flink-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "LINZ, Arnaud" <AL...@bouyguestelecom.fr>
Subject How to make a generic key for groupBy
Date Thu, 23 Apr 2015 14:25:10 GMT

After a quite successful benchmark yesterday (Flink being about twice faster than Spark on
my use cases), I’ve turned instantly from spark-fan to flink-fan – great job, committers!
So I’ve decided to port my existing Spark tools to Flink. Happily, most of the difficulty
was renaming classes, packages and variables with “spark” in them to something more neutral

However there is one easy thing in Spark I’m still wondering how to do in Flink : generic

I’m trying to make a framework on which my applications are built. That framework thus manipulate
“generic types” representing the data, inheriting from an abstract class with a common
contract, let’s call it “Bean”.

Among other things Bean exposes an abstract method
public Key getKey();

Key being one of my core types used in several java algorithms.

Let’s say I have the class :
public class Framework<T extends Bean> implements Serializable {

public DataSet<T> doCoolStuff(final DataSet<T> inputDataset) {
        // Group lines according to a key
        final UnsortedGrouping<YT> groupe = inputDataset.groupBy(new KeySelector<T,
Key>() {
            public Key getKey(T record)  {
                return record.getKey();

With Spark, a mapToPair works fine because all I have to do is implements correctly hashCode()
and equals() on my Key type.
With Flink, Key is not recognized as a POJO object (well it is not) and that does not work.

I have tried to expose something like public Tuple getKeyAsTuple(); in Key but Flink does
not accept generic Tuples. I’ve tried to parameterize my Tuple but Flink does not know how
to infer
the generic type value.

So I’m wondering what is the best way to implement it.
For now I have exposed something like public String getKeyAsString(); and turned my generic
treatment into :
final UnsortedGrouping<YT> groupe = inputDataset.groupBy(new KeySelector<T, String>()
            public String getKey(T record)  {
                return record.getKey().getKeyAsString();
But that “ASCII” representation is suboptimal.

I thought of passing a key to tuple conversion lambda upon creation of the Framework class
but that would be boiler-plate code on the user’s end, which I’m not fond of.

So my questions are :

-          Is there a smarter way to do this ?

-          What kind of objects can be passed as a Key ? Is there an Interface to respect

-          In the worst case, is byte[]  ok as a Key ? (I can code the serialization on the
framework side…)

Best regards,


L'intégrité de ce message n'étant pas assurée sur internet, la société expéditrice
ne peut être tenue responsable de son contenu ni de ses pièces jointes. Toute utilisation
ou diffusion non autorisée est interdite. Si vous n'êtes pas destinataire de ce message,
merci de le détruire et d'avertir l'expéditeur.

The integrity of this message cannot be guaranteed on the Internet. The company that sent
this message cannot therefore be held liable for its content nor attachments. Any unauthorized
use or dissemination is prohibited. If you are not the intended recipient of this message,
then please delete it and notify the sender.
View raw message