Files
neon/storage_controller
John Spray 715e20343a storage controller: improve scheduling of tenants created in PlacementPolicy::Secondary (#10590)
## Problem

I noticed when onboarding lots of tenants that the AZ scheduling
violation stat was climbing, before falling later as optimisations
happened. This was happening because we first add the tenant with
PlacementPolicy::Secondary, and then later go to
PlacementPolicy::Attached, and the scheduler's behavior led to a bad AZ
choice:
1. Create a secondary location in the non-preferred AZ
2. Upgrade to Attached where we promote that non-preferred-AZ location
to attached and then create another secondary
3. Optimiser later realises we're in the wrong AZ and moves us

## Summary of changes

- Extend some logging to give more information about AZs
- When scheduling secondary location in PlacementPolicy::Secondary,
select it as if we were attached: in this mode, our business goal is to
have a warm pageserver location that we can make available as attached
quickly if needed, therefore we want it to be in the preferred AZ.
- Make optimize_secondary logic the same, so that it will consider a
secondary location in the preferred AZ to be optimal when in
PlacementPolicy::Secondary
- When transitioning to from PlacementPolicy::Attached(N) to
PlacementPolicy::Secondary, instead of arbitrarily picking a location to
keep, prefer to keep the location in the preferred AZ
2025-02-03 19:01:16 +00:00
..