By default, the partition key is used for hashing then it's placed in a
partition that has the appropriate hashed keyspace.
If you have three physical partitions and then give the partition key "5"
it has nothing to do with physical partition 5 (that does not exist) ,
similar to physical: partition = hash("5") mod 3
The only guarantee is that all messages with the same key goes to the same
partition. This is useful to make sure that for example all logs from the
same ip goest to the same partition which means that they can be read by
the same producer.
/svante
2014-11-26 2:42 GMT+01:00 Haoming Zhang <haoming.zh...@outlook.com>:
>
>
>
> Hi all,
>
> I'm struggling with how to use the partition key mechanism properly. My
> logic is set the partition number as 3, then create three partition keys
> as "0", "1", "2", then use the partition keys to create three KeyedMessage
> such as
> KeyedMessage(topic, "0", message),
> KeyedMessage(topic, "1", message),
> KeyedMessage(topic, "2", message)
>
> After this, creating a producer instance to send out all the KeyedMessage.
>
> I expecting each KeyedMessage should enter to different partitions
> according to the different partition keys, which means
> KeyedMessage(topic, "0", message) go to Partition 0,
> KeyedMessage(topic, "1", message) go to Partition 1,
> KeyedMessage(topic, "2", message) go to Partition 2
>
> I'm using Kafka-web-console to watch the topic status, but the result is
> not like what I'm expecting. KeyedMessage still go to partitions randomly,
> some times two KeyedMessage will enter the same partition even they have
> different partition keys, .
>
> Not sure whether my logic is incorrect or I didn't understand the
> partition key mechanism correctly. Anyone could provides some sample code
> or explanation would be great!
>
> Thanks,
> Haoming
>
>
