…rtBasedAggregate
Normally, the aggregate operations that are invoked for an aggregation buffer for User Defined Aggregate Functions(UDAF) follow the order like initialize(), update(), eval() OR initialize(), merge(), eval(). However, after a certain threshold configurable by spark.sql.objectHashAggregate.sortBased.fallbackThreshold is reached, ObjectHashAggregate falls back to SortBasedAggregator which invokes the merge or update operation without calling initialize() on the aggregate buffer.
## What changes were proposed in this pull request?
The fix here is to initialize aggregate buffers again when fallback to SortBasedAggregate operator happens.
## How was this patch tested?
The patch was tested as part of [SPARK-24935](https://issues.apache.org/jira/browse/SPARK-24935) as documented in PR https://github.com/apache/spark/pull/23778.
Closes#24149 from pgandhi999/SPARK-27207.
Authored-by: pgandhi <pgandhi@verizonmedia.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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