package org.apache.lucene.index;
/**
* 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.IOException;
import java.util.Arrays;
import org.apache.lucene.store.IndexOutput;
/**
* Implements the skip list writer for the default posting list format
* that stores positions and payloads.
*
*/
class DefaultSkipListWriter extends MultiLevelSkipListWriter {
private int[] lastSkipDoc;
private int[] lastSkipPayloadLength;
private long[] lastSkipFreqPointer;
private long[] lastSkipProxPointer;
private IndexOutput freqOutput;
private IndexOutput proxOutput;
private int curDoc;
private boolean curStorePayloads;
private int curPayloadLength;
private long curFreqPointer;
private long curProxPointer;
DefaultSkipListWriter(int skipInterval, int numberOfSkipLevels, int docCount, IndexOutput freqOutput, IndexOutput proxOutput) {
super(skipInterval, numberOfSkipLevels, docCount);
this.freqOutput = freqOutput;
this.proxOutput = proxOutput;
lastSkipDoc = new int[numberOfSkipLevels];
lastSkipPayloadLength = new int[numberOfSkipLevels];
lastSkipFreqPointer = new long[numberOfSkipLevels];
lastSkipProxPointer = new long[numberOfSkipLevels];
}
void setFreqOutput(IndexOutput freqOutput) {
this.freqOutput = freqOutput;
}
void setProxOutput(IndexOutput proxOutput) {
this.proxOutput = proxOutput;
}
/**
* Sets the values for the current skip data.
*/
void setSkipData(int doc, boolean storePayloads, int payloadLength) {
this.curDoc = doc;
this.curStorePayloads = storePayloads;
this.curPayloadLength = payloadLength;
this.curFreqPointer = freqOutput.getFilePointer();
if (proxOutput != null)
this.curProxPointer = proxOutput.getFilePointer();
}
protected void resetSkip() {
super.resetSkip();
Arrays.fill(lastSkipDoc, 0);
Arrays.fill(lastSkipPayloadLength, -1); // we don't have to write the first length in the skip list
Arrays.fill(lastSkipFreqPointer, freqOutput.getFilePointer());
if (proxOutput != null)
Arrays.fill(lastSkipProxPointer, proxOutput.getFilePointer());
}
protected void writeSkipData(int level, IndexOutput skipBuffer) throws IOException {
// To efficiently store payloads in the posting lists we do not store the length of
// every payload. Instead we omit the length for a payload if the previous payload had
// the same length.
// However, in order to support skipping the payload length at every skip point must be known.
// So we use the same length encoding that we use for the posting lists for the skip data as well:
// Case 1: current field does not store payloads
// SkipDatum --> DocSkip, FreqSkip, ProxSkip
// DocSkip,FreqSkip,ProxSkip --> VInt
// DocSkip records the document number before every SkipInterval th document in TermFreqs.
// Document numbers are represented as differences from the previous value in the sequence.
// Case 2: current field stores payloads
// SkipDatum --> DocSkip, PayloadLength?, FreqSkip,ProxSkip
// DocSkip,FreqSkip,ProxSkip --> VInt
// PayloadLength --> VInt
// In this case DocSkip/2 is the difference between
// the current and the previous value. If DocSkip
// is odd, then a PayloadLength encoded as VInt follows,
// if DocSkip is even, then it is assumed that the
// current payload length equals the length at the previous
// skip point
if (curStorePayloads) {
int delta = curDoc - lastSkipDoc[level];
if (curPayloadLength == lastSkipPayloadLength[level]) {
// the current payload length equals the length at the previous skip point,
// so we don't store the length again
skipBuffer.writeVInt(delta * 2);
} else {
// the payload length is different from the previous one. We shift the DocSkip,
// set the lowest bit and store the current payload length as VInt.
skipBuffer.writeVInt(delta * 2 + 1);
skipBuffer.writeVInt(curPayloadLength);
lastSkipPayloadLength[level] = curPayloadLength;
}
} else {
// current field does not store payloads
skipBuffer.writeVInt(curDoc - lastSkipDoc[level]);
}
skipBuffer.writeVInt((int) (curFreqPointer - lastSkipFreqPointer[level]));
skipBuffer.writeVInt((int) (curProxPointer - lastSkipProxPointer[level]));
lastSkipDoc[level] = curDoc;
//System.out.println("write doc at level " + level + ": " + curDoc);
lastSkipFreqPointer[level] = curFreqPointer;
lastSkipProxPointer[level] = curProxPointer;
}
}