Deprecate and remove "Cancel Prebuilds on Outdated Commits" feature

[jankeromnes]

Is your feature request related to a problem? Please describe

In an effort to optimize Prebuilds, we've previously introduced a Project Settings feature called "Cancel Prebuilds on Outdated Commits":

What this feature does is: When new commits are pushed to a given branch, automatically cancel any prebuilds that are currently still running for this branch.

Unfortunately, this feature doesn't quite work as we intended, and it has a number of unfortunate side effects:

• For projects with a low commit frequency, this feature does nothing (i.e. prebuilds are always finished before the next push, so this feature brings zero value)

• For projects with a high commit frequency, this feature:

  • Wastes a lot of compute time (i.e. many prebuilds are triggered, then they run for a while, then they are often discarded when the next push arrives)
  • Rarely produces any actually-usable prebuild (in a busy day, many prebuilds are run and discarded, but the very first prebuild that manages to run until completion happens only when the commit frequency goes down again, e.g. during a lunch break or at the end of a work day when most committers are co-located)
  • Does not actually "cancel" prebuilds semantically, but produces many "System Errors" instead: https://github.com/gitpod-io/gitpod/issues/13874

Describe the behaviour you'd like

We should deprecate and remove the "Cancel Prebuilds on Outdated Commits" feature, because it doesn't work well.

Describe alternatives you've considered

We already have better alternatives to optimize prebuilds:

https://github.com/gitpod-io/gitpod/blob/08be4195d40cbea9248847547a8fc25fe44f3cba/components/server/ee/src/prebuilds/prebuild-manager.ts#L243-L258

Additional context

[easyCZ]

Should also deprecate (not remove) it from https://github.com/gitpod-io/gitpod/blob/main/components/public-api/gitpod/experimental/v1/projects.proto#L51 used by the public api

[svenefftinge]

For projects with a low commit frequency, this feature does nothing (i.e. prebuilds are always finished before the next push, so this feature brings zero value)

A very common working mode is to force push on a branch. In those case any running prebuilds should always be immediately cancelled (no opt-out), because they are no longer reachable (the commit doesn't exist).

The original motivation for this feature was to cancel prebuilds that are non-reachable. I.e. where the commit no longer exists (force-pushed) or has been superseded by a new commit. The latter are now reachable since we use older prebuilds and incrementally update them. So we can deprecate that part but killing prebuilds for which no commit exists would still make sense.

[stale[bot]]

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