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`.
Before, we didn't copy over the `index-part.json` of offloaded timelines
to the new shard's location, resulting in the new shard not knowing the
timeline even exists.
In #9444, we copy over the manifest, but we also need to do this for
`index-part.json`.
As the operations to do are mostly the same between offloaded and
non-offloaded timelines, we can iterate over all of them in the same
loop, after the introduction of a `TimelineOrOffloadedArcRef` type to
generalize over the two cases. This is analogous to the deletion code
added in #8907.
The added test also ensures that the sharded archival config endpoint
works, something that has not yet been ensured by tests.
Part of #8088
## Problem
https://github.com/neondatabase/neon/pull/9492 added a metric to track
the total count of block gaps filled on rel extend. More context is
needed to understand when this happens. The current theory is that it
may only happen on pg 14 and pg 15 since they do not WAL log relation extends.
## Summary of Changes
A rate limited log is added.
# 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
## Problem
WAL ingest couples decoding of special records with their handling
(updates to the storage engine mostly).
This is a roadblock for our plan to move WAL filtering (and implicitly
decoding) to safekeepers since they cannot
do writes to the storage engine.
## Summary of changes
This PR decouples the decoding of the special WAL records from their
application. The changes are done in place
and I've done my best to refrain from refactorings and attempted to
preserve the original code as much as possible.
Related: https://github.com/neondatabase/neon/issues/9335
Epic: https://github.com/neondatabase/neon/issues/9329
part of https://github.com/neondatabase/neon/issues/9114,
https://github.com/neondatabase/neon/issues/8836,
https://github.com/neondatabase/neon/issues/8362
The split layer writer code can be used in a more general way: the
caller puts unfinished writers into the batch layer writer and let batch
layer writer to ensure the atomicity of the layer produces.
## Summary of changes
* Add batch layer writer, which atomically finishes the layers.
`BatchLayerWriter::finish` is simply a copy-paste from previous split
layer writers.
* Refactor split writers to use the batch layer writer.
* The current split writer tests cover all code path of batch layer
writer.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
Filling the gap in with zeroes is annoying for sharded ingest. We are
not sure it even happens in reality.
## Summary of Changes
Add one global counter which tracks how many such gap blocks we filled
on relation extends. We can add more metrics once we understand the
scope.
similar to https://github.com/neondatabase/neon/pull/8841, we make the
delta layer writer atomic when finishing the layers.
## Summary of changes
* `put_value` not taking discard fn anymore
* `finish` decides what layers to keep
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
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
Part of #8130
## Problem
Pageserver previously goes through the kernel page cache for all the
IOs. The kernel page cache makes light-loaded pageserver have deceptive
fast performance. Using direct IO would offer predictable latencies of
our virtual file IO operations.
In particular for reads, the data pages also have an extremely low
temporal locality because the most frequently accessed pages are cached
on the compute side.
## Summary of changes
This PR enables pageserver to use direct IO for delta layer and image
layer reads. We can ship them separately because these layers are
write-once, read-many, so we will not be mixing buffered IO with direct
IO.
- implement `IoBufferMut`, an buffer type with aligned allocation
(currently set to 512).
- use `IoBufferMut` at all places we are doing reads on image + delta
layers.
- leverage Rust type system and use `IoBufAlignedMut` marker trait to
guarantee that the input buffers for the IO operations are aligned.
- page cache allocation is also made aligned.
_* in-memory layer reads and the write path will be shipped separately._
## Testing
Integration test suite run with O_DIRECT enabled:
https://github.com/neondatabase/neon/pull/9350
## Performance
We evaluated performance based on the `get-page-at-latest-lsn`
benchmark. The results demonstrate a decrease in the number of IOps, no
sigificant change in the latency mean, and an slight improvement on the
p99.9 and p99.99 latencies.
[Benchmark](https://www.notion.so/neondatabase/Benchmark-O_DIRECT-for-image-and-delta-layers-2024-10-01-112f189e00478092a195ea5a0137e706?pvs=4)
## Rollout
We will add `virtual_file_io_mode=direct` region by region to enable
direct IO on image + delta layers.
Signed-off-by: Yuchen Liang <yuchen@neon.tech>
Part of https://github.com/neondatabase/neon/issues/8836
## Summary of changes
This pull request makes the image layer split writer atomic when
finishing the layers. All the produced layers either finish at the same
time, or discard at the same time. Note that this does not prevent
atomicity when crash, but anyways, it will be cleaned up on pageserver
restart.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
Co-authored-by: Christian Schwarz <christian@neon.tech>
In #9453, we want to remove the non-gzipped basebackup code in the
computes, and always request gzipped basebackups.
However, right now the pageserver's page service only accepts basebackup
requests in the following formats:
* `basebackup <tenant_id> <timeline_id>`, lsn is determined by the
pageserver as the most recent one (`timeline.get_last_record_rlsn()`)
* `basebackup <tenant_id> <timeline_id> <lsn>`
* `basebackup <tenant_id> <timeline_id> <lsn> --gzip`
We add a fourth case, `basebackup <tenant_id> <timeline_id> --gzip` to
allow gzipping the request for the latest lsn as well.
## Problem
The pageserver generally trusts the storage controller/control plane to
give it valid generations. However, sometimes it should be obvious that
a generation is bad, and for defense in depth we should detect that on
the pageserver.
This PR is part 1 of 2:
1. in this PR we detect and warn on such situations, but do not block
starting up the tenant. Once we have confidence that the check is not
firing unexpectedly in the field
2. part 2 of 2 will introduce a condition that refuses to start a tenant
in this situtation, and a test for that (maybe, if we can figure out how
to spoof an ancient mtime)
Related: #6951
## Summary of changes
- When loading an index older than 2 weeks, log an INFO message noting
that we will check for other indices
- When loading an index older than 2 weeks _and_ a newer-generation
index exists, log a warning.
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).
part of https://github.com/neondatabase/neon/issues/9114
## Summary of changes
gc-compaction may take a lot of disk space, and if it does, the caller
should do a partial gc-compaction. This patch adds space check for the
compaction job.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
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
The current code has forgotten to activate timelines during unoffload,
leading to inability to receive the basebackup, due to the timeline
still being in loading state.
```
stderr:
command failed: compute startup failed: failed to get basebackup@0/0 from pageserver postgresql://no_user@localhost:15014
Caused by:
0: db error: ERROR: Not found: Timeline 508546c79b2b16a84ab609fdf966e0d3/bfc18c24c4b837ecae5dbb5216c80fce is not active, state: Loading
1: ERROR: Not found: Timeline 508546c79b2b16a84ab609fdf966e0d3/bfc18c24c4b837ecae5dbb5216c80fce is not active, state: Loading
```
Therefore, also activate the timeline during unoffloading.
Part of #8088
## Problem
In test `test_timeline_offloading`, we see failures like:
```
PageserverApiException: queue is in state Stopped
```
Example failure:
https://neon-github-public-dev.s3.amazonaws.com/reports/main/11356917668/index.html#testresult/ff0e348a78a974ee/retries
## Summary of changes
- Amend code paths that handle errors from RemoteTimelineClient to check
for cancellation and emit the Cancelled error variant in these cases
(will give clients a 503 to retry)
- Remove the implicit `#[from]` for the Other error case, to make it
harder to add code that accidentally squashes errors into this
(500-equivalent) error variant.
This would be neater if we made RemoteTimelineClient return a structured
error instead of anyhow::Error, but that's a bigger refactor.
I'm not sure if the test really intends to hit this path, but the error
handling fix makes sense either way.
Our replication bench project is stuck because it is too slow to
generate basebackup and it caused compute to disconnect.
https://neondb.slack.com/archives/C03438W3FLZ/p1728330685012419
The compute timeout for waiting for basebackup is 10m (is it true?).
Generating basebackup directly on pageserver takes ~3min. Therefore, I
suspect it's because there are too many wasted round-trip time for
writing the 10000+ snapshot aux files. Also, it is possible that the
basebackup process takes too long time retrieving all aux files that it
did not write anything over the wire protocol, causing a read timeout.
Basebackup size is 800KB gzipped for that project and was 55MB tar
before compression.
## Summary of changes
* Potentially fix the issue by placing a write buffer for basebackup.
* Log how many aux files did we read + the time spent on it.
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
There is double update of resize cache in `put_rel_truncation`
Also `page_server_request` contains check that fork is MAIN_FORKNUM
which
1. is incorrect (because Vm/FSM pages are shreded in the same way as
MAIN fork pages and
2. is redundant because `page_server_request` is never called for `get
page` request so first part to OR condition is always true.
## Summary of changes
Remove redundant code
## Checklist before requesting a review
- [ ] I have performed a self-review of my code.
- [ ] If it is a core feature, I have added thorough tests.
- [ ] Do we need to implement analytics? if so did you add the relevant
metrics to the dashboard?
- [ ] If this PR requires public announcement, mark it with
/release-notes label and add several sentences in this section.
## Checklist before merging
- [ ] Do not forget to reformat commit message to not include the above
checklist
---------
Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>
Add a test for timeline offloading, and subsequent unoffloading.
Also adds a manual endpoint, and issues a proper timeline shutdown
during offloading which prevents a pageserver hang at shutdown.
Part of #8088.
## 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
Also consider offloaded timelines for obtaining `retain_lsn`. This is
required for correctness for all timelines that have not been flattened
yet: otherwise we GC data that might still be required for reading.
This somewhat counteracts the original purpose of timeline offloading of
not having to iterate over offloaded timelines, but sadly it's required.
In the future, we can improve the way the offloaded timelines are
stored.
We also make the `retain_lsn` optional so that in the future, when we
implement flattening, we can make it None. This also applies to full
timeline objects by the way, where it would probably make most sense to
add a bool flag whether the timeline is successfully flattened, and if
it is, one can exclude it from `retain_lsn` as well.
Also, track whether a timeline was offloaded or not in `retain_lsn` so
that the `retain_lsn` can be excluded from visibility and size
calculation.
Part of #8088
## 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>
`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()`.
Implements an initial mechanism for offloading of archived timelines.
Offloading is implemented as specified in the RFC.
For now, there is no persistence, so a restart of the pageserver will
retrigger downloads until the timeline is offloaded again.
We trigger offloading in the compaction loop because we need the signal
for whether compaction is done and everything has been uploaded or not.
Part of #8088
## 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
As seen in https://github.com/neondatabase/cloud/issues/17335, during
releases we can have ingest lags that are above the limits for warnings.
However, such lags are part of normal pageserver startup.
Therefore, calculate a certain cooldown timestamp until which we accept
lags up to a certain size. The heuristic is chosen to grow the later we get
to fully load the tenant, and we also add 60 seconds as a grace period
after that term.
close https://github.com/neondatabase/neon/issues/9160
For whatever reason, pg17's WAL pattern seems different from others,
which triggers some flaky behavior within the compaction smoke test.
## Summary of changes
* Run L0 compaction before proceeding with the read benchmark.
* So that we can ensure the num of L0 layers is 0 and test the
compaction behavior only with L1 layers.
We have a threshold for triggering L0 compaction. In some cases, the
test case did not produce enough L0 layers to do a L0 compaction,
therefore leaving the layer map with 3+ L0 layers above the L1 layers.
This increases the average read depth for the timeline.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
Recent change to avoid the "became visible" log messages from certain
tasks missed a task: the logical size calculation that happens as a
child of synthetic size calculation.
Related: https://github.com/neondatabase/neon/issues/9058
## Summary of changes
- Add OnDemandLogicalSize to the list of permitted tasks for reads
making a covered layer visible
- Tweak the log message to use layer name instead of key: this is more
terse, and easier to use when debugging, as one can search for it
elsewhere to see when the layer was written/downloaded etc.
Following #7656, `TenantConfOpt::TryFrom<toml_edit::Item>` appears to be
dead code. This patch removes `TenantConfOpt::TryFrom<toml_edit::Item>`.
The code does appear to be dead, since the TOML config is deserialized
into `TenantConfig` (via `LocationConfig`) and then converted into
`TenantConfOpt`.
This was verified by adding a panic to `try_from()` and running the
pageserver unit tests as well as a local end-to-end cluster (including
creating a new tenant and restarting the pageserver). This did not fail,
so this is not used on the common happy path at least. No explicit
`try_from` or `try_into` calls were found either.
Resolves#8918.
## Problem
Legacy functions that were called as `mgr::` and relied on the static
TENANTS, see #5796
## Summary of changes
- Move the last stray function (immediate_gc) into TenantManager
Closes: https://github.com/neondatabase/neon/issues/5796
close https://github.com/neondatabase/neon/issues/8140
The original issue is rather vague on what we should do. After
discussion w/ @problame we decided to narrow down the problems we want
to solve in that issue.
* read path -- do not panic for now.
* write path -- panic only on write errors (i.e., device error, fsync
error), but not on no-space for now.
The guideline is that if the pageserver behavior could lead to violation
of persistent constraints (i.e., return an operation as successful but
not actually persisting things), we should panic. Fsync is the place
where both of us agree that we should panic, because if fsync fails, the
kernel will mark dirty pages as clean, and the next fsync will not
necessarily return false. This would make the storage client assume the
operation is successful.
## Summary of changes
Make fsync panic on fatal errors.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
Part of #8130
## Problem
After deploying https://github.com/neondatabase/infra/pull/1927, we
shipped `io_buffer_alignment=512` to all prod region. The
`AdjacentVectoredReadBuilder` code path is no longer taken and we are
running pageserver unit tests 6 times in the CI. Removing it would
reduce the test duration by 30-60s.
## Summary of changes
- Remove `AdjacentVectoredReadBuilder` code.
- Bump the minimum `io_buffer_alignment` requirement to at least 512
bytes.
- Use default `io_buffer_alignment` for Rust unit tests.
Signed-off-by: Yuchen Liang <yuchen@neon.tech>
Part of #7497, closes#8817.
## Problem
See #8817.
## Summary of changes
**compute_ctl**
- Renew lsn lease as soon as `/configure` updates pageserver_connstr,
use `state_changed` Condvar for synchronization.
**pageserver**
As mentioned in
https://github.com/neondatabase/neon/issues/8817#issuecomment-2315768076,
we still want some permanent error reported if a lease cannot be
granted. By considering attachment mode and the added
`lsn_lease_deadline` when processing lease requests, we can also bound
the case of bad requests to a very short period after migration/restart.
- Refactor https://github.com/neondatabase/neon/pull/9024 and move
`lsn_lease_deadline` to `AttachedTenantConf` so timeline can easily
access it.
- Have separate HTTP `init_lsn_lease` and libpq `renew_lsn_lease` API.
- Always do LSN verification for the initial HTTP lease request.
- LSN verification for the renewal is **still done** when tenants are
not in `AttachedSingle` and we have pass the `lsn_lease_deadline`, which
give plenty of time for compute to renew the lease.
**neon_local**
- add and call `timeline_init_lsn_lease` mgmt_api at static endpoint
start. The initial lsn lease http request is sent when we run `cargo
neon endpoint start <static endpoint>`.
## Testing
- Extend `test_readonly_node_gc` to do pageserver restarts and
migration.
## Future Work
- The control plane should make the initial lease request through HTTP
when creating a static endpoint. This is currently only done in
`neon_local`.
Signed-off-by: Yuchen Liang <yuchen@neon.tech>
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>
## Problem
We get some unexpected errors, but don't know who they're happening for.
## Summary of change
Add tenant id and peer address to PG connection error logs.
Related https://github.com/neondatabase/cloud/issues/17336
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
- In https://github.com/neondatabase/neon/pull/8784, the validate
controller API is modified to check generations directly in the
database. It batches tenants into separate queries to avoid generating a
huge statement, but
- While updating this, I realized that "control_plane_client" is a kind
of confusing name for the client code now that it primarily talks to the
storage controller (the case of talking to the control plane will go
away in a few months).
## Summary of changes
- Big rename to "ControllerUpcallClient" -- this reflects the storage
controller's api naming, where the paths used by the pageserver are in
`/upcall/`
- When sending validate requests, break them up into chunks so that we
avoid possible edge cases of generating any HTTP requests that require
database I/O across many thousands of tenants.
This PR mixes a functional change with a refactor, but the commits are
cleanly separated -- only the last commit is a functional change.
---------
Co-authored-by: Christian Schwarz <christian@neon.tech>
We don't want to allow any new child timelines of archived timelines. If
you want any new child timelines, you should first un-archive the
timeline.
Part of #8088
