Jay Kreps created KAFKA-925:
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Summary: Add optional partition key override in producer
Key: KAFKA-925
URL: https://issues.apache.org/jira/browse/KAFKA-925
Project: Kafka
Issue Type: New Feature
Components: producer
Affects Versions: 0.8.1
Reporter: Jay Kreps
Assignee: Jay Kreps
We have a key that is used for partitioning in the producer and stored with the
message. Actually these uses, though often the same, could be different. The
two meanings are effectively:
1. Assignment to a partition
2. Deduplication within a partition
In cases where we want to allow the client to take advantage of both of these
and they aren't the same it would be nice to allow them to be specified
separately.
To implement this I added an optional partition key to KeyedMessage. When
specified this key is used for partitioning rather than the message key. This
key is of type Any and the parametric typing is removed from the partitioner to
allow it to work with either key.
An alternative would be to allow the partition id to specified in the
KeyedMessage. This would be slightly more convenient in the case where there is
no partition key but instead you know a priori the partition number--this case
must be handled by giving the partition id as the partition key and using an
identity partitioner which is slightly more roundabout. However this is
inconsistent with the normal partitioning which requires a key in the case
where the partition is determined by a key--in that case you would be manually
calling your partitioner in user code. It seems best to me to either use a key
or always a partition and since we currently take a key I stuck with that.
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