[GitHub] [incubator-druid] leventov commented on issue #7087: Online aggregation / Interactive Query Session Protocol

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leventov commented on issue #7087: Online aggregation / Interactive Query Session Protocol
URL: https://github.com/apache/incubator-druid/issues/7087#issuecomment-498342943
 
 
   An additional idea here (from [this paper](https://people.eecs.berkeley.edu/~brewer/Giant.pdf) by Eric Brewer, "Graceful degradation" section) is that as soon as there are first results ready for a query on a Broker, it can allow the next query to start in parallel. If the current limit of parallel queries on a Broker is X, we can make the limit of "parallel already partially computed queries" 3X or 5X, for example. This may help in case of Broker's overload so that it returns *something* useful to more clients faster (but they may wait for longer for complete results). This will also require different prioritization of per-segment queries on Historicals.
   
   The effectiveness of running some `NCPU * 5` processing threads may be reduced through unless we [move to async data processing](https://groups.google.com/d/msg/druid-development/WPfgzN3Y5i0/sgV2QoE4EQAJ) (at least in the part of the system where Broker aggregates partial results from Historicals).

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