Re: Difference between using a global variable and broadcasting a variable

[Fabian Hueske]

You should also be aware that the value of a static variable is only
accessible within the same JVM.
Flink is a distributed system and runs in multiple JVMs. So if you set a
value in one JVM it is not visible in another JVM (on a different node).

In general, I would avoid to use static variables in Flink programs.

Best, Fabian

2015-04-26 9:54 GMT+02:00 Sebastian <s...@apache.org>:

> Hi Hung,
>
> A broadcast variable can also refer to an intermediate result of a Flink
> computation.
>
> Best,
> Sebastian
>
>
> On 25.04.2015 21:10, HungChang wrote:
>
>> Hi,
>>
>> What would be the difference between using global variable and
>> broadcasting
>> it?
>>
>> A toy example:
>>
>> // Using global
>> {{...
>> private static int num = 10;
>> }
>>
>> public class DivByTen implements FlatMapFunction<Tuple1&lt;Double>,
>> Tuple1<Double>> {
>>    @Override
>>    public void flatMap(Tuple1<Double>value, Collector<Tuple1&lt;Double>>
>> out)
>> {
>>       out.collect(new Tuple1<Double>(value/ num));
>>    }
>> }}
>>
>> // Using broadcasting :
>> {...
>> public static class DivByTen extends
>>                         RichGMapFunction<Tuple1&lt;Double>,
>> Tuple1<Double>>{
>>
>>                 private long num;
>>
>>                 @Override
>>                 public void open(Configuration parameters) throws
>> Exception {
>>                         super.open(parameters);
>>                         num = getRuntimeContext().<Integer>
>> getBroadcastVariable(
>>                                         "num").get(0);
>>                 }
>>
>>                 @Override
>>                 public void map(Tuple1<Double>value,
>> Collector<Tuple1&lt;Double>> out))
>> throws Exception{
>>                         out.collect(new Tuple1<Double>(value/num));
>>                 }
>>         }
>> }
>>
>> Best regards,
>>
>> Hung
>>
>>
>>
>> --
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>>
>>