sunchao commented on PR #4819:
URL: https://github.com/apache/arrow-rs/pull/4819#issuecomment-1721499590

   > I recall you mentioning the dictionary encoding overheads were very high 
in your workloads
   
   Thanks @tustvold ! Yes, we observed the columnar-to-row conversion for 
dictionary encoding incurs quite some overhead. Even in my current vectorized 
hash table POC, which is based of 
[`GroupValuesRows`](https://github.com/apache/arrow-datafusion/blob/main/datafusion/core/src/physical_plan/aggregates/group_values/row.rs#L89),
 the conversion takes about 30% of total hash table time, measured from running 
`tpch_mem` and `clickbench_1`.


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