001/* 002 * Licensed to the Apache Software Foundation (ASF) under one 003 * or more contributor license agreements. See the NOTICE file 004 * distributed with this work for additional information 005 * regarding copyright ownership. The ASF licenses this file 006 * to you under the Apache License, Version 2.0 (the 007 * "License"); you may not use this file except in compliance 008 * with the License. You may obtain a copy of the License at 009 * 010 * http://www.apache.org/licenses/LICENSE-2.0 011 * 012 * Unless required by applicable law or agreed to in writing, software 013 * distributed under the License is distributed on an "AS IS" BASIS, 014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 015 * See the License for the specific language governing permissions and 016 * limitations under the License. 017 */ 018package org.apache.hadoop.hbase.regionserver; 019 020import java.io.IOException; 021import java.util.List; 022import java.util.NavigableSet; 023import org.apache.hadoop.hbase.Cell; 024import org.apache.hadoop.hbase.CellComparator; 025import org.apache.hadoop.hbase.CellUtil; 026import org.apache.hadoop.hbase.HConstants; 027import org.apache.hadoop.hbase.client.Scan; 028import org.apache.yetus.audience.InterfaceAudience; 029 030/** 031 * ReversedStoreScanner extends from StoreScanner, and is used to support reversed scanning. 032 */ 033@InterfaceAudience.Private 034public class ReversedStoreScanner extends StoreScanner implements KeyValueScanner { 035 036 /** 037 * Opens a scanner across memstore, snapshot, and all StoreFiles. Assumes we are not in a 038 * compaction. 039 * @param store who we scan n * @param scan the spec 040 * @param columns which columns we are scanning n 041 */ 042 public ReversedStoreScanner(HStore store, ScanInfo scanInfo, Scan scan, 043 NavigableSet<byte[]> columns, long readPt) throws IOException { 044 super(store, scanInfo, scan, columns, readPt); 045 } 046 047 /** Constructor for testing. */ 048 public ReversedStoreScanner(Scan scan, ScanInfo scanInfo, NavigableSet<byte[]> columns, 049 List<? extends KeyValueScanner> scanners) throws IOException { 050 super(scan, scanInfo, columns, scanners); 051 } 052 053 @Override 054 protected KeyValueHeap newKVHeap(List<? extends KeyValueScanner> scanners, 055 CellComparator comparator) throws IOException { 056 return new ReversedKeyValueHeap(scanners, comparator); 057 } 058 059 @Override 060 protected void seekScanners(List<? extends KeyValueScanner> scanners, Cell seekKey, 061 boolean isLazy, boolean isParallelSeek) throws IOException { 062 // Seek all scanners to the start of the Row (or if the exact matching row 063 // key does not exist, then to the start of the previous matching Row). 064 if (CellUtil.matchingRows(seekKey, HConstants.EMPTY_START_ROW)) { 065 for (KeyValueScanner scanner : scanners) { 066 scanner.seekToLastRow(); 067 } 068 } else { 069 for (KeyValueScanner scanner : scanners) { 070 scanner.backwardSeek(seekKey); 071 } 072 } 073 } 074 075 @Override 076 protected boolean seekToNextRow(Cell kv) throws IOException { 077 return seekToPreviousRow(kv); 078 } 079 080 /** 081 * Do a backwardSeek in a reversed StoreScanner(scan backward) 082 */ 083 @Override 084 protected boolean seekAsDirection(Cell kv) throws IOException { 085 return backwardSeek(kv); 086 } 087 088 @Override 089 protected void checkScanOrder(Cell prevKV, Cell kv, CellComparator comparator) 090 throws IOException { 091 // Check that the heap gives us KVs in an increasing order for same row and 092 // decreasing order for different rows. 093 assert prevKV == null || comparator == null || comparator.compareRows(kv, prevKV) < 0 094 || (CellUtil.matchingRows(kv, prevKV) && comparator.compare(kv, prevKV) >= 0) 095 : "Key " + prevKV + " followed by a " + "error order key " + kv + " in cf " + store 096 + " in reversed scan"; 097 } 098 099 @Override 100 public boolean reseek(Cell kv) throws IOException { 101 throw new IllegalStateException("reseek cannot be called on ReversedStoreScanner"); 102 } 103 104 @Override 105 public boolean seek(Cell key) throws IOException { 106 throw new IllegalStateException("seek cannot be called on ReversedStoreScanner"); 107 } 108 109 @Override 110 public boolean seekToPreviousRow(Cell key) throws IOException { 111 if (checkFlushed()) { 112 reopenAfterFlush(); 113 } 114 return this.heap.seekToPreviousRow(key); 115 } 116 117 @Override 118 public boolean backwardSeek(Cell key) throws IOException { 119 if (checkFlushed()) { 120 reopenAfterFlush(); 121 } 122 return this.heap.backwardSeek(key); 123 } 124}