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 import java.util.ArrayList;
29
30 import com.google.common.base.Preconditions;
31
32 /**
33 * A filter that will only return the first KV from each row.
34 * <p>
35 * This filter can be used to more efficiently perform row count operations.
36 */
37 public class FirstKeyOnlyFilter extends FilterBase {
38 private boolean foundKV = false;
39
40 public FirstKeyOnlyFilter() {
41 }
42
43 public void reset() {
44 foundKV = false;
45 }
46
47 public ReturnCode filterKeyValue(KeyValue v) {
48 if(foundKV) return ReturnCode.NEXT_ROW;
49 foundKV = true;
50 return ReturnCode.INCLUDE;
51 }
52
53 public static Filter createFilterFromArguments(ArrayList<byte []> filterArguments) {
54 Preconditions.checkArgument(filterArguments.size() == 0,
55 "Expected 0 but got: %s", filterArguments.size());
56 return new FirstKeyOnlyFilter();
57 }
58
59 public void write(DataOutput out) throws IOException {
60 }
61
62 public void readFields(DataInput in) throws IOException {
63 }
64 }