pepijnve commented on PR #19287:
URL: https://github.com/apache/datafusion/pull/19287#issuecomment-3670284256

   One remaining question I have is how `skip_aggregation_probe` and 
`group_values_soft_limit` are expected to interact with the memory reservation 
system.
   
   In `SkipAggregationProbe::update_state` the total number of input rows is 
accumulated, but the only the current number of group values is compared 
against that. If disk spilling or early emission is in effect, then the 
consequence is that the ratio will only decrease since the denominator of the 
ratio keeps on increasing. In other words, it's unlikely to ever kick in.
   
   The same goes for `group_values_soft_limit`. It's compared against the 
number of group values that are held in memory by the aggregation stream 
itself. If we keep flushing values either down the pipeline or to disk, it's 
also unlikely to ever trigger.


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