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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.io.IOException;
22  import java.util.NavigableSet;
23  
24  import org.apache.hadoop.hbase.classification.InterfaceAudience;
25  import org.apache.hadoop.hbase.Cell;
26  import org.apache.hadoop.hbase.CellComparator;
27  import org.apache.hadoop.hbase.CellUtil;
28  import org.apache.hadoop.hbase.HConstants;
29  import org.apache.hadoop.hbase.regionserver.ScanQueryMatcher.MatchCode;
30  
31  /**
32   * This class is used for the tracking and enforcement of columns and numbers
33   * of versions during the course of a Get or Scan operation, when explicit
34   * column qualifiers have been asked for in the query.
35   *
36   * With a little magic (see {@link ScanQueryMatcher}), we can use this matcher
37   * for both scans and gets.  The main difference is 'next' and 'done' collapse
38   * for the scan case (since we see all columns in order), and we only reset
39   * between rows.
40   *
41   * <p>
42   * This class is utilized by {@link ScanQueryMatcher} mainly through two methods:
43   * <ul><li>{@link #checkColumn} is called when a Put satisfies all other
44   * conditions of the query.</li>
45   * <li>{@link #getNextRowOrNextColumn} is called whenever ScanQueryMatcher
46   * believes that the current column should be skipped (by timestamp, filter etc.)</li>
47   * </ul>
48   * <p>
49   * These two methods returns a 
50   * {@link org.apache.hadoop.hbase.regionserver.ScanQueryMatcher.MatchCode}
51   * to define what action should be taken.
52   * <p>
53   * This class is NOT thread-safe as queries are never multi-threaded
54   */
55  @InterfaceAudience.Private
56  public class ExplicitColumnTracker implements ColumnTracker {
57  
58    private final int maxVersions;
59    private final int minVersions;
60  
61   /**
62    * Contains the list of columns that the ExplicitColumnTracker is tracking.
63    * Each ColumnCount instance also tracks how many versions of the requested
64    * column have been returned.
65    */
66    private final ColumnCount[] columns;
67    private int index;
68    private ColumnCount column;
69    /** Keeps track of the latest timestamp included for current column.
70     * Used to eliminate duplicates. */
71    private long latestTSOfCurrentColumn;
72    private long oldestStamp;
73  
74    /**
75     * Default constructor.
76     * @param columns columns specified user in query
77     * @param minVersions minimum number of versions to keep
78     * @param maxVersions maximum versions to return per column
79     * @param oldestUnexpiredTS the oldest timestamp we are interested in,
80     *  based on TTL 
81     */
82    public ExplicitColumnTracker(NavigableSet<byte[]> columns, int minVersions,
83        int maxVersions, long oldestUnexpiredTS) {
84      this.maxVersions = maxVersions;
85      this.minVersions = minVersions;
86      this.oldestStamp = oldestUnexpiredTS;
87      this.columns = new ColumnCount[columns.size()];
88      int i=0;
89      for(byte [] column : columns) {
90        this.columns[i++] = new ColumnCount(column);
91      }
92      reset();
93    }
94  
95      /**
96     * Done when there are no more columns to match against.
97     */
98    public boolean done() {
99      return this.index >= columns.length;
100   }
101 
102   public ColumnCount getColumnHint() {
103     return this.column;
104   }
105 
106   /**
107    * {@inheritDoc}
108    */
109   @Override
110   public ScanQueryMatcher.MatchCode checkColumn(Cell cell, byte type) {
111     // delete markers should never be passed to an
112     // *Explicit*ColumnTracker
113     assert !CellUtil.isDelete(type);
114     do {
115       // No more columns left, we are done with this query
116       if(done()) {
117         return ScanQueryMatcher.MatchCode.SEEK_NEXT_ROW; // done_row
118       }
119 
120       // No more columns to match against, done with storefile
121       if(this.column == null) {
122         return ScanQueryMatcher.MatchCode.SEEK_NEXT_ROW; // done_row
123       }
124 
125       // Compare specific column to current column
126       int ret = CellComparator.compareQualifiers(cell, column.getBuffer(), column.getOffset(),
127           column.getLength());
128 
129       // Column Matches. Return include code. The caller would call checkVersions
130       // to limit the number of versions.
131       if (ret == 0) {
132         return ScanQueryMatcher.MatchCode.INCLUDE;
133       }
134 
135       resetTS();
136 
137       if (ret < 0) {
138         // The current KV is smaller than the column the ExplicitColumnTracker
139         // is interested in, so seek to that column of interest.
140         return ScanQueryMatcher.MatchCode.SEEK_NEXT_COL;
141       }
142 
143       // The current KV is bigger than the column the ExplicitColumnTracker
144       // is interested in. That means there is no more data for the column
145       // of interest. Advance the ExplicitColumnTracker state to next
146       // column of interest, and check again.
147       if (ret > 0) {
148         ++this.index;
149         if (done()) {
150           // No more to match, do not include, done with this row.
151           return ScanQueryMatcher.MatchCode.SEEK_NEXT_ROW; // done_row
152         }
153         // This is the recursive case.
154         this.column = this.columns[this.index];
155       }
156     } while(true);
157   }
158 
159   @Override
160   public ScanQueryMatcher.MatchCode checkVersions(Cell cell,
161       long timestamp, byte type, boolean ignoreCount) throws IOException {
162     assert !CellUtil.isDelete(type);
163     if (ignoreCount) return ScanQueryMatcher.MatchCode.INCLUDE;
164     // Check if it is a duplicate timestamp
165     if (sameAsPreviousTS(timestamp)) {
166       // If duplicate, skip this Key
167       return ScanQueryMatcher.MatchCode.SKIP;
168     }
169     int count = this.column.increment();
170     if (count >= maxVersions || (count >= minVersions && isExpired(timestamp))) {
171       // Done with versions for this column
172       ++this.index;
173       resetTS();
174       if (done()) {
175         // We have served all the requested columns.
176         this.column = null;
177         return ScanQueryMatcher.MatchCode.INCLUDE_AND_SEEK_NEXT_ROW;
178       }
179       // We are done with current column; advance to next column
180       // of interest.
181       this.column = this.columns[this.index];
182       return ScanQueryMatcher.MatchCode.INCLUDE_AND_SEEK_NEXT_COL;
183     }
184     setTS(timestamp);
185     return ScanQueryMatcher.MatchCode.INCLUDE;
186   }
187 
188   // Called between every row.
189   public void reset() {
190     this.index = 0;
191     this.column = this.columns[this.index];
192     for(ColumnCount col : this.columns) {
193       col.setCount(0);
194     }
195     resetTS();
196   }
197 
198   private void resetTS() {
199     latestTSOfCurrentColumn = HConstants.LATEST_TIMESTAMP;
200   }
201 
202   private void setTS(long timestamp) {
203     latestTSOfCurrentColumn = timestamp;
204   }
205 
206   private boolean sameAsPreviousTS(long timestamp) {
207     return timestamp == latestTSOfCurrentColumn;
208   }
209 
210   private boolean isExpired(long timestamp) {
211     return timestamp < oldestStamp;
212   }
213 
214   /**
215    * This method is used to inform the column tracker that we are done with
216    * this column. We may get this information from external filters or
217    * timestamp range and we then need to indicate this information to
218    * tracker. It is required only in case of ExplicitColumnTracker.
219    * @param cell
220    */
221   public void doneWithColumn(Cell cell) {
222     while (this.column != null) {
223       int compare = CellComparator.compareQualifiers(cell, column.getBuffer(), column.getOffset(),
224           column.getLength());
225       resetTS();
226       if (compare >= 0) {
227         ++this.index;
228         if (done()) {
229           // Will not hit any more columns in this storefile
230           this.column = null;
231         } else {
232           this.column = this.columns[this.index];
233         }
234         if (compare > 0) continue;
235       }
236       return;
237     }
238   }
239 
240   @Override
241   public MatchCode getNextRowOrNextColumn(Cell cell) {
242     doneWithColumn(cell);
243 
244     if (getColumnHint() == null) {
245       return MatchCode.SEEK_NEXT_ROW;
246     } else {
247       return MatchCode.SEEK_NEXT_COL;
248     }
249   }
250 
251   public boolean isDone(long timestamp) {
252     return minVersions <= 0 && isExpired(timestamp);
253   }
254 }