baiguoname commented on issue #18202:
URL: https://github.com/apache/datafusion/issues/18202#issuecomment-3454782091

   > I see, I cannot see any blocking operator in the final plan. The problem 
might be related to the CoalesceBatchesExec, whose target_batch_size=8192. 
Waiting for 8192 rows for each partition may take a while, if you set the 
configuration: "datafusion.execution.batch_size" to a smaller value (such as 1) 
you might see results even in the multi partition case. Other than this I 
cannot think any reason why you don't see any result when query runs in multi 
partitions.
   
   Another question: could you briefly describe how to determine if an operator 
is blocking or not? I found no documentation on this topic and have to 
repeatedly test it by examining the information from the `SanityCheckPlan` 
optimizer.


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