Cheng Lian reassigned SPARK-17949:

    Assignee: Cheng Lian

> Introduce a JVM object based aggregate operator
> -----------------------------------------------
>                 Key: SPARK-17949
>                 URL: https://issues.apache.org/jira/browse/SPARK-17949
>             Project: Spark
>          Issue Type: Improvement
>          Components: SQL
>            Reporter: Reynold Xin
>            Assignee: Cheng Lian
> The new Tungsten execution engine has very robust memory management and speed 
> for simple data types. It does, however, suffer from the following:
> 1. For user defined aggregates (Hive UDAFs, Dataset typed operators), it is 
> fairly expensive to fit into the Tungsten internal format.
> 2. For aggregate functions that require complex intermediate data structures, 
> Unsafe (on raw bytes) is not a good programming abstraction due to the lack 
> of structs.
> The idea here is to introduce an JVM object based hash aggregate operator 
> that can support the aforementioned use cases. This operator, however, should 
> limit its memory usage to avoid putting too much pressure on GC, e.g. falling 
> back to sort-based aggregate as soon the number of objects exceed a very low 
> threshold.
> Internally at Databricks we prototyped a version of this for a customer POC 
> and have observed substantial speed-ups over existing Spark.

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