swy commented on FLINK-9506:

Hi [~sihuazhou] please download source from 
Could you please advice if this is the right way? It should be quite straight 
forward already in this sample test app. Please let me know if you finish 
download as I need to remove it from git. thanks.

> Flink ReducingState.add causing more than 100% performance drop
> ---------------------------------------------------------------
>                 Key: FLINK-9506
>                 URL: https://issues.apache.org/jira/browse/FLINK-9506
>             Project: Flink
>          Issue Type: Improvement
>    Affects Versions: 1.4.2
>            Reporter: swy
>            Priority: Major
>         Attachments: KeyNoHash_VS_KeyHash.png, flink.png, 
> input_stop_when_timer_run.png, keyby.png
> Hi, we found out application performance drop more than 100% when 
> ReducingState.add is used in the source code. In the test checkpoint is 
> disable. And filesystem(hdfs) as statebackend.
> It could be easyly reproduce with a simple app, without checkpoint, just 
> simply keep storing record, also with simple reduction function(in fact with 
> empty function would see the same result). Any idea would be appreciated. 
> What an unbelievable obvious issue.
> Basically the app just keep storing record into the state, and we measure how 
> many record per second in "JsonTranslator", which is shown in the graph. The 
> difference between is just 1 line, comment/un-comment "recStore.add(r)".
> {code}
> DataStream<String> stream = env.addSource(new GeneratorSource(loop);
> DataStream<JSONObject> convert = stream.map(new JsonTranslator())
>                                        .keyBy()
>                                        .process(new ProcessAggregation())
>                                        .map(new PassthruFunction());  
> public class ProcessAggregation extends ProcessFunction {
>     private ReducingState<Record> recStore;
>     public void processElement(Recordr, Context ctx, Collector<Record> out) {
>         recStore.add(r); //this line make the difference
> }
> {code}
> Record is POJO class contain 50 String private member.

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