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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* 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,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.pig;
import java.io.IOException;
import java.util.List;
import org.apache.hadoop.mapreduce.Job;
import org.apache.pig.classification.InterfaceAudience;
import org.apache.pig.classification.InterfaceStability;
/**
* This interface defines how a loader can support predicate pushdown.
* If a given loader implements this interface, pig will pushdown predicates based on
* type of operations supported by the loader on given set of fields.
*
* This interface is private in Pig 0.14 and will be made public in Pig 0.15 after PIG-4093.
* It is to be used only by builtin LoadFunc implementations till it is made public
* as PIG-4093 will cause API changes to this interface and make it backward incompatible.
*
* @since Pig 0.14
*/
@InterfaceAudience.Private
@InterfaceStability.Evolving
public interface LoadPredicatePushdown {
/**
* Find what fields of the data can support predicate pushdown.
* @param location Location as returned by
* {@link LoadFunc#relativeToAbsolutePath(String, org.apache.hadoop.fs.Path)}
*
* @param job The {@link Job} object - this should be used only to obtain
* cluster properties through {@link Job#getConfiguration()} and not to set/query
* any runtime job information.
*
* @return list of field names that can be pushed down. Implementations
* should return null to indicate that there are no fields that support predicate pushdown
*
* @throws IOException if an exception occurs while retrieving predicate fields
*/
List<String> getPredicateFields(String location, Job job)
throws IOException;
/**
* Indicate operations on fields supported by the loader for predicate pushdown
*
* @return List of operations supported by the predicate pushdown loader
*/
List<Expression.OpType> getSupportedExpressionTypes();
/**
* Push down expression to the loader
*
* @param predicate expression to be filtered by the loader.
* @throws IOException
*/
void setPushdownPredicate(Expression predicate) throws IOException;
}