#4430 introduced two new settings:

• max_execution_speed
• max_execution_speed_bytes

Both of which should be very useful in a multi tenant environment, especially as a poor's man non-conserving query prioritization.

When progressImpl is called it checks current execution speed and if it higher than set in settings it sleeps, thus introducing back-pressure to executing threads. (?)

It doesn't seem to work when running aggregations (SELECT count()...) over a cluster (a distributed table). These limits are checked only on the executor node on a progress packet arrival, even though the thread that checked the limit sleeps, the back-pressure is not propagated to leaf nodes as these have no data to push to executor until the whole query is finished.

cc @zhang2014