imay commented on issue #831: Powerful Improve: parallel scan exec instance
URL: https://github.com/apache/incubator-doris/issues/831#issuecomment-477607940
 
 
   @kangkaisen 
   
   Wonderful job!!!
   
   It is very useful for single query's performance. However this is bad for 
broadcast join, because inner table will be sent more times, and more memory 
would be taken. So  I think adding a new config to limit max instances is 
acceptable. 
   
   And now Doris's query optimizer can't decide when to use broadcast join or 
shuffle join, we should improve our optimizer. And our optimizer should decide 
how many scan instances should be allocated according to its data size. Then we 
can drop this config item. 
   
   Looking forward to your PR

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