Production 1-query timing estimator (R&D phase)

Goal

As a user of DLE and/or Joe bot, I want to see a timing estimate for production.

Why: Depending on configuration, resources, and state of caches, DLE can execute queries significantly longer than production Postgres.

TODO / How to implement

• we need to provide 2 numbers always, for cold and hot cache state. (Display as a range: Production timing estimate: XX-YY ms)
• exec (DDL): count buffers read and written (either using /proc/... or pg_stat_database), and based on those numbers and knowledge about prod, provide ...
• explain: ...
• how do we "learn" how production behaves? (calibration)
• should we provide "error" in addition to estimate?

Acceptance criteria

• Joe users see production timing estimate for both explain and exec. Questions to finalize:

• UI: wording, put it into the summary
• Are we going to show wait_even_type histogram right now? For every Joe's response?
• (implementation) which event types do we need to involve in the formula?
• DOCUMENTATION docs#42 (closed)
• link to "how it works" (users should be able to find it easily: look at Summary -> think "how" -> go read the doc)

• DLE users – ??? (option: CI observer also provides estimates for ???)