kaisun2000 commented on issue #12721:
URL: https://github.com/apache/druid/issues/12721#issuecomment-1984935814

   Copy the [slack channel 
comment](https://apachedruidworkspace.slack.com/archives/C030CMF6B70/p1709862138570539?thread_ts=1704511189.243569&cid=C030CMF6B70)
 here:
   
   For the past two month, I worked on some query performance tuning in our 
system, mainly to reduce the query latency and specifically in the real time 
path. In the mean time, I find that a query insight tool like proposed above 
would be very valuable.
   More specifically, the following would be useful and some of them are 
missing:
   1/ per segment query processing time
   2/ per segment waiting time for the processing queue and current queue size
   3/ per hydrant query processing time -- missing
   4/ per hydrant waiting time thread time -- if paralleled, missing
   5/ per query merge buffer acquisition time and current waiting queue size -- 
missing
   6/ post segment processing grouper potentially spilling to disk time -- 
missing
   These information should not be limited to only brokers, but also data node 
(peons and historicals).
   
   The main idea is
   attribute time spent for each query in each stage and report contention 
points statistics such as the thread pool queue length while waiting, or merge 
buffer queue length while waiting, or spilling to disk activity for groupers.
   report this data collectively to some UI so that admin can have a direct 
insights above queries and why they may be slow.


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