adriangb commented on PR #21182:
URL: https://github.com/apache/datafusion/pull/21182#issuecomment-4190429069

   > 8MB was too small for wide-row full scans (Q3: SELECT * with 16 columns),
   causing SPM to stall on I/O. 64MB per partition is still strictly less
   than the SortExec it replaces (which buffers entire partition in memory).
   BufferExec integrates with MemoryPool so it won't cause OOM.
   
   I think this is right. Basically: `SortExec` is "unlimited" buffering. IMO 
we could go even higher if we have to a pick a number (although perhaps it 
should be configurable if it isn't already) - something like 512MB. If the 
partition is smaller it will never be hit. If it is larger or we run out of 
memory it will spill.
   
   But let's see what the numbers look like with 64MB.


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