespaceAnalyzer; +import org.apache.lucene.document.Document; +import org.apache.lucene.document.Field; +import org.apache.lucene.search.Hits; +import org.apache.lucene.search.IndexSearcher; +import org.apache.lucene.search.PhraseQuery; +import org.apache.lucene.search.Searcher; +import org.apache.lucene.store.Directory; +import org.apache.lucene.store.IndexInput; +import org.apache.lucene.store.RAMDirectory; + +import junit.framework.TestCase; + +/** + * Tests lazy skipping on the proximity file. + * + */ +public class TestLazyProxSkipping extends TestCase { + private Searcher searcher; + private int seeksCounter = 0; + + private String field = "tokens"; + private String term1 = "xx"; + private String term2 = "yy"; + private String term3 = "zz"; + + private void createIndex(int numHits) throws IOException { + int numDocs = 500; + + Directory directory = new RAMDirectory(); + IndexWriter writer = new IndexWriter(directory, new WhitespaceAnalyzer(), true); + + for (int i = 0; i < numDocs; i++) { + Document doc = new Document(); + String content; + if (i % (numDocs / numHits) == 0) { + // add a document that matches the query "term1 term2" + content = this.term1 + " " + this.term2; + } else if (i % 15 == 0) { + // add a document that only contains term1 + content = this.term1 + " " + this.term1; + } else { + // add a document that contains term2 but not term 1 + content = this.term3 + " " + this.term2; + } + + doc.add(new Field(this.field, content, Field.Store.YES, Field.Index.TOKENIZED)); + writer.addDocument(doc); + } + + // make sure the index has only a single segment + writer.optimize(); + writer.close(); + + // the index is a single segment, thus IndexReader.open() returns an instance of SegmentReader + SegmentReader reader = (SegmentReader) IndexReader.open(directory); + + // we decorate the proxStream with a wrapper class that allows to count the number of calls of seek() + reader.proxStream = new SeeksCountingStream(reader.proxStream); + + this.searcher = new IndexSearcher(reader); + } + + private Hits search() throws IOException { + // create PhraseQuery "term1 term2" and search + PhraseQuery pq = new PhraseQuery(); + pq.add(new Term(this.field, this.term1)); + pq.add(new Term(this.field, this.term2)); + return this.searcher.search(pq); + } + + private void performTest(int numHits) throws IOException { + createIndex(numHits); + this.seeksCounter = 0; + Hits hits = search(); + // verify that the right number of docs was found + assertEquals(numHits, hits.length()); + + // check if the number of calls of seek() does not exceed the number of hits + assertEquals(numHits, this.seeksCounter); + } + + public void testLazySkipping() throws IOException { + // test whether only the minimum amount of seeks() are performed + performTest(5); + performTest(10); + } + + + // Simply extends IndexInput in a way that we are able to count the number + // of invocations of seek() + class SeeksCountingStream extends IndexInput { + private IndexInput input; + + + SeeksCountingStream(IndexInput input) { + this.input = input; + } + + public byte readByte() throws IOException { + return this.input.readByte(); + } + + public void readBytes(byte[] b, int offset, int len) throws IOException { + this.input.readBytes(b, offset, len); + } + + public void close() throws IOException { + this.input.close(); + } + + public long getFilePointer() { + return this.input.getFilePointer(); + } + + public void seek(long pos) throws IOException { + TestLazyProxSkipping.this.seeksCounter++; + this.input.seek(pos); + } + + public long length() { + return this.input.length(); + } + + public Object clone() { + return new SeeksCountingStream((IndexInput) this.input.clone()); + } + + } +}