Describe the problem

I ran across an interesting observation while trying to explain how queries are run in parallel within CRDB. I was using the internal KV workload and have a fair number of ranges distributed across three nodes:

root@:26257/kv> SELECT k2, count(*) FROM kv GROUP BY k2;
    k2   |  count
---------+----------
  z      | 4561620
  needle |       8
  

I was expecting that the above query would run in parallel, but when looking at the Jaeger trace collected, it appears to not be serial.

At the advise of engineering, I ran this by disabling vectorization SET vectorize = off and it appeared to run as expected albeit longer.