David Anderson created FLINK-8914:
-------------------------------------
Summary: CEP's greedy() modifier doesn't work
Key: FLINK-8914
URL: https://issues.apache.org/jira/browse/FLINK-8914
Project: Flink
Issue Type: Bug
Components: CEP
Affects Versions: 1.4.1, 1.4.0
Reporter: David Anderson
When applied to the first or last component of a CEP Pattern, greedy() doesn't
work correctly. Here's an example:
{code:java}
package com.dataartisans.flinktraining.exercises.datastream_java.cep;
import org.apache.flink.cep.CEP;
import org.apache.flink.cep.PatternSelectFunction;
import org.apache.flink.cep.PatternStream;
import org.apache.flink.cep.pattern.Pattern;
import org.apache.flink.cep.pattern.conditions.SimpleCondition;
import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import java.util.List;
import java.util.Map;
public class RunLength {
public static void main(String[] args) throws Exception {
StreamExecutionEnvironment env =
StreamExecutionEnvironment.getExecutionEnvironment();
env.setParallelism(1);
DataStream<Integer> input = env.fromElements(1, 1, 1, 1, 1, 0, 1, 1, 1, 0);
Pattern<Integer, ?> onesThenZero = Pattern.<Integer>begin("ones")
.where(new SimpleCondition<Integer>() {
@Override
public boolean filter(Integer value) throws Exception {
return value == 1;
}
})
.oneOrMore()
.greedy()
.consecutive()
.next("zero")
.where(new SimpleCondition<Integer>() {
@Override
public boolean filter(Integer value) throws Exception {
return value == 0;
}
});
PatternStream<Integer> patternStream = CEP.pattern(input, onesThenZero);
// Expected: 5 3
// Actual: 5 4 3 2 1 3 2 1
patternStream.select(new LengthOfRun()).print();
env.execute();
}
public static class LengthOfRun implements PatternSelectFunction<Integer,
Integer> {
public Integer select(Map<String, List<Integer>> pattern) {
return pattern.get("ones").size();
}
}
}
{code}
The only workaround for now seems to be to rewrite the pattern so that greedy()
isn't needed – i.e. by bracketing the greedy section with a prefix and suffix
that both have to be matched.
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