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-525681413
 
 
   Hi @dawidwys , 
   
   After revisiting the code of `StreamExecutionEnvironment`, I find that I'm 
wrong. `StreamExecutionEnvironment` supports to execute multiple times, because 
it will clear the buffered transformations.
   
   Regarding to why we need execute multiple times:
   1) we didn't forbid to execute multiple times in the JavaDoc of `execute` 
method.
   2) `StreamExecutionEnvironment` also supports execute multiple times. 
   3)  We are doing the benchmark for TPC-DS queries and the total time is one 
of the important metrics. Meanwhile, we will collect and register some 
statistics in the built-in catalog, this will takes some time because it will 
spawn some jobs to calculate ndv, row-count, etc... If the TableEnvironment 
doesn't support execute multiple times, we have to re-calculate the statistics 
and re-construct TableEnvironment, this will prolong the total benchmark time. 
   
   
   
   
   
   

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