Ability to reject queries via routing rules

[vaultah]

It'd be helpful to be able to reject incoming queries completely.

For example, if we had an empty terminal routing group, we could have a routing rule file similar to

...
---
name: "Bad queries handling"
description: >
  Reject bad queries before they reach Trino clusters
priority: 100000
condition: >
  isBadQuery(trinoQueryProperties)
actions:
  - "result.put('routingGroup', 'deny')"

This is currently not possible because trino-gateway always attempts to route queries to adhoc as the last resort.

[xkrogen]

+1 on this feature. We actually sometimes do this in emergency scenarios by adding a new cluster with an endpoint that doesn't exist, and routing the query there, but it's certainly not ideal! Having a way to properly express this in the routing layer would be great.

[Chaho12]

You can do this by simply creating a custom routing manager and override methods.

[mosabua]

Agreed @Chaho12 but I think it would make sense to have this sort of functionality as a routing manager that we ship as part of the project or even a core functionality. I believe the work @vishalya is doing will actually lead to that.