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.ExtendedCell; 027import org.apache.hadoop.hbase.HConstants; 028import org.apache.hadoop.hbase.client.Scan; 029import org.apache.yetus.audience.InterfaceAudience; 030 031/** 032 * ReversedStoreScanner extends from StoreScanner, and is used to support reversed scanning. 033 */ 034@InterfaceAudience.Private 035public class ReversedStoreScanner extends StoreScanner implements KeyValueScanner { 036 037 /** 038 * Opens a scanner across memstore, snapshot, and all StoreFiles. Assumes we are not in a 039 * compaction. 040 * @param store who we scan 041 * @param scan the spec 042 * @param columns which columns we are scanning 043 */ 044 public ReversedStoreScanner(HStore store, ScanInfo scanInfo, Scan scan, 045 NavigableSet<byte[]> columns, long readPt) throws IOException { 046 super(store, scanInfo, scan, columns, readPt); 047 } 048 049 /** Constructor for testing. */ 050 public ReversedStoreScanner(Scan scan, ScanInfo scanInfo, NavigableSet<byte[]> columns, 051 List<? extends KeyValueScanner> scanners) throws IOException { 052 super(scan, scanInfo, columns, scanners); 053 } 054 055 @Override 056 protected KeyValueHeap newKVHeap(List<? extends KeyValueScanner> scanners, 057 CellComparator comparator) throws IOException { 058 return new ReversedKeyValueHeap(scanners, comparator); 059 } 060 061 @Override 062 protected void seekScanners(List<? extends KeyValueScanner> scanners, ExtendedCell seekKey, 063 boolean isLazy, boolean isParallelSeek) throws IOException { 064 // Seek all scanners to the start of the Row (or if the exact matching row 065 // key does not exist, then to the start of the previous matching Row). 066 if (CellUtil.matchingRows(seekKey, HConstants.EMPTY_START_ROW)) { 067 for (KeyValueScanner scanner : scanners) { 068 scanner.seekToLastRow(); 069 } 070 } else { 071 for (KeyValueScanner scanner : scanners) { 072 scanner.backwardSeek(seekKey); 073 } 074 } 075 } 076 077 @Override 078 protected boolean seekToNextRow(ExtendedCell kv) throws IOException { 079 return seekToPreviousRow(kv); 080 } 081 082 /** 083 * Do a backwardSeek in a reversed StoreScanner(scan backward) 084 */ 085 @Override 086 protected boolean seekAsDirection(ExtendedCell kv) throws IOException { 087 return backwardSeek(kv); 088 } 089 090 @Override 091 protected void checkScanOrder(Cell prevKV, Cell kv, CellComparator comparator) 092 throws IOException { 093 // Check that the heap gives us KVs in an increasing order for same row and 094 // decreasing order for different rows. 095 assert prevKV == null || comparator == null || comparator.compareRows(kv, prevKV) < 0 096 || (CellUtil.matchingRows(kv, prevKV) && comparator.compare(kv, prevKV) >= 0) 097 : "Key " + prevKV + " followed by a " + "error order key " + kv + " in cf " + store 098 + " in reversed scan"; 099 } 100 101 @Override 102 public boolean reseek(ExtendedCell kv) throws IOException { 103 throw new IllegalStateException("reseek cannot be called on ReversedStoreScanner"); 104 } 105 106 @Override 107 public boolean seek(ExtendedCell key) throws IOException { 108 throw new IllegalStateException("seek cannot be called on ReversedStoreScanner"); 109 } 110 111 @Override 112 public boolean seekToPreviousRow(ExtendedCell key) throws IOException { 113 if (checkFlushed()) { 114 reopenAfterFlush(); 115 } 116 return this.heap.seekToPreviousRow(key); 117 } 118 119 @Override 120 public boolean backwardSeek(ExtendedCell key) throws IOException { 121 if (checkFlushed()) { 122 reopenAfterFlush(); 123 } 124 return this.heap.backwardSeek(key); 125 } 126}