gianm commented on issue #5006: No protections for select query
URL: 
https://github.com/apache/incubator-druid/issues/5006#issuecomment-409520315
 
 
   @RestfulBlue Have you considered the Scan query 
(http://druid.io/docs/latest/querying/scan-query.html) is meant to be a more 
memory friendly replacement for the Select query. It won't run your historicals 
out of memory. The only issue it really has is #4933, and that's a broker 
thing, not historicals. And it only can happen with very large or unlimited 
scan limits.
   
   You could also consider adding a property for maxResults to 
SelectQueryConfig, and having that be a cap on the number of results that a 
Select query is allowed to return. With the way Select is written, though, it 
might be challenging to implement. Select's real problem is that it selects 
threshold-number of rows per each segment in parallel and then limits them 
later. This causes it to use up a lot more memory than you expect, and can also 
make it tough to implement a maxResults limit.

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