package com.mapr.synth.samplers;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.node.IntNode;
import com.google.common.base.Preconditions;
import org.apache.mahout.math.random.Multinomial;
/**
* Samples from a "foreign key" which is really just an integer.
* <p/>
* The only cleverness here is that we allow a variable amount of key skew.
*
* Thread safe
*/
@JsonIgnoreProperties({"base"})
public class ForeignKeySampler extends FieldSampler {
private int size = 1000;
private double skew = 0.5;
private Multinomial<Integer> base;
@SuppressWarnings("UnusedDeclaration")
public ForeignKeySampler() {
}
public ForeignKeySampler(int size, double skew) {
setSize(size);
setSkew(skew);
}
public void setSize(int size) {
Preconditions.checkArgument(size > 0);
this.size = size;
setup();
}
public void setSkew(double skew) {
Preconditions.checkArgument(skew >= 0, "Skew should be non-negative");
Preconditions.checkArgument(skew <= 3, "Skew should be less than or equal to 3");
this.skew = skew;
setup();
}
private void setup() {
base = new Multinomial<>();
for (int i = 0; i < size; i++) {
base.add(i, Math.pow(i + 1.0, -skew));
}
}
@Override
public JsonNode sample() {
synchronized (this) {
return new IntNode(base.sample());
}
}
}