001/**
002 * Copyright The Apache Software Foundation
003 *
004 * Licensed to the Apache Software Foundation (ASF) under one or more
005 * contributor license agreements. See the NOTICE file distributed with this
006 * work for additional information regarding copyright ownership. The ASF
007 * licenses this file to you under the Apache License, Version 2.0 (the
008 * "License"); you may not use this file except in compliance with the License.
009 * You may obtain a copy of the License at
010 *
011 * http://www.apache.org/licenses/LICENSE-2.0
012 *
013 * Unless required by applicable law or agreed to in writing, software
014 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
015 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
016 * License for the specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.hadoop.hbase.regionserver;
020
021import java.io.IOException;
022import java.util.List;
023import java.util.NavigableSet;
024
025import org.apache.hadoop.hbase.Cell;
026import org.apache.hadoop.hbase.CellComparator;
027import org.apache.hadoop.hbase.CellUtil;
028import org.apache.hadoop.hbase.HConstants;
029import org.apache.hadoop.hbase.client.Scan;
030import org.apache.yetus.audience.InterfaceAudience;
031
032/**
033 * ReversedStoreScanner extends from StoreScanner, and is used to support
034 * reversed scanning.
035 */
036@InterfaceAudience.Private
037public class ReversedStoreScanner extends StoreScanner implements KeyValueScanner {
038
039  /**
040   * Opens a scanner across memstore, snapshot, and all StoreFiles. Assumes we
041   * are not in a compaction.
042   * 
043   * @param store who we scan
044   * @param scanInfo
045   * @param scan the spec
046   * @param columns which columns we are scanning
047   * @throws IOException
048   */
049  public ReversedStoreScanner(HStore store, ScanInfo scanInfo, Scan scan,
050      NavigableSet<byte[]> columns, long readPt)
051      throws IOException {
052    super(store, scanInfo, scan, columns, readPt);
053  }
054
055  /** Constructor for testing. */
056  public ReversedStoreScanner(Scan scan, ScanInfo scanInfo, NavigableSet<byte[]> columns,
057      List<? extends KeyValueScanner> scanners) throws IOException {
058    super(scan, scanInfo, columns, scanners);
059  }
060
061  @Override
062  protected void resetKVHeap(List<? extends KeyValueScanner> scanners,
063      CellComparator comparator) throws IOException {
064    // Combine all seeked scanners with a heap
065    heap = new ReversedKeyValueHeap(scanners, comparator);
066  }
067
068  @Override
069  protected void seekScanners(List<? extends KeyValueScanner> scanners,
070      Cell seekKey, boolean isLazy, boolean isParallelSeek)
071      throws IOException {
072    // Seek all scanners to the start of the Row (or if the exact matching row
073    // key does not exist, then to the start of the previous matching Row).
074    if (CellUtil.matchingRows(seekKey, HConstants.EMPTY_START_ROW)) {
075      for (KeyValueScanner scanner : scanners) {
076        scanner.seekToLastRow();
077      }
078    } else {
079      for (KeyValueScanner scanner : scanners) {
080        scanner.backwardSeek(seekKey);
081      }
082    }
083  }
084
085  @Override
086  protected boolean seekToNextRow(Cell kv) throws IOException {
087    return seekToPreviousRow(kv);
088  }
089
090  /**
091   * Do a backwardSeek in a reversed StoreScanner(scan backward)
092   */
093  @Override
094  protected boolean seekAsDirection(Cell kv) throws IOException {
095    return backwardSeek(kv);
096  }
097
098  @Override
099  protected void checkScanOrder(Cell prevKV, Cell kv,
100      CellComparator comparator) throws IOException {
101    // Check that the heap gives us KVs in an increasing order for same row and
102    // decreasing order for different rows.
103    assert prevKV == null || comparator == null || comparator.compareRows(kv, prevKV) < 0
104        || (CellUtil.matchingRows(kv, prevKV) && comparator.compare(kv,
105            prevKV) >= 0) : "Key " + prevKV
106        + " followed by a " + "error order key " + kv + " in cf " + store
107        + " in reversed scan";
108  }
109
110  @Override
111  public boolean reseek(Cell kv) throws IOException {
112    throw new IllegalStateException(
113        "reseek cannot be called on ReversedStoreScanner");
114  }
115
116  @Override
117  public boolean seek(Cell key) throws IOException {
118    throw new IllegalStateException(
119        "seek cannot be called on ReversedStoreScanner");
120  }
121
122  @Override
123  public boolean seekToPreviousRow(Cell key) throws IOException {
124    if (checkFlushed()) {
125      reopenAfterFlush();
126    }
127    return this.heap.seekToPreviousRow(key);
128  }
129
130  @Override
131  public boolean backwardSeek(Cell key) throws IOException {
132    if (checkFlushed()) {
133      reopenAfterFlush();
134    }
135    return this.heap.backwardSeek(key);
136  }
137}