HeartSaVioR commented on pull request #31522:
URL: https://github.com/apache/spark/pull/31522#issuecomment-794426247


   I think the key arguments here are "how much time the committing can take at 
worse case" and "how frequently it occurs".
   
   I have no answer for second one as I could only hear from the customers' 
when they complained, but I can give the first one according to customers' 
case. That's not just 10s of seconds of course. (I would rather say they only 
concern when the gap is "significant", not just a few more mins.) It can be 
couple of hours or even longer on HDFS unhealthy case. Most likely their 
complaints on this behavior are "why the Spark driver got hang?", because 
there's no log during committing, unless they turned on DEBUG log for Hadoop 
code path.
   
   That said, I have mixed feeling on this. I agree that explaining the missing 
time range is important when we track back the problem from event log, but 
assume the commit ended somehow, then the log will tell. I would like to know 
about the answer of second one in production before making decision, but if the 
case is not happening often, that might be something we can live with.
   
   And for the extreme case like taking hours on committing, I think more 
important thing is to log periodically to let end users determine whether the 
Spark driver is hang or not, without enabling DEBUG log for sure. Maybe 
off-topic, but if we'd like to have priority on these things, I'd rather say 
that's more needed.


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