hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/SnapshotSegmentScanner.java

   1 /*
   2  *
   3  * Licensed to the Apache Software Foundation (ASF) under one
   4  * or more contributor license agreements.  See the NOTICE file
   5  * distributed with this work for additional information
   6  * regarding copyright ownership.  The ASF licenses this file
   7  * to you under the Apache License, Version 2.0 (the
   8  * "License"); you may not use this file except in compliance
   9  * with the License.  You may obtain a copy of the License at
  10  *
  11  *     http://www.apache.org/licenses/LICENSE-2.0
  12  *
  13  * Unless required by applicable law or agreed to in writing, software
  14  * distributed under the License is distributed on an "AS IS" BASIS,
  15  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  16  * See the License for the specific language governing permissions and
  17  * limitations under the License.
  18  */
  19 package org.apache.hadoop.hbase.regionserver;
  20
  21 import java.util.Iterator;
  22
  23 import org.apache.hadoop.hbase.Cell;
  24 import org.apache.yetus.audience.InterfaceAudience;
  25
  26
  27 /**
  28  * A basic SegmentScanner used against an ImmutableScanner snapshot
  29  * Used flushing where we do a single pass, no reverse scanning or
  30  * inserts happening. Its a dumbed-down Scanner that can go fast.
  31  * Like {@link org.apache.hadoop.hbase.util.CollectionBackedScanner}
  32  * (but making it know about Segments was onerous).
  33  */
  34 @InterfaceAudience.Private
  35 public class SnapshotSegmentScanner extends NonReversedNonLazyKeyValueScanner {
  36   private final ImmutableSegment segment;
  37   private Iterator<Cell> iter;
  38   private Cell current;
  39
  40   public SnapshotSegmentScanner(ImmutableSegment segment) {
  41     this.segment = segment;
  42     this.segment.incScannerCount();
  43     this.iter = createIterator(this.segment);
  44     if (this.iter.hasNext()){
  45       this.current = this.iter.next();
  46     }
  47   }
  48
  49   private static Iterator<Cell> createIterator(Segment segment) {
  50     return segment.getCellSet().iterator();
  51   }
  52
  53   @Override
  54   public Cell peek() {
  55     return current;
  56   }
  57
  58   @Override
  59   public Cell next() {
  60     Cell oldCurrent = current;
  61     if(iter.hasNext()){
  62       current = iter.next();
  63     } else {
  64       current = null;
  65     }
  66     return oldCurrent;
  67   }
  68
  69   @Override
  70   public boolean seek(Cell seekCell) {
  71     // restart iterator
  72     this.iter = createIterator(this.segment);
  73     return reseek(seekCell);
  74   }
  75
  76   @Override
  77   public boolean reseek(Cell seekCell) {
  78     while (this.iter.hasNext()){
  79       Cell next = this.iter.next();
  80       int ret = this.segment.getComparator().compare(next, seekCell);
  81       if (ret >= 0) {
  82         this.current = next;
  83         return true;
  84       }
  85     }
  86     return false;
  87   }
  88
  89   /**
  90    * @see KeyValueScanner#getScannerOrder()
  91    */
  92   @Override
  93   public long getScannerOrder() {
  94     return 0;
  95   }
  96
  97   @Override
  98   public void close() {
  99     this.segment.decScannerCount();
 100   }
 101 }