Dandandan commented on pull request #706:
URL: https://github.com/apache/arrow-datafusion/pull/706#issuecomment-877844585


   > > One concern I have is that the current config also sets the number of 
maximum threads during reading parquet files.
   > 
   > Is this still true though? I know we were creating threads at one point in 
time but we are using Tokio/async now, so we are not creating threads. 
Increasing partition count will increase the number of async tasks that we run 
in the thread pool but won't increase the number of threads.
   
   We run the tasks now with `spawn_blocking`, this will still create a number 
of extra threads to execute the task on. This is set to create a maximum of 
512(!) threads by default. Based on the `max_concurrency` we still split the 
files into multiple parallel readers, so increasing this value will increase 
the number of extra threads (and allocated data) we use considerably as far as 
I can see.


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