2010YOUY01 commented on issue #19846:
URL: https://github.com/apache/datafusion/issues/19846#issuecomment-3758770974

   +1 for option 2, here are the reasons:
   
   This does affect functional correctness. For example, if a batch is 10 MB 
before spilling, after spilling and reading it back it may become 12 MB. The 
external sorter's merge phase then reserves memory based on the original 10 MB 
estimate, while the actual memory usage exceeds the memory pool’s expectation.
   
   Since DataFusion’s memory pool already allows a certain margin of error 
between estimated and actual memory usage, I think Option 2 is a good idea. We 
can tolerate, for example, a 20% estimation error, but order-of-magnitude 
errors (e.g., 10×) should still be treated as bugs, warned about, and fixed.


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