1 /**
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 */
18 package org.apache.hadoop.hbase.constraint;
19
20 import org.apache.hadoop.hbase.classification.InterfaceAudience;
21 import org.apache.hadoop.conf.Configurable;
22 import org.apache.hadoop.hbase.client.Put;
23
24 /**
25 * Apply a {@link Constraint} (in traditional database terminology) to a HTable.
26 * Any number of {@link Constraint Constraints} can be added to the table, in
27 * any order.
28 * <p>
29 * A {@link Constraint} must be added to a table before the table is loaded via
30 * {@link Constraints#add(HTableDescriptor, Class...)} or
31 * {@link Constraints#add(HTableDescriptor,
32 * org.apache.hadoop.hbase.util.Pair...)}
33 * (if you want to add a configuration with the {@link Constraint}). Constraints
34 * will be run in the order that they are added. Further, a Constraint will be
35 * configured before it is run (on load).
36 * <p>
37 * See {@link Constraints#enableConstraint(HTableDescriptor, Class)} and
38 * {@link Constraints#disableConstraint(HTableDescriptor, Class)} for
39 * enabling/disabling of a given {@link Constraint} after it has been added.
40 * <p>
41 * If a {@link Put} is invalid, the Constraint should throw some sort of
42 * {@link org.apache.hadoop.hbase.constraint.ConstraintException}, indicating
43 * that the {@link Put} has failed. When
44 * this exception is thrown, not further retries of the {@link Put} are
45 * attempted nor are any other {@link Constraint Constraints} attempted (the
46 * {@link Put} is clearly not valid). Therefore, there are performance
47 * implications in the order in which {@link BaseConstraint Constraints} are
48 * specified.
49 * <p>
50 * If a {@link Constraint} fails to fail the {@link Put} via a
51 * {@link org.apache.hadoop.hbase.constraint.ConstraintException}, but instead
52 * throws a {@link RuntimeException},
53 * the entire constraint processing mechanism ({@link ConstraintProcessor}) will
54 * be unloaded from the table. This ensures that the region server is still
55 * functional, but no more {@link Put Puts} will be checked via
56 * {@link Constraint Constraints}.
57 * <p>
58 * Further, {@link Constraint Constraints} should probably not be used to
59 * enforce cross-table references as it will cause tremendous write slowdowns,
60 * but it is possible.
61 * <p>
62 * NOTE: Implementing classes must have a nullary (no-args) constructor
63 *
64 * @see BaseConstraint
65 * @see Constraints
66 */
67 @InterfaceAudience.Private
68 public interface Constraint extends Configurable {
69
70 /**
71 * Check a {@link Put} to ensure it is valid for the table. If the {@link Put}
72 * is valid, then just return from the method. Otherwise, throw an
73 * {@link Exception} specifying what happened. This {@link Exception} is
74 * propagated back to the client so you can see what caused the {@link Put} to
75 * fail.
76 * @param p {@link Put} to check
77 * @throws org.apache.hadoop.hbase.constraint.ConstraintException when the
78 * {@link Put} does not match the
79 * constraint.
80 */
81 void check(Put p) throws ConstraintException;
82
83 }