wuchong commented on issue #9433: [FLINK-13708] [table-planner-blink] 
transformations should be cleared after execution in blink planner
URL: https://github.com/apache/flink/pull/9433#issuecomment-523324839
 
 
   when/what/why is buffered? I will list from my understanding:
   
   1. operations should be buffered in unified table env. In order to reuse the 
shared part in the graph. And should be cleared after `execute` is invoked. 
(This is what we do currently.)
   2. transformations should be buffered in `Executor` not in 
`StreamExecutionEnvironment` in blink planner. Blink batch need to set 
additional properties on the transformation before execute. We should also 
clear the buffered transformations after `execute` is invoked.
   
   >The current state of this PR does not fix the StreamTableEnvironment with 
blink planner. You can not call execute on StreamExecutionEnvironment
   
   For `StreamTableEnvironment`, I don't think we can fix this issue. Because 
`StreamExecutionEnvironment` doesn't support `execute` multiple times. Is that 
right?
   
   > Also I don't understand why should we throw exception in explain method. 
This sounds like a rather dirty hack around some design flaws.
   
   Currently, `StreamTableEnvironment.explain` returns nothing even if we 
applied some queries before. I think throwing an exception will be better to 
warning users this method is not work properly currently. We can return the 
buffered logical/physical plan in the future, but it needs more work. 
   
   
   
   
   
   
   
   

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