1 /*
2 * Copyright 2010 The Apache Software Foundation
3 *
4 * Licensed to the Apache Software Foundation (ASF) under one
5 * or more contributor license agreements. See the NOTICE file
6 * distributed with this work for additional information
7 * regarding copyright ownership. The ASF licenses this file
8 * to you under the Apache License, Version 2.0 (the
9 * "License"); you may not use this file except in compliance
10 * with the License. You may obtain a copy of the License at
11 *
12 * http://www.apache.org/licenses/LICENSE-2.0
13 *
14 * Unless required by applicable law or agreed to in writing, software
15 * distributed under the License is distributed on an "AS IS" BASIS,
16 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17 * See the License for the specific language governing permissions and
18 * limitations under the License.
19 */
20 package org.apache.hadoop.hbase.filter;
21
22 import org.apache.hadoop.hbase.KeyValue;
23
24 import java.io.DataOutput;
25 import java.io.IOException;
26 import java.io.DataInput;
27 import java.util.List;
28
29 /**
30 * A filter that will only return the first KV from each row.
31 * <p>
32 * This filter can be used to more efficiently perform row count operations.
33 */
34 public class FirstKeyOnlyFilter extends FilterBase {
35 private boolean foundKV = false;
36
37 public FirstKeyOnlyFilter() {
38 }
39
40 public void reset() {
41 foundKV = false;
42 }
43
44 public ReturnCode filterKeyValue(KeyValue v) {
45 if(foundKV) return ReturnCode.NEXT_ROW;
46 foundKV = true;
47 return ReturnCode.INCLUDE;
48 }
49
50 public void write(DataOutput out) throws IOException {
51 }
52
53 public void readFields(DataInput in) throws IOException {
54 }
55 }