The new UDF (User Defined Function) and UDA (User Defined Aggregate) introduced since Cassandra 2.2 is the feature to closest HBase co-processor.
1. They are real time, in the sense that they are applied right away on the fly after fetching data from C* 2. The computation is done on the coordinator, not on replica The second point may be surprising. One might expect that UDF and UDA computation is *distributed* among replicas but because of the eventual consistency model, data need to be retrieved and reconciled first on coordinator node (last write win) before applying any UDF or UDA. Now, if you're using consistency level ONE or LOCAL_ONE and a client with TokenAware load balancing strategy, the coordinator node is indeed the replica itself. In this particular configuration, UDF/UDA are applied locally. More info on UDF/UDA here: http://www.slideshare.net/doanduyhai/cassandra-udf-and-materialized-views On Fri, Dec 11, 2015 at 7:52 AM, Li Yang <liy...@apache.org> wrote: > This is Yang from Apache Kylin project. We are thinking about using > Cassandra instead of HBase as storage. I searched and read around and still > have one question. > > Does Cassandra support read time coprocessor that allows moving > computation to data node before scan result is returned? This shall reduce > network traffic greatly in our case. > > Thank > Yang >
