GroupBy/TopN Queries Not Honoring druid.processing.buffer.sizeBytes


I am run into a weird issue wherein I have set proessing buffer size to 1 bytes in the config on the broker.

Now as per the documentation on Druid , The meaning of that field is “This specifies a buffer size for the storage of intermediate results. The computation engine in both the Historical and Realtime nodes will use a scratch buffer of this size to do all of their intermediate computations off-heap. Larger values allow for more aggregations in a single pass over the data while smaller values can require more passes depending on the query that is being executed.”

I ran typical TopN and GroupBy Queries but there seems to be no error and everything seems to be working.

Query Time also does not seems to be affected by this, atleast for TopN query.

So what is the use of these processing buffer and merging result buffers ?

I have kept the size to 1 byte and nothing seems to be crashing or working.

Please help.


Pravesh Gupta