## Problem
https://github.com/neondatabase/neon/pull/8852 introduced a new nullable
column for the `nodes` table: `availability_zone_id`
## Summary of changes
* Make neon local and the test suite always provide an az id
* Make the az id field in the ps registration request mandatory
* Migrate the column to non-nullable and adjust in memory state
accordingly
* Remove the code that was used to populate the az id for pre-existing
nodes
## Problem
In order to build AZ aware scheduling, the storage controller needs to
know what AZ pageservers are in.
Related https://github.com/neondatabase/neon/issues/8848
## Summary of changes
This patch set adds a new nullable column to the `nodes` table:
`availability_zone_id`. The node registration
request is extended to include the AZ id (pageservers already have this
in their `metadata.json` file).
If the node is already registered, then we update the persistent and
in-memory state with the provided AZ.
Otherwise, we add the node with the AZ to begin with.
A couple assumptions are made here:
1. Pageserver AZ ids are stable
2. AZ ids do not change over time
Once all pageservers have a configured AZ, we can remove the optionals
in the code and make the database column not nullable.
## Problem
Previously, the controller only used the shard counts for scheduling.
This works well when hosting only many-sharded tenants, but works much
less well when hosting single-sharded tenants that have a greater
deviation in size-per-shard.
Closes: https://github.com/neondatabase/neon/issues/7798
## Summary of changes
- Instead of UtilizationScore, carry the full PageserverUtilization
through into the Scheduler.
- Use the PageserverUtilization::score() instead of shard count when
ordering nodes in scheduling.
Q: Why did test_sharding_split_smoke need updating in this PR?
A: There's an interesting side effect during shard splits: because we do
not decrement the shard count in the utilization when we de-schedule the
shards from before the split, the controller will now prefer to pick
_different_ nodes for shards compared with which ones held secondaries
before the split. We could use our knowledge of splitting to fix up the
utilizations more actively in this situation, but I'm leaning toward
leaving the code simpler, as in practical systems the impact of one
shard on the utilization of a node should be fairly low (single digit
%).
## Problem
When creating a new shard the storage controller schedules via
Scheduler::schedule_shard. This does not take into account the number of
attached shards. What it does take into account is the node affinity:
when a shard is scheduled, all its nodes (primaries and secondaries) get
their affinity incremented.
For two node clusters and shards with one secondary we have a
pathological case where all primaries are scheduled on the same node.
Now that we track the count of attached shards per node, this is trivial
to fix. Still, the "proper" fix is to use the pageserver's utilization
score.
Closes https://github.com/neondatabase/neon/issues/8041
## Summary of changes
Use attached shard count when deciding which node to schedule a fresh
shard on.
## Problem
Pageserver restarts cause read availablity downtime for tenants. See
`Motivation` section in the
[RFC](https://github.com/neondatabase/neon/pull/7704).
## Summary of changes
* Introduce a new `NodeSchedulingPolicy`: `PauseForRestart`
* Implement the first take of drain and fill algorithms
* Add a node status endpoint which can be polled to figure out when an
operation is done
The implementation follows the RFC, so it might be useful to peek at it
as you're reviewing.
Since the PR is rather chunky, I've made sure all commits build (with
warnings), so you can
review by commit if you prefer that.
RFC: https://github.com/neondatabase/neon/pull/7704
Related https://github.com/neondatabase/neon/issues/7387
## Problem
The storage controller does not track the number of shards attached to a
given pageserver. This is a requirement for various scheduling
operations (e.g. draining and filling will use this to figure out if the
cluster is balanced)
## Summary of Changes
Track the number of shards attached to each node.
Related https://github.com/neondatabase/neon/issues/7387
## Problem
- https://github.com/neondatabase/neon/issues/7355
The optimize_secondary function calls schedule_shard to check for
improvements, but if there are exactly the same number of nodes as there
are replicas of the shard, it emits some scary looking logs about no
nodes being elegible.
Closes https://github.com/neondatabase/neon/issues/7355
## Summary of changes
- Add a mode to SchedulingContext that controls logging: this should be
useful in future any time we add a log to the scheduling path, to avoid
it becoming a source of spam when the scheduler is called during
optimization.
The binary etc were renamed some time ago, but the path in the source
tree remained "attachment_service" to avoid disruption to ongoing PRs.
There aren't any big PRs out right now, so it's a good time to cut over.
- Rename `attachment_service` to `storage_controller`
- Move it to the top level for symmetry with `storage_broker` & to avoid
mixing the non-prod neon_local stuff (`control_plane/`) with the storage
controller which is a production component.
