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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.calcite.plan;
/**
* RelOptSamplingParameters represents the parameters necessary to produce a
* sample of a relation.
*
* It's parameters are derived from the SQL 2003 TABLESAMPLE clause.
*/
public class RelOptSamplingParameters {
//~ Instance fields --------------------------------------------------------
private final boolean isBernoulli;
private final float samplingPercentage;
private final boolean isRepeatable;
private final int repeatableSeed;
//~ Constructors -----------------------------------------------------------
public RelOptSamplingParameters(
boolean isBernoulli,
float samplingPercentage,
boolean isRepeatable,
int repeatableSeed) {
this.isBernoulli = isBernoulli;
this.samplingPercentage = samplingPercentage;
this.isRepeatable = isRepeatable;
this.repeatableSeed = repeatableSeed;
}
//~ Methods ----------------------------------------------------------------
/**
* Indicates whether Bernoulli or system sampling should be performed.
* Bernoulli sampling requires the decision whether to include each row in
* the the sample to be independent across rows. System sampling allows
* implementation-dependent behavior.
*
* @return true if Bernoulli sampling is configured, false for system
* sampling
*/
public boolean isBernoulli() {
return isBernoulli;
}
/**
* Returns the sampling percentage. For Bernoulli sampling, the sampling
* percentage is the likelihood that any given row will be included in the
* sample. For system sampling, the sampling percentage indicates (roughly)
* what percentage of the rows will appear in the sample.
*
* @return the sampling percentage between 0.0 and 1.0, exclusive
*/
public float getSamplingPercentage() {
return samplingPercentage;
}
/**
* Indicates whether the sample results should be repeatable. Sample results
* are only required to repeat if no changes have been made to the
* relation's content or structure. If the sample is configured to be
* repeatable, then a user-specified seed value can be obtained via
* {@link #getRepeatableSeed()}.
*
* @return true if the sample results should be repeatable
*/
public boolean isRepeatable() {
return isRepeatable;
}
/**
* If {@link #isRepeatable()} returns true, this method returns a
* user-specified seed value. Samples of the same, unmodified relation
* should be identical if the sampling mode, sampling percentage and
* repeatable seed are the same.
*
* @return seed value for repeatable samples
*/
public int getRepeatableSeed() {
return repeatableSeed;
}
}
// End RelOptSamplingParameters.java