## Problem
WAL segment fsyncs significantly affect WAL ingestion throughput.
`durable_rename()` is used when initializing every 16 MB segment, and
issues 3 fsyncs of which 1 was unnecessary.
## Summary of changes
Remove an fsync in `durable_rename` which is unnecessary with Linux and
ext4 (which we currently use). This improves WAL ingestion throughput by
up to 23% with large appends on my MacBook.
I had an impression that gc-compaction didn't test the case where the
first record of the key history is will_init because of there are some
code path that will panic in this case. Luckily it got fixed in
https://github.com/neondatabase/neon/pull/9026 so we can now implement
such tests.
Part of https://github.com/neondatabase/neon/issues/9114
## Summary of changes
* Randomly changed some images into will_init neon wal record
* Split `test_simple_bottom_most_compaction_deltas` into two test cases,
one of them has the bottom layer as delta layer with will_init flags,
while the other is the original one with image layers.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
The control file is flushed on the WAL ingest path when the commit LSN
advances by one segment, to bound the amount of recovery work in case of
a crash. This involves 3 additional fsyncs, which can have a significant
impact on WAL ingest throughput. This is to some extent mitigated by
`AppendResponse` not being emitted on segment bound flushes, since this
will prevent commit LSN advancement, which will be addressed separately.
## Summary of changes
Don't flush the control file on the WAL ingest path at all. Instead,
leave that responsibility to the timeline manager, but ask it to flush
eagerly if the control file lags the in-memory commit LSN by more than
one segment. This should not cause more than `REFRESH_INTERVAL` (300 ms)
additional latency before flushing the control file, which is
negligible.
Removes some unnecessary initdb arguments, and fixes Neon for MacOS
since it doesn't seem to ship a C.UTF-8 locale.
Signed-off-by: Tristan Partin <tristan@neon.tech>
## Problem
We wish to stop using admin tokens in the infra repo, but step down
requests use the admin token.
## Summary of Changes
Introduce a new "ControllerPeer" scope and use it for step-down requests.
Right now, our environments create databases with the C locale, which is
really unfortunate for users who have data stored in other languages
that they want to analyze. For instance, show_trgm on Hebrew text
currently doesn't work in staging or production.
I don't envision this being the final solution. I think this is just a
way to set a known value so the pageserver doesn't use its parent
environment. The final solution to me is exposing initdb parameters to
users in the console. Then they could use a different locale or encoding
if they so chose.
Signed-off-by: Tristan Partin <tristan@neon.tech>
## Problem
In test environments, the `syncfs` that the pageserver does on startup
can take a long time, as other tests running concurrently might have
many gigabytes of dirty pages.
## Summary of changes
- Add a `no_sync` option to the pageserver's config.
- Skip syncfs on startup if this is set
- A subsequent PR (https://github.com/neondatabase/neon/pull/9678) will
enable this by default in tests. We need to wait until after the next
release to avoid breaking compat tests, which would fail if we set
no_sync & use an old pageserver binary.
Q: Why is this a different mechanism than safekeeper, which as a
--no-sync CLI?
A: Because the way we manage pageservers in neon_local depends on the
pageserver.toml containing the full configuration, whereas safekeepers
have a config file which is neon-local-specific and can drive a CLI
flag.
Q: Why is the option no_sync rather than sync?
A: For boolean configs with a dangerous value, it's preferable to make
"false" the safe option, so that any downstream future config tooling
that might have a "booleans are false by default" behavior (e.g. golang
structs) is safe by default.
Q: Why only skip the syncfs, and not all fsyncs?
A: Skipping all fsyncs would require more code changes, and the most
acute problem isn't fsyncs themselves (these just slow down a running
test), it's the syncfs (which makes a pageserver startup slow as a
result of _other_ tests)
## Problem
Benchmarks need more control over the WAL generated by `WalGenerator`.
In particular, they need to vary the size of logical messages.
## Summary of changes
* Make `WalGenerator` generic over `RecordGenerator`, which constructs
WAL records.
* Add `LogicalMessageGenerator` which emits logical messages, with a
configurable payload.
* Minor tweaks and code reorganization.
There are no changes to the core logic or emitted WAL.
## Problem
https://github.com/neondatabase/neon/pull/9524 split the decoding and
interpretation step from ingestion.
The output of the first phase is a `wal_decoder::models::InterpretedWalRecord`.
Before this patch set that struct contained a list of `Value` instances.
We wish to lift the decoding and interpretation step to the safekeeper,
but it would be nice if the safekeeper gave us a batch containing the raw data instead of actual values.
## Summary of changes
Main goal here is to make `InterpretedWalRecord` hold a raw buffer which
contains pre-serialized Values.
For this we do:
1. Add a `SerializedValueBatch` type. This is `inmemory_layer::SerializedBatch` with some
extra functionality for extension, observing values for shard 0 and tests.
2. Replace `inmemory_layer::SerializedBatch` with `SerializedValueBatch`
3. Make `DatadirModification` maintain a `SerializedValueBatch`.
### `DatadirModification` changes
`DatadirModification` now maintains a `SerializedValueBatch` and extends
it as new WAL records come in (to avoid flushing to disk on every
record).
In turn, this cascaded into a number of modifications to
`DatadirModification`:
1. Replace `pending_data_pages` and `pending_zero_data_pages` with `pending_data_batch`.
2. Removal of `pending_zero_data_pages` and its cousin `on_wal_record_end`
3. Rename `pending_bytes` to `pending_metadata_bytes` since this is what it tracks now.
4. Adapting of various utility methods like `len`, `approx_pending_bytes` and `has_dirty_data_pages`.
Removal of `pending_zero_data_pages` and the optimisation associated
with it ((1) and (2)) deserves more detail.
Previously all zero data pages went through `pending_zero_data_pages`.
We wrote zero data pages when filling gaps caused by relation extension
(case A) and when handling special wal records (case B). If it happened
that the same WAL record contained a non zero write for an entry in
`pending_zero_data_pages` we skipped the zero write.
Case A: We handle this differently now. When ingesting the
`SerialiezdValueBatch` associated with one PG WAL record, we identify the gaps and fill the
them in one go. Essentially, we move from a per key process (gaps were filled after each
new key), and replace it with a per record process. Hence, the optimisation is not
required anymore.
Case B: When the handling of a special record needs to zero out a key,
it just adds that to the current batch. I inspected the code, and I
don't think the optimisation kicked in here.
## Problem
We don't have any observability for Safekeeper WAL receiver queues.
## Summary of changes
Adds a few WAL receiver metrics:
* `safekeeper_wal_receivers`: gauge of currently connected WAL
receivers.
* `safekeeper_wal_receiver_queue_depth`: histogram of queue depths per
receiver, sampled every 5 seconds.
* `safekeeper_wal_receiver_queue_depth_total`: gauge of total queued
messages across all receivers.
* `safekeeper_wal_receiver_queue_size_total`: gauge of total queued
message sizes across all receivers.
There are already metrics for ingested WAL volume: `written_wal_bytes`
counter per timeline, and `safekeeper_write_wal_bytes` per-request
histogram.
It seems the ecosystem is not so keen on moving to aws-lc-rs as it's
build setup is more complicated than ring (requiring cmake).
Eventually I expect the ecosystem should pivot to
https://github.com/ctz/graviola/tree/main/rustls-graviola as it
stabilises (it has a very simply build step and license), but for now
let's try not have a headache of juggling two crypto libs.
I also noticed that tonic will just fail with tls without a default
provider, so I added some defensive code for that.
## Problem
Decoding and ingestion are still coupled in `pageserver::WalIngest`.
## Summary of changes
A new type is added to `wal_decoder::models`, InterpretedWalRecord. This
type contains everything that the pageserver requires in order to ingest
a WAL record. The highlights are the `metadata_record` which is an
optional special record type to be handled and `blocks` which stores
key, value pairs to be persisted to storage.
This type is produced by
`wal_decoder::models::InterpretedWalRecord::from_bytes` from a raw PG
wal record.
The rest of this commit separates decoding and interpretation of the PG
WAL record from its application in `WalIngest::ingest_record`.
Related: https://github.com/neondatabase/neon/issues/9335
Epic: https://github.com/neondatabase/neon/issues/9329
## Problem
We don't have a convenient way to generate WAL records for benchmarks
and tests.
## Summary of changes
Adds a WAL generator, exposed as an iterator. It currently only
generates logical messages (noops), but will be extended to write actual
table rows later.
Some existing code for WAL generation has been replaced with this
generator, to reduce duplication.
## Problem
We wish to have high level WAL decoding logic in `wal_decoder::decoder`
module.
## Summary of Changes
For this we need the `Value` and `NeonWalRecord` types accessible there, so:
1. Move `Value` and `NeonWalRecord` to `pageserver::value` and
`pageserver::record` respectively.
2. Get rid of `pageserver::repository` (follow up from (1))
3. Move PG specific WAL record types to `postgres_ffi::walrecord`. In
theory they could live in `wal_decoder`, but it would create a circular
dependency between `wal_decoder` and `postgres_ffi`. Long term it makes
sense for those types to be PG version specific, so that will work out nicely.
4. Move higher level WAL record types (to be ingested by pageserver)
into `wal_decoder::models`
Related: https://github.com/neondatabase/neon/issues/9335
Epic: https://github.com/neondatabase/neon/issues/9329
## Problem
Part of https://github.com/neondatabase/neon/issues/8623
## Summary of changes
Removed all aux-v1 config processing code. Note that we persisted it
into the index part file, so we cannot really remove the field from
index part. I also kept the config item within the tenant config, but we
will not read it any more.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
In complement to
https://github.com/neondatabase/tokio-epoll-uring/pull/56.
## Problem
We want to make tokio-epoll-uring slots waiters queue depth observable
via Prometheus.
## Summary of changes
- Add `pageserver_tokio_epoll_uring_slots_submission_queue_depth`
metrics as a `Histogram`.
- Each thread-local tokio-epoll-uring system is given a `LocalHistogram`
to observe the metrics.
- Keep a list of `Arc<ThreadLocalMetrics>` used on-demand to flush data
to the shared histogram.
- Extend `Collector::collect` to report
`pageserver_tokio_epoll_uring_slots_submission_queue_depth`.
Signed-off-by: Yuchen Liang <yuchen@neon.tech>
Co-authored-by: Christian Schwarz <christian@neon.tech>
## Problem
`local_fs` doesn't return file sizes, which I need in PGDATA import
(#9218)
## Solution
Include file sizes in the result.
I would have liked to add a unit test, and started doing that in
* https://github.com/neondatabase/neon/pull/9510
by extending the common object storage tests
(`libs/remote_storage/tests/common/tests.rs`) to check for sizes as
well.
But it turns out that localfs is not even covered by the common object
storage tests and upon closer inspection, it seems that this area needs
more attention.
=> punt the effort into https://github.com/neondatabase/neon/pull/9510
This PR adds a pageserver mgmt API to scan a layer file for disposable
keys.
It hooks it up to the sharding compaction test, demonstrating that we're
not filtering out all disposable keys.
This is extracted from PGDATA import
(https://github.com/neondatabase/neon/pull/9218)
where I do the filtering of layer files based on `is_key_disposable`.
# Problem
Timeline creation can either be bootstrap or branch.
The distinction is made based on whether the `ancestor_*` fields are
present or not.
In the PGDATA import code
(https://github.com/neondatabase/neon/pull/9218), I add a third variant
to timeline creation.
# Solution
The above pushed me to refactor the code in Pageserver to distinguish
the different creation requests through enum variants.
There is no externally observable effect from this change.
On the implementation level, a notable change is that the acquisition of
the `TimelineCreationGuard` happens later than before. This is necessary
so that we have everything in place to construct the
`CreateTimelineIdempotency`. Notably, this moves the acquisition of the
creation guard _after_ the acquisition of the `gc_cs` lock in the case
of branching. This might appear as if we're at risk of holding `gc_cs`
longer than before this PR, but, even before this PR, we were holding
`gc_cs` until after the `wait_completion()` that makes the timeline
creation durable in S3 returns. I don't see any deadlock risk with
reversing the lock acquisition order.
As a drive-by change, I found that the `create_timeline()` function in
`neon_local` is unused, so I removed it.
# Refs
* platform context: https://github.com/neondatabase/neon/pull/9218
* product context: https://github.com/neondatabase/cloud/issues/17507
* next PR stacked atop this one:
https://github.com/neondatabase/neon/pull/9501
Persist timeline offloaded state to S3.
Right now, as of #8907, at each restart of the pageserver, all offloaded
state is lost, so we load the full timeline again. As it starts with an
empty local directory, we might potentially download some files again,
leading to downloads that are ultimately wasteful.
This patch adds support for persisting the offloaded state, allowing us
to never load offloaded timelines in the first place. The persistence
feature is facilitated via a new file in S3 that is tenant-global, which
contains a list of all offloaded timelines. It is updated each time we
offload or unoffload a timeline, and otherwise never touched.
This choice means that tenants where no offloading is happening will not
immediately get a manifest, keeping the change very minimal at the
start.
We leave generation support for future work. It is important to support
generations, as in the worst case, the manifest might be overwritten by
an older generation after a timeline has been unoffloaded (and
unarchived), so the next pageserver process instantiation might wrongly
believe that some timeline is still offloaded even though it should be
active.
Part of #9386, #8088
Add a way to list the offloaded timelines.
Before, one had to look at logs to figure out if a timeline has been
offloaded or not, or use the non-presence of a certain timeline in the
list of normal timelines. Now, one can list them directly.
Part of #8088
## Problem
Consider the following sequence of events:
1. Shard location gets downgraded to secondary while there's a libpq
connection in pagestream mode from the compute
2. There's no active tenant, so we return `QueryError::Reconnect` from
`PageServerHandler::handle_get_page_at_lsn_request`.
3. Error bubbles up to `PostgresBackendIO::process_message`, bailing us
out of pagestream mode.
4. We instruct the client to reconnnect, but continue serving the libpq
connection. The client isn't yet aware of the request to reconnect and
believes it is still in pagestream mode. Pageserver fails to deserialize
get page requests wrapped in `CopyData` since it's not in pagestream
mode.
## Summary of Changes
When we wish to instruct the client to reconnect, also disconnect from
the server side after flushing the error.
Closes https://github.com/neondatabase/cloud/issues/17336
Adds endpoint to install extensions:
**POST** `/extensions`
```
{"extension":"pg_sessions_jwt","database":"neondb","version":"1.0.0"}
```
Will be used by `local-proxy`.
Example, for the JWT authentication to work the database needs to have
the pg_session_jwt extension and also to enable JWT to work in RLS
policies.
---------
Co-authored-by: Conrad Ludgate <conradludgate@gmail.com>
This PR introduces a `/grants` endpoint which allows setting specific
`privileges` to certain `role` for a certain `schema`.
Related to #9344
Together these endpoints will be used to configure JWT extension and set
correct usage to its schema to specific roles that will need them.
---------
Co-authored-by: Conrad Ludgate <conradludgate@gmail.com>
The forever ongoing effort of juggling multiple versions of rustls :3
now with new crypto library aws-lc.
Because of dependencies, it is currently impossible to not have both
ring and aws-lc in the dep tree, therefore our only options are not
updating rustls or having both crypto backends enabled...
According to benchmarks run by the rustls maintainer, aws-lc is faster
than ring in some cases too <https://jbp.io/graviola/>, so it's not
without its upsides,
Part of the aux v1 retirement
https://github.com/neondatabase/neon/issues/8623
## Summary of changes
Remove write/read path for aux v1, but keeping the config item and the
index part field for now.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
Tenant deletion only removes the current shards from remote storage. Any
stale parent shards (before splits) will be left behind. These shards
are kept since child shards may reference data from the parent until new
image layers are generated.
## Summary of changes
* Document a special case for pageserver tenant deletion that deletes
all shards in remote storage when given an unsharded tenant ID, as well
as any unsharded tenant data.
* Pass an unsharded tenant ID to delete all remote storage under the
tenant ID prefix.
* Split out `RemoteStorage::delete_prefix()` to delete a bucket prefix,
with additional test coverage.
* Add a `delimiter` argument to `asset_prefix_empty()` to support
partial prefix matches (i.e. all shards starting with a given tenant
ID).
Adds a configuration variable for timeline offloading support. The added
pageserver-global config option controls whether the pageserver
automatically offloads timelines during compaction.
Therefore, already offloaded timelines are not affected by this, nor is
the manual testing endpoint.
This allows the rollout of timeline offloading to be driven by the
storage team.
Part of #8088
part of https://github.com/neondatabase/neon/issues/9255
## Summary of changes
Upgrade remote_storage crate to use hyper1. Hyper0 is used when
providing the streaming HTTP body to the s3 SDK, and it is refactored to
use hyper1.
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
We were seeing timeouts on migrations in this test.
The test unfortunately tends to saturate local storage, which is shared
between the pageservers and the control plane database, which makes the
test kind of unrealistic. We will also want to increase the scale of
this test, so it's worth fixing that.
## Summary of changes
- Instead of randomly creating timelines at the same time as the other
background operations, explicitly identify a subset of tenant which will
have timelines, and create them at the start. This avoids pageservers
putting a lot of load on the test node during the main body of the test.
- Adjust the tenants created to create some number of 8 shard tenants
and the rest 1 shard tenants, instead of just creating a lot of 2 shard
tenants.
- Use archival_config to exercise tenant-mutating operations, instead of
using timeline creation for this.
- Adjust reconcile_until_idle calls to avoid waiting 5 seconds between
calls, which causes timelines with large shard count tenants.
- Fix a pageserver bug where calls to archival_config during activation
get 404
## Problem
Storage controller `/control` API mostly requires admin tokens, for
interactive use by engineers. But for endpoints used by scripts, we
should not require admin tokens.
Discussion at
https://neondb.slack.com/archives/C033RQ5SPDH/p1728550081788989?thread_ts=1728548232.265019&cid=C033RQ5SPDH
## Summary of changes
- Introduce the 'infra' JWT scope, which was not previously used in the
neon repo
- For pageserver & safekeeper node registrations, require infra scope
instead of admin
Note that admin will still work, as the controller auth checks permit
admin tokens for all endpoints irrespective of what scope they require.
## Problem
We need a way to incrementally switch to direct IO. During the rollout
we might want to switch to O_DIRECT on image and delta layer read path
first before others.
## Summary of changes
- Revisited and simplified direct io config in `PageserverConf`.
- We could add a fallback mode for open, but for read there isn't a
reasonable alternative (without creating another buffered virtual file).
- Added a wrapper around `VirtualFile`, current implementation become
`VirtualFileInner`
- Use `open_v2`, `create_v2`, `open_with_options_v2` when we want to use
the IO mode specified in PS config.
- Once we onboard all IO through VirtualFile using this new API, we will
delete the old code path.
- Make io mode live configurable for benchmarking.
- Only guaranteed for files opened after the config change, so do it
before the experiment.
As an example, we are using `open_v2` with
`virtual_file::IoMode::Direct` in
https://github.com/neondatabase/neon/pull/9169
We also remove `io_buffer_alignment` config in
a04cfd754b and use it as a compile time
constant. This way we don't have to carry the alignment around or make
frequent call to retrieve this information from the static variable.
Signed-off-by: Yuchen Liang <yuchen@neon.tech>
Add /installed_extensions endpoint to collect
statistics about extension usage.
It returns a list of installed extensions in the format:
```json
{
"extensions": [
{
"extname": "extension_name",
"versions": ["1.0", "1.1"],
"n_databases": 5,
}
]
}
```
---------
Co-authored-by: Heikki Linnakangas <heikki@neon.tech>
`download_byte_range()` is basically a copy of `download()` with an
additional option passed to the backend SDKs. This can cause these code
paths to diverge, and prevents combining various options.
This patch adds `DownloadOpts::byte_(start|end)` and move byte range
handling into `download()`.
In short: Currently we reserve 75% of memory to the LFC, meaning that if
we scale up to keep postgres using less than 25% of the compute's
memory.
This means that for certain memory-heavy workloads, we end up scaling
much higher than is actually needed — in the worst case, up to 4x,
although in practice it tends not to be quite so bad.
Part of neondatabase/autoscaling#1030.
I'm trying to debug a situation with the LR benchmark publisher not
being in the correct state. This should aid in debugging, while just
being generally useful.
PR: https://github.com/neondatabase/neon/pull/9265
Signed-off-by: Tristan Partin <tristan@neon.tech>
1. Adds local-proxy to compute image and vm spec
2. Updates local-proxy config processing, writing PID to a file eagerly
3. Updates compute-ctl to understand local proxy compute spec and to
send SIGHUP to local-proxy over that pid.
closes https://github.com/neondatabase/cloud/issues/16867
## Problem
Secondary tenant heatmaps were always downloaded, even when they hadn't
changed. This can be avoided by using a conditional GET request passing
the `ETag` of the previous heatmap.
## Summary of changes
The `ETag` was already plumbed down into the heatmap downloader, and
just needed further plumbing into the remote storage backends.
* Add a `DownloadOpts` struct and pass it to
`RemoteStorage::download()`.
* Add an optional `DownloadOpts::etag` field, which uses a conditional
GET and returns `DownloadError::Unmodified` on match.
## Problem
`Oversized vectored read [...]` logs are spewing in prod because we have
a few keys that
are unexpectedly large:
* reldir/relblock - these are unbounded, so it's known technical debt
* slru block - they can be a bit bigger than 128KiB due to storage
format overhead
## Summary of changes
* Bump threshold to 130KiB
* Don't warn on oversized reldir and dbdir keys
Closes https://github.com/neondatabase/neon/issues/8967
Follow-up of #9234 to give hyper 1.0 the version-free name, and the
legacy version of hyper the one with the version number inside. As we
move away from hyper 0.14, we can remove the `hyper0` name piece by
piece.
Part of #9255
Because:
- it's nice to be up-to-date,
- we already had axum 0.7 in our dependency tree, so this avoids having
to compile two versions, and
- removes one of the remaining dpendencies to hyper version 0
Also bumps the 'tokio-tungstenite' dependency, to avoid having two
versions in the dependency tree.
* tracing-utils now returns a `Layer` impl. Removes the need for crates
to
import OTel crates.
* Drop the /v1/traces URI check. Verified that the code does the right
thing.
* Leave a TODO to hook in an error handler for OTel to log errors to
when it
assumes the regular pipeline cannot be used/is broken.
Part of https://github.com/neondatabase/cloud/issues/13127. Resolves
#9153
What changed in this PR:
1. Adds `ComputeSpec.disk_quota_bytes: Option<u64>`
2. Adds new arg to compute_ctl: `--set-disk-quota-for-fs <mountpoint>`
3. Implements running `/neonvm/bin/set-disk-quota` with the right value
if both cmdline arg AND field in the spec are specified
4. Patches `/etc/sudoers.d` to allow `compute_ctl` to set quota with
sudo
This PR is very similar to the swap support added earlier, you can take
a look at it as prior art: #7434
In theory, it can be implemented outside of compute_ctl when we will
have a separate neonvm daemon, but we are not there yet. Current
implementation is the simplest possible to unblock computes with larger
disks.
All code related to usage of `/neonvm/bin/set-disk-quota` is located in
`disk_quota.rs`. We need to call this script with the following
arguments: `/neonvm/bin/set-disk-quota {size_kb} {mountpoint}`. Quotas
are set on the filesystem level, so we need to provide path to the
directory that filesystem was mounted to.
I tested this change locally with
https://github.com/neondatabase/cloud/pull/17270. It should be safe to
merge, because this feature is gated by both cmdline arg and field in
the spec. If control-plane doesn't set values in both places,
compute_ctl won't be affected by this change.
Verbosity in this case is good when reading the code. Short options are
better when operating in an interactive shell.
Signed-off-by: Tristan Partin <tristan@neon.tech>
We separated client error from basebackup error log lines in
https://github.com/neondatabase/neon/pull/7523, but we didn't do
anything for the metrics. In this patch, we fixed it.
ref https://github.com/neondatabase/neon/issues/8970
## Summary of changes
We use the same criteria as in `log_query_error` producing an info line
(instead of error) for the metrics. We added a `client_error` category
for the basebackup query time metrics.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
Storage controller didn't previously consider AZ locality between
compute and pageservers
when scheduling nodes. Control plane has this feature, and, since we are
migrating tenants
away from it, we need feature parity to avoid perf degradations.
## Summary of changes
The change itself is fairly simple:
1. Thread az info into the scheduler
2. Add an extra member to the scheduling scores
Step (2) deserves some more discussion. Let's break it down by the shard
type being scheduled:
**Attached Shards**
We wish for attached shards of a tenant to end up in the preferred AZ of
the tenant since that
is where the compute is like to be.
The AZ member for `NodeAttachmentSchedulingScore` has been placed
below the affinity score (so it's got the second biggest weight for
picking the node). The rationale for going
below the affinity score is to avoid having all shards of a single
tenant placed on the same node in 2 node
regions, since that would mean that one tenant can drive the general
workload of an entire pageserver.
I'm not 100% sure this is the right decision, so open to discussing
hoisting the AZ up to first place.
**Secondary Shards**
We wish for secondary shards of a tenant to be scheduled in a different
AZ from the preferred one
for HA purposes.
The AZ member for `NodeSecondarySchedulingScore` has been placed first,
so nodes in different AZs
from the preferred one will always be considered first. On small
clusters, this can mean that all the secondaries
of a tenant are scheduled to the same pageserver, but secondaries don't
use up as many resources as the
attached location, so IMO the argument made for attached shards doesn't
hold.
Related: https://github.com/neondatabase/neon/issues/8848
