[GitHub] pgandhi999 edited a comment on issue #23778: [SPARK-24935][SQL] : Problem with Executing Hive UDF's from Spark 2.2 Onwards

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pgandhi999 edited a comment on issue #23778: [SPARK-24935][SQL] : Problem with Executing Hive UDF's from Spark 2.2 Onwards
URL: https://github.com/apache/spark/pull/23778#issuecomment-466176136
 
 
   Sure @cloud-fan . Thank you for your response. As far as my understanding of Hive UDAF is concerned, I can roughly classify them into into types: those that support partial aggregation(Mode PARTIAL and FINAL) and those that do not(Mode COMPLETE). For the Hive UDAFs that support partial aggregation, there are five phases:
   - **Initialize:** The aggregation buffers for PARTIAL1 Mode and PARTIAL2 Mode are created in this phase.
   - **Iterate(Update) :** This state processes a new row of data into the aggregation buffer created for PARTIAL1.
   - **TerminatePartial:** Returns the contents of the aggregation buffer.
   - **Merge:** Merges a partial aggregation returned by calling terminatePartial() on PARTIAL1 aggregation buffer into the current aggregation happening on PARTIAL2 aggregation buffer.
   - **Terminate:** Returns the final result of the aggregation stored in PARTIAL2 buffer to Hive.  
   
   For the Hive UDAFs that do not support partial aggregation, I have seen the following three phases:
   -**Initialize:** Initialize the aggregation buffer.
   -**Iterate(Update):** Process the rows into the buffer.
   -**Terminate:** Return the final result.
   
   For more information, you may find this link helpful: https://cwiki.apache.org/confluence/display/Hive/GenericUDAFCaseStudy
   
   This information is based on what I have found out during my tests and reading through the docs and it is based on this information that I have modeled the behaviour of the class `HiveTypedImperativeAggregate`. I am by no means an expert on Hive, so if you feel that my summary on Hive UDAFs is incorrect or is missing something, please let me know. 

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