Java tutorial
/* * 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. */ package org.apache.lucene.codecs.blocktree; import java.io.IOException; import java.util.ArrayList; import java.util.Arrays; import java.util.Collection; import java.util.Collections; import java.util.Iterator; import java.util.List; import java.util.Map; import java.util.TreeMap; import org.apache.lucene.codecs.CodecUtil; import org.apache.lucene.codecs.FieldsProducer; import org.apache.lucene.codecs.PostingsReaderBase; import org.apache.lucene.index.CorruptIndexException; import org.apache.lucene.index.FieldInfo; import org.apache.lucene.index.IndexFileNames; import org.apache.lucene.index.IndexOptions; import org.apache.lucene.index.SegmentReadState; import org.apache.lucene.index.Terms; import org.apache.lucene.store.IndexInput; import org.apache.lucene.util.Accountable; import org.apache.lucene.util.Accountables; import org.apache.lucene.util.BytesRef; import org.apache.lucene.util.IOUtils; import org.apache.lucene.util.fst.ByteSequenceOutputs; import org.apache.lucene.util.fst.Outputs; /** A block-based terms index and dictionary that assigns * terms to variable length blocks according to how they * share prefixes. The terms index is a prefix trie * whose leaves are term blocks. The advantage of this * approach is that seekExact is often able to * determine a term cannot exist without doing any IO, and * intersection with Automata is very fast. Note that this * terms dictionary has its own fixed terms index (ie, it * does not support a pluggable terms index * implementation). * * <p><b>NOTE</b>: this terms dictionary supports * min/maxItemsPerBlock during indexing to control how * much memory the terms index uses.</p> * * <p>The data structure used by this implementation is very * similar to a burst trie * (http://citeseer.ist.psu.edu/viewdoc/summary?doi=10.1.1.18.3499), * but with added logic to break up too-large blocks of all * terms sharing a given prefix into smaller ones.</p> * * <p>Use {@link org.apache.lucene.index.CheckIndex} with the <code>-verbose</code> * option to see summary statistics on the blocks in the * dictionary. * * See {@link BlockTreeTermsWriter}. * * @lucene.experimental */ public final class BlockTreeTermsReader extends FieldsProducer { /** * An enum that allows to control if term index FSTs are loaded into memory or read off-heap */ public enum FSTLoadMode { /** * Always read FSTs from disk. * NOTE: If this option is used the FST will be read off-heap even if buffered directory implementations * are used. */ OFF_HEAP, /** * Never read FSTs from disk ie. all fields FSTs are loaded into memory */ ON_HEAP, /** * Always read FSTs from disk. * An exception is made for ID fields in an IndexWriter context which are always loaded into memory. * This is useful to guarantee best update performance even if a non MMapDirectory is used. * NOTE: If this option is used the FST will be read off-heap even if buffered directory implementations * are used. * See {@link FSTLoadMode#AUTO} */ OPTIMIZE_UPDATES_OFF_HEAP, /** * Automatically make the decision if FSTs are read from disk depending if the segment read from an MMAPDirectory * An exception is made for ID fields in an IndexWriter context which are always loaded into memory. */ AUTO } /** Attribute key for fst mode. */ public static final String FST_MODE_KEY = "blocktree.terms.fst"; static final Outputs<BytesRef> FST_OUTPUTS = ByteSequenceOutputs.getSingleton(); static final BytesRef NO_OUTPUT = FST_OUTPUTS.getNoOutput(); static final int OUTPUT_FLAGS_NUM_BITS = 2; static final int OUTPUT_FLAGS_MASK = 0x3; static final int OUTPUT_FLAG_IS_FLOOR = 0x1; static final int OUTPUT_FLAG_HAS_TERMS = 0x2; /** Extension of terms file */ static final String TERMS_EXTENSION = "tim"; final static String TERMS_CODEC_NAME = "BlockTreeTermsDict"; /** Initial terms format. */ public static final int VERSION_START = 2; /** Auto-prefix terms have been superseded by points. */ public static final int VERSION_AUTO_PREFIX_TERMS_REMOVED = 3; /** Current terms format. */ public static final int VERSION_CURRENT = VERSION_AUTO_PREFIX_TERMS_REMOVED; /** Extension of terms index file */ static final String TERMS_INDEX_EXTENSION = "tip"; final static String TERMS_INDEX_CODEC_NAME = "BlockTreeTermsIndex"; // Open input to the main terms dict file (_X.tib) final IndexInput termsIn; // Open input to the terms index file (_X.tip) final IndexInput indexIn; //private static final boolean DEBUG = BlockTreeTermsWriter.DEBUG; // Reads the terms dict entries, to gather state to // produce DocsEnum on demand final PostingsReaderBase postingsReader; private final TreeMap<String, FieldReader> fields = new TreeMap<>(); final String segment; final int version; /** Sole constructor. */ public BlockTreeTermsReader(PostingsReaderBase postingsReader, SegmentReadState state, FSTLoadMode defaultLoadMode) throws IOException { boolean success = false; this.postingsReader = postingsReader; this.segment = state.segmentInfo.name; String termsName = IndexFileNames.segmentFileName(segment, state.segmentSuffix, TERMS_EXTENSION); try { termsIn = state.directory.openInput(termsName, state.context); version = CodecUtil.checkIndexHeader(termsIn, TERMS_CODEC_NAME, VERSION_START, VERSION_CURRENT, state.segmentInfo.getId(), state.segmentSuffix); if (version < VERSION_AUTO_PREFIX_TERMS_REMOVED) { // pre-6.2 index, records whether auto-prefix terms are enabled in the header byte b = termsIn.readByte(); if (b != 0) { throw new CorruptIndexException("Index header pretends the index has auto-prefix terms: " + b, termsIn); } } String indexName = IndexFileNames.segmentFileName(segment, state.segmentSuffix, TERMS_INDEX_EXTENSION); indexIn = state.directory.openInput(indexName, state.context); CodecUtil.checkIndexHeader(indexIn, TERMS_INDEX_CODEC_NAME, version, version, state.segmentInfo.getId(), state.segmentSuffix); CodecUtil.checksumEntireFile(indexIn); // Have PostingsReader init itself postingsReader.init(termsIn, state); // NOTE: data file is too costly to verify checksum against all the bytes on open, // but for now we at least verify proper structure of the checksum footer: which looks // for FOOTER_MAGIC + algorithmID. This is cheap and can detect some forms of corruption // such as file truncation. CodecUtil.retrieveChecksum(termsIn); // Read per-field details seekDir(termsIn); seekDir(indexIn); final FSTLoadMode fstLoadMode = getLoadMode(state.readerAttributes, FST_MODE_KEY, defaultLoadMode); final int numFields = termsIn.readVInt(); if (numFields < 0) { throw new CorruptIndexException("invalid numFields: " + numFields, termsIn); } for (int i = 0; i < numFields; ++i) { final int field = termsIn.readVInt(); final long numTerms = termsIn.readVLong(); if (numTerms <= 0) { throw new CorruptIndexException("Illegal numTerms for field number: " + field, termsIn); } final BytesRef rootCode = readBytesRef(termsIn); final FieldInfo fieldInfo = state.fieldInfos.fieldInfo(field); if (fieldInfo == null) { throw new CorruptIndexException("invalid field number: " + field, termsIn); } final long sumTotalTermFreq = termsIn.readVLong(); // when frequencies are omitted, sumDocFreq=sumTotalTermFreq and only one value is written. final long sumDocFreq = fieldInfo.getIndexOptions() == IndexOptions.DOCS ? sumTotalTermFreq : termsIn.readVLong(); final int docCount = termsIn.readVInt(); final int longsSize = termsIn.readVInt(); if (longsSize < 0) { throw new CorruptIndexException( "invalid longsSize for field: " + fieldInfo.name + ", longsSize=" + longsSize, termsIn); } BytesRef minTerm = readBytesRef(termsIn); BytesRef maxTerm = readBytesRef(termsIn); if (docCount < 0 || docCount > state.segmentInfo.maxDoc()) { // #docs with field must be <= #docs throw new CorruptIndexException( "invalid docCount: " + docCount + " maxDoc: " + state.segmentInfo.maxDoc(), termsIn); } if (sumDocFreq < docCount) { // #postings must be >= #docs with field throw new CorruptIndexException("invalid sumDocFreq: " + sumDocFreq + " docCount: " + docCount, termsIn); } if (sumTotalTermFreq < sumDocFreq) { // #positions must be >= #postings throw new CorruptIndexException( "invalid sumTotalTermFreq: " + sumTotalTermFreq + " sumDocFreq: " + sumDocFreq, termsIn); } final FSTLoadMode perFieldLoadMode = getLoadMode(state.readerAttributes, FST_MODE_KEY + "." + fieldInfo.name, fstLoadMode); final long indexStartFP = indexIn.readVLong(); FieldReader previous = fields.put(fieldInfo.name, new FieldReader(this, fieldInfo, numTerms, rootCode, sumTotalTermFreq, sumDocFreq, docCount, indexStartFP, longsSize, indexIn, minTerm, maxTerm, state.openedFromWriter, perFieldLoadMode)); if (previous != null) { throw new CorruptIndexException("duplicate field: " + fieldInfo.name, termsIn); } } success = true; } finally { if (!success) { // this.close() will close in: IOUtils.closeWhileHandlingException(this); } } } private static FSTLoadMode getLoadMode(Map<String, String> attributes, String key, FSTLoadMode defaultValue) { String value = attributes.get(key); if (value == null) { return defaultValue; } try { return FSTLoadMode.valueOf(value); } catch (IllegalArgumentException ex) { throw new IllegalArgumentException("Invalid value for " + key + " expected one of: " + Arrays.toString(FSTLoadMode.values()) + " but was: " + value, ex); } } private static BytesRef readBytesRef(IndexInput in) throws IOException { int numBytes = in.readVInt(); if (numBytes < 0) { throw new CorruptIndexException("invalid bytes length: " + numBytes, in); } BytesRef bytes = new BytesRef(); bytes.length = numBytes; bytes.bytes = new byte[numBytes]; in.readBytes(bytes.bytes, 0, numBytes); return bytes; } /** Seek {@code input} to the directory offset. */ private static void seekDir(IndexInput input) throws IOException { input.seek(input.length() - CodecUtil.footerLength() - 8); long offset = input.readLong(); input.seek(offset); } // for debugging // private static String toHex(int v) { // return "0x" + Integer.toHexString(v); // } @Override public void close() throws IOException { try { IOUtils.close(indexIn, termsIn, postingsReader); } finally { // Clear so refs to terms index is GCable even if // app hangs onto us: fields.clear(); } } @Override public Iterator<String> iterator() { return Collections.unmodifiableSet(fields.keySet()).iterator(); } @Override public Terms terms(String field) throws IOException { assert field != null; return fields.get(field); } @Override public int size() { return fields.size(); } // for debugging String brToString(BytesRef b) { if (b == null) { return "null"; } else { try { return b.utf8ToString() + " " + b; } catch (Throwable t) { // If BytesRef isn't actually UTF8, or it's eg a // prefix of UTF8 that ends mid-unicode-char, we // fallback to hex: return b.toString(); } } } @Override public long ramBytesUsed() { long sizeInBytes = postingsReader.ramBytesUsed(); for (FieldReader reader : fields.values()) { sizeInBytes += reader.ramBytesUsed(); } return sizeInBytes; } @Override public Collection<Accountable> getChildResources() { List<Accountable> resources = new ArrayList<>(); resources.addAll(Accountables.namedAccountables("field", fields)); resources.add(Accountables.namedAccountable("delegate", postingsReader)); return Collections.unmodifiableList(resources); } @Override public void checkIntegrity() throws IOException { // term dictionary CodecUtil.checksumEntireFile(termsIn); // postings postingsReader.checkIntegrity(); } @Override public String toString() { return getClass().getSimpleName() + "(fields=" + fields.size() + ",delegate=" + postingsReader + ")"; } }