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* Licensed to the Apache Software Foundation (ASF) under one
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* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.hbase.constraint;
import org.apache.hadoop.conf.Configurable;
import org.apache.hadoop.hbase.client.Put;
import org.apache.yetus.audience.InterfaceAudience;
/**
* Apply a {@link Constraint} (in traditional database terminology) to a HTable. Any number of
* {@link Constraint Constraints} can be added to the table, in any order.
*
* A {@link Constraint} must be added to a table before the table is loaded via
* {@link Constraints#add(org.apache.hadoop.hbase.HTableDescriptor, Class[])} or
* {@link Constraints#add(org.apache.hadoop.hbase.HTableDescriptor, org.apache.hadoop.hbase.util.Pair...)}
* (if you want to add a configuration with the {@link Constraint}). Constraints will be run in the
* order that they are added. Further, a Constraint will be configured before it is run (on load).
*
* See {@link Constraints#enableConstraint(org.apache.hadoop.hbase.HTableDescriptor, Class)} and
* {@link Constraints#disableConstraint(org.apache.hadoop.hbase.HTableDescriptor, Class)} for
* enabling/disabling of a given {@link Constraint} after it has been added.
*
* If a {@link Put} is invalid, the Constraint should throw some sort of
* {@link org.apache.hadoop.hbase.constraint.ConstraintException}, indicating that the {@link Put}
* has failed. When this exception is thrown, not further retries of the {@link Put} are attempted
* nor are any other {@link Constraint Constraints} attempted (the {@link Put} is clearly not
* valid). Therefore, there are performance implications in the order in which {@link BaseConstraint
* Constraints} are specified.
*
* If a {@link Constraint} fails to fail the {@link Put} via a
* {@link org.apache.hadoop.hbase.constraint.ConstraintException}, but instead throws a
* {@link RuntimeException}, the entire constraint processing mechanism
* ({@link ConstraintProcessor}) will be unloaded from the table. This ensures that the region
* server is still functional, but no more {@link Put Puts} will be checked via {@link Constraint
* Constraints}.
*
* Further, {@link Constraint Constraints} should probably not be used to enforce cross-table
* references as it will cause tremendous write slowdowns, but it is possible.
*
* NOTE: Implementing classes must have a nullary (no-args) constructor
* @see BaseConstraint
* @see Constraints
*/
@InterfaceAudience.Private
public interface Constraint extends Configurable {
/**
* Check a {@link Put} to ensure it is valid for the table. If the {@link Put} is valid, then just
* return from the method. Otherwise, throw an {@link Exception} specifying what happened. This
* {@link Exception} is propagated back to the client so you can see what caused the {@link Put}
* to fail.
* @param p {@link Put} to check
* @throws org.apache.hadoop.hbase.constraint.ConstraintException when the {@link Put} does not
* match the constraint.
*/
void check(Put p) throws ConstraintException;
}