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That's quite the topic. Try reading this article and tune accordingly. It might be the http threads but it also can be the processing threads in the historicals, low memory? You can read the replies to this comment and it might help you

top three generic pieces of performance advice: 1) ensure your setup is configured well for your server. we have a bunch of pre-written configs at https://druid.apache.org/docs/latest/operations/single-server.html you can start from. the most important settings to get right from the start are

druid.processing.numThreads

,

druid.processing.buffer.sizeBytes

, and

-Xmx

in jvm.config 2) ensure you don't have too many small segments: overheads per-segment can be high in this case. you can use the web console or

sys.segments

table to see the average number of rows per segment. Generally we target a few million per segment. Lower is OK if you have a smaller amount of data. But you don't want tons of segments that are, like, 10000 rows each 3) you can use a flame graph https://support.imply.io/hc/en-us/articles/360033747953-Profiling-Druid-queries-using-flame-graphs to see what specific code is taking up your processing time. very useful tool!