Going through the list of recent flaky tests, trying to fix those
related to graceful shutdown.
- test_forward_compatibility: flush and wait for uploads to avoid
graceful shutdown
- test_layer_bloating: in the end the endpoint and vanilla are still up
=> immediate shutdown
- test_lagging_sk: pageserver shutdown is not related to the test =>
immediate shutdown
- test_lsn_lease_size: pageserver flushing is not needed => immediate
shutdown
Additionally:
- remove `wait_for_upload` usage from workload fixture
Cc: #8708Fixes: #8710
## Problem
We want to run our regression test suite on ARM.
## Summary of changes
- run regression tests on release ARM builds
- run `build-neon` (including rust tests) on debug ARM builds
- add `arch` parameter to test to distinguish them in the allure report
and in a database
## Problem
The default Postgres version is set to 15 in code, while we use 16 in
most of the other places (and Postgres 17 is coming)
## Summary of changes
- Run `benchmarks` job with Postgres 16 (instead of Postgres 14)
- Set `DEFAULT_PG_VERSION` to 16 in all places
- Remove deprecated `--pg-version` pytest argument
- Update `test_metadata_bincode_serde_ensure_roundtrip` for Postgres 16
Migrates most of the remaining parts of the scrubber to remote_storage:
* `pageserver_physical_gc`
* `scan_metadata` for pageservers (safekeepers were done in #8595)
* `download()` in `tenant_snapshot`. The main `tenant_snapshot` is not
migrated as it uses version history to be able to work in the face of
ongoing changes.
Part of #7547
After the rollout has succeeded, we now set the default image
compression to be enabled.
We also remove its explicit mention from `neon_fixtures.py` added in
#8368 as it is now the default (and we switch to `zstd(1)` which is a
bit nicer on CPU time).
Part of https://github.com/neondatabase/neon/issues/5431
## Problem
https://github.com/neondatabase/neon/pull/8588 implemented the mechanism
for storage controller
leadership transfers. However, there's no tests that exercise the
behaviour.
## Summary of changes
1. Teach `neon_local` how to handle multiple storage controller
instances. Each storage controller
instance gets its own subdirectory (`storage_controller_1, ...`).
`storage_controller start|stop` subcommands
have also been extended to optionally accept an instance id.
2. Add a storage controller proxy test fixture. It's a basic HTTP server
that forwards requests from pageserver
and test env to the currently configured storage controller.
3. Add a test which exercises storage controller leadership transfer.
4. Finally fix a couple bugs that the test surfaced
## Problem
The control file contains the id of the safekeeper that uploaded it.
Previously, when sending a snapshot of the control file to another sk,
it would eventually be gc-ed by the receiving sk. This is incorrect
because the original sk might still need it later.
## Summary of Changes
When sending a snapshot and the control file contains an uploaded
segment:
* Create a copy of the segment in s3 with the destination sk in the
object name
* Tweak the streamed control file to point to the object create in the
previous step
Note that the snapshot endpoint now has to know the id of the requestor,
so the api has been extended to include the node if of the destination
sk.
Closes https://github.com/neondatabase/neon/issues/8542
After #8655 we've had a few issues (mostly tracked on #8708) with the
graceful shutdown. In order to shutdown more of the processes and catch
more errors, for example, from all pageservers, do an immediate shutdown
for those nodes which fail the initial (possibly graceful) shutdown.
Cc: #6485
A few of the benchmarks have started failing after #8655 where they are
waiting for compactor task. Reads done by image layer creation should
already be cancellation sensitive because vectored get does a check each
time, but try sprinkling additional cancellation points to:
- each partition
- after each vectored read batch
It should give us all possible allowed_errors more consistently.
While getting the workflows to pass on
https://github.com/neondatabase/neon/pull/8632 it was noticed that
allowed_errors are rarely hit (1/4). This made me realize that we always
do an immediate stop by default. Doing a graceful shutdown would had
made the draining more apparent and likely we would not have needed the
#8632 hotfix.
Downside of doing this is that we will see more timeouts if tests are
randomly leaving pause failpoints which fail the shutdown.
The net outcome should however be positive, we could even detect too
slow shutdowns caused by a bug or deadlock.
## Problem
This test was disabled.
## Summary of changes
- Remove the skip marker.
- Explicitly avoid doing compaction & gc during checkpoints (the default
scale doesn't do anything here, but when experimeting with larger scales
it messes things up)
- Set a data size that gives a ~20s runtime on a Hetzner dev machine,
previous one gave very noisy results because it was so small
For reference on a Hetzner AX102:
```
------------------------------ Benchmark results -------------------------------
test_bulk_insert[neon-release-pg16].insert: 25.664 s
test_bulk_insert[neon-release-pg16].pageserver_writes: 5,428 MB
test_bulk_insert[neon-release-pg16].peak_mem: 577 MB
test_bulk_insert[neon-release-pg16].size: 0 MB
test_bulk_insert[neon-release-pg16].data_uploaded: 1,922 MB
test_bulk_insert[neon-release-pg16].num_files_uploaded: 8
test_bulk_insert[neon-release-pg16].wal_written: 1,382 MB
test_bulk_insert[neon-release-pg16].wal_recovery: 25.373 s
test_bulk_insert[neon-release-pg16].compaction: 0.035 s
```
It should take syncrep flush_lsn into account because WAL before it on endpoint
restart is lost, which makes replication miss some data if slot had already been
advanced too far. This commit adds test reproducing the issue and bumps
vendor/postgres to commit with the actual fix.
Noticed this while debugging a test failure in #8673 which only occurs
with real S3 instead of mock S3: if you authenticate to S3 via
`AWS_PROFILE`, then it requires the `HOME` env var to be set so that it
can read inside the `~/.aws` directory.
The scrubber abstraction `StorageScrubber::scrubber_cli` in
`neon_fixtures.py` would otherwise not work. My earlier PR #6556 has
done similar things for the `neon_local` wrapper.
You can try:
```
aws sso login --profile dev
export ENABLE_REAL_S3_REMOTE_STORAGE=y REMOTE_STORAGE_S3_BUCKET=neon-github-ci-tests REMOTE_STORAGE_S3_REGION=eu-central-1 AWS_PROFILE=dev
RUST_BACKTRACE=1 BUILD_TYPE=debug DEFAULT_PG_VERSION=16 ./scripts/pytest -vv --tb=short -k test_scrubber_tenant_snapshot
```
before and after this patch: this patch fixes it.
## Problem
Migrations of tenant shards with cold secondaries are holding up drains
in during production deployments.
## Summary of changes
If a secondary locations is lagging by more than 256MiB (configurable,
but that's the default), then skip cutting it over to the secondary as part of the node drain.
Earlier I was thinking we'd need a (ancestor_lsn, timeline_id) ordered
list of reparented. Turns out we did not need it at all. Replace it with
an unordered hashset. Additionally refactor the reparented direct
children query out, it will later be used from more places.
Split off from #8430.
Cc: #6994
Part of #8128.
## Problem
Currently, scrubber `scan_metadata` command will return with an error
code if the metadata on remote storage is corrupted with fatal errors.
To safely deploy this command in a cronjob, we want to differentiate
between failures while running scrubber command and the erroneous
metadata. At the same time, we also want our regression tests to catch
corrupted metadata using the scrubber command.
## Summary of changes
- Return with error code only when the scrubber command fails
- Uses explicit checks on errors and warnings to determine metadata
health in regression tests.
**Resolve conflict with `tenant-snapshot` command (after shard split):**
[`test_scrubber_tenant_snapshot`](https://github.com/neondatabase/neon/blob/yuchen/scrubber-scan-cleanup-before-prod/test_runner/regress/test_storage_scrubber.py#L23)
failed before applying 422a8443dd
- When taking a snapshot, the old `index_part.json` in the unsharded
tenant directory is not kept.
- The current `list_timeline_blobs` implementation consider no
`index_part.json` as a parse error.
- During the scan, we are only analyzing shards with highest shard
count, so we will not get a parse error. but we do need to add the
layers to tenant object listing, otherwise we will get index is
referencing a layer that is not in remote storage error.
- **Action:** Add s3_layers from `list_timeline_blobs` regardless of
parsing error
Signed-off-by: Yuchen Liang <yuchen@neon.tech>
## Problem
Sometimes, a layer is Covered by hasn't yet been evicted from local disk
(e.g. shortly after image layer generation). It is not good use of
resources to download these to a secondary location, as there's a good
chance they will never be read.
This follows the previous change that added layer visibility:
- #8511
Part of epic:
- https://github.com/neondatabase/neon/issues/8398
## Summary of changes
- When generating heatmaps, only include Visible layers
- Update test_secondary_downloads to filter to visible layers when
listing layers from an attached location
## Problem
We need to test the logical replication with some external consumers.
## Summary of changes
A test of the logical replication with Debezium as a consumer was added.
---------
Co-authored-by: Alexander Bayandin <alexander@neon.tech>
Currently, we do not have facilities to persistently block GC on a
tenant for whatever reason. We could do a tenant configuration update,
but that is risky for generation numbers and would also be transient.
Introduce a `gc_block` facility in the tenant, which manages per
timeline blocking reasons.
Additionally, add HTTP endpoints for enabling/disabling manual gc
blocking for a specific timeline. For debugging, individual tenant
status now includes a similar string representation logged when GC is
skipped.
Cc: #6994
## Problem
> Currently, long-running LR tests recreate endpoints every night. We'd
like to have along-running buildup of history to exercise the pageserver
in this case (instead of "unit-testing" the same behavior everynight).
Closes#8317
## Summary of changes
- Update Postgres version for replication tests
- Set `BENCHMARK_PROJECT_ID_PUB`/`BENCHMARK_PROJECT_ID_SUB` env vars to
projects that were created for this purpose
---------
Co-authored-by: Sasha Krassovsky <krassovskysasha@gmail.com>
Makes `flush_frozen_layer` add a barrier to the upload queue and makes
it wait for that barrier to be reached until it lets the flushing be
completed.
This gives us backpressure and ensures that writes can't build up in an
unbounded fashion.
Fixes#7317
## Problem
`allure_attach_from_dir` method might create `tar.zst` archives even
if `--alluredir` is not set (i.e. Allure results collection is disabled)
## Summary of changes
- Don't run `allure_attach_from_dir` if `--alluredir` is not set
## Problem
We recently added a "visibility" state to layers, but nothing
initializes it.
Part of:
- #8398
## Summary of changes
- Add a dependency on `range-set-blaze`, which is used as a fast
incrementally updated alternative to KeySpace. We could also use this to
replace the internals of KeySpaceRandomAccum if we wanted to. Writing a
type that does this kind of "BtreeMap & merge overlapping entries" thing
isn't super complicated, but no reason to write this ourselves when
there's a third party impl available.
- Add a function to layermap to calculate visibilities for each layer
- Add a function to Timeline to call into layermap and then apply these
visibilities to the Layer objects.
- Invoke the calculation during startup, after image layer creations,
and when removing branches. Branch removal and image layer creation are
the two ways that a layer can go from Visible to Covered.
- Add unit test & benchmark for the visibility calculation
- Expose `pageserver_visible_physical_size` metric, which should always
be <= `pageserver_remote_physical_size`.
- This metric will feed into the /v1/utilization endpoint later: the
visible size indicates how much space we would like to use on this
pageserver for this tenant.
- When `pageserver_visible_physical_size` is greater than
`pageserver_resident_physical_size`, this is a sign that the tenant has
long-idle branches, which result in layers that are visible in
principle, but not used in practice.
This does not keep visibility hints up to date in all cases:
particularly, when creating a child timeline, any previously covered
layers will not get marked Visible until they are accessed.
Updates after image layer creation could be implemented as more of a
special case, but this would require more new code: the existing depth
calculation code doesn't maintain+yield the list of deltas that would be
covered by an image layer.
## Performance
This operation is done rarely (at startup and at timeline deletion), so
needs to be efficient but not ultra-fast.
There is a new `visibility` bench that measures runtime for a synthetic
100k layers case (`sequential`) and a real layer map (`real_map`) with
~26k layers.
The benchmark shows runtimes of single digit milliseconds (on a ryzen
7950). This confirms that the runtime shouldn't be a problem at startup
(as we already incur S3-level latencies there), but that it's slow
enough that we definitely shouldn't call it more often than necessary,
and it may be worthwhile to optimize further later (things like: when
removing a branch, only bother scanning layers below the branchpoint)
```
visibility/sequential time: [4.5087 ms 4.5894 ms 4.6775 ms]
change: [+2.0826% +3.9097% +5.8995%] (p = 0.00 < 0.05)
Performance has regressed.
Found 24 outliers among 100 measurements (24.00%)
2 (2.00%) high mild
22 (22.00%) high severe
min: 0/1696070, max: 93/1C0887F0
visibility/real_map time: [7.0796 ms 7.0832 ms 7.0871 ms]
change: [+0.3900% +0.4505% +0.5164%] (p = 0.00 < 0.05)
Change within noise threshold.
Found 4 outliers among 100 measurements (4.00%)
3 (3.00%) high mild
1 (1.00%) high severe
min: 0/1696070, max: 93/1C0887F0
visibility/real_map_many_branches
time: [4.5285 ms 4.5355 ms 4.5434 ms]
change: [-1.0012% -0.8004% -0.5969%] (p = 0.00 < 0.05)
Change within noise threshold.
```
Part of #8128, followup to #8480. closes#8421.
Enable scrubber to optionally post metadata scan health results to
storage controller.
Signed-off-by: Yuchen Liang <yuchen@neon.tech>
Part of #8128, followed by #8502.
## Problem
Currently we lack mechanism to alert unhealthy `scan_metadata` status if
we start running this scrubber command as part of a cronjob. With the
storage controller client introduced to storage scrubber in #8196, it is
viable to set up alert by storing health status in the storage
controller database.
We intentionally do not store the full output to the database as the
json blobs potentially makes the table really huge. Instead, only a
health status and a timestamp recording the last time metadata health
status is posted on a tenant shard.
Signed-off-by: Yuchen Liang <yuchen@neon.tech>
## Problem
After https://github.com/neondatabase/neon/pull/7990 `regress_test` job
started to fail with an error:
```
...
File "/__w/neon/neon/test_runner/fixtures/benchmark_fixture.py", line 485, in pytest_terminal_summary
terminalreporter.write(f"{test_report.head_line}.{recorded_property['name']}: ")
TypeError: 'bool' object is not subscriptable
```
https://github.com/neondatabase/neon/actions/runs/10125750938/job/28002582582
It happens because the current implementation doesn't expect pytest's
`user_properties` can be used for anything else but benchmarks (and
https://github.com/neondatabase/neon/pull/7990 started to use it for
tracking `preserve_database_files` parameter)
## Summary of changes
- Make NeonBenchmarker use only records with`neon_benchmarker_` prefix
## Problem
There's a `NeonEnvBuilder#preserve_database_files` parameter that allows
you to keep database files for debugging purposes (by default, files get
cleaned up), but there's no way to get these files from a CI run.
This PR adds handling of `NeonEnvBuilder#preserve_database_files` and
adds the compressed test output directory to Allure reports (for tests
with this parameter enabled).
Ref https://github.com/neondatabase/neon/issues/6967
## Summary of changes
- Compress and add the whole test output directory to Allure reports
- Currently works only with `neon_env_builder` fixture
- Remove `preserve_database_files = True` from sharding tests as
unneeded
---------
Co-authored-by: Christian Schwarz <christian@neon.tech>
## Problem
We are missing the step-down primitive required to implement rolling
restarts of the storage controller.
## Summary of changes
Add `/control/v1/step_down` endpoint which puts the storage controller
into a state where it rejects
all API requests apart from `/control/v1/step_down`, `/status` and
`/metrics`. When receiving the request,
storage controller cancels all pending reconciles and waits for them to
exit gracefully. The response contains
a snapshot of the in-memory observed state.
Related:
* https://github.com/neondatabase/cloud/issues/14701
* https://github.com/neondatabase/neon/issues/7797
* https://github.com/neondatabase/neon/pull/8310
## Problem
Vectored get is already enabled in all prod regions without validation.
The pageserver defaults
are out of sync however.
## Summary of changes
Update the pageserver defaults to match the prod config. Also means that
when running tests locally,
people don't have to use the env vars to get the prod config.
## Problem
Currently, tests may have a scrub during teardown if they ask for it,
but most tests don't request it. To detect "unknown unknowns", let's run
it at the end of every test where possible. This is similar to asserting
that there are no errors in the log at the end of tests.
## Summary of changes
- Remove explicit `enable_scrub_on_exit`
- Always scrub if remote storage is an S3Storage.
## Problem
Re-attach blocks the pageserver http server from starting up. Hence, it
can't reply to heartbeats
until that's done. This makes the storage controller mark the node
off-line (not good). We worked
around this by setting the interval after which nodes are marked offline
to 5 minutes. This isn't a
long term solution.
## Summary of changes
* Introduce a new `NodeAvailability` state: `WarmingUp`. This state
models the following time interval:
* From receiving the re-attach request until the pageserver replies to
the first heartbeat post re-attach
* The heartbeat delta generator becomes aware of this state and uses a
separate longer interval
* Flag `max-warming-up-interval` now models the longer timeout and
`max-offline-interval` the shorter one to
match the names of the states
Closes https://github.com/neondatabase/neon/issues/7552
## Problem
In `test_basebackup_with_high_slru_count`, the pageserver is sometimes
mysteriously hanging on startup, having been started+stopped earlier in
the test setup while populating template tenant data.
- #7586
We can't see why this is hanging in this particular test. The test does
some weird stuff though, like attaching a load of broken tenants and
then doing a SIGQUIT kill of a pageserver.
## Summary of changes
- Attach tenants normally instead of doing a failpoint dance to attach
them as broken
- Shut the pageserver down gracefully during init instead of using
immediate mode
- Remove the "sequential" variant of the unstable test, as this is going
away soon anyway
- Log before trying to acquire lock file, so that if it hangs we have a
clearer sense of if that's really where it's hanging. It seems like it
is, but that code does a non-blocking flock so it's surprising.
## Problem
`test_change_pageserver` stops pageservers in a way that can overlap
with the controller's heartbeats: the controller can get a heartbeat
success and then immediately find the node unavailable. This particular
situation triggers a log that isn't in our current allow-list of
messages for nodes offline
Example:
https://neon-github-public-dev.s3.amazonaws.com/reports/pr-8339/10048487700/index.html#testresult/19678f27810231df/retries
## Summary of changes
- Add the message to the allow list
## Problem
This test sometimes found that ancestors were getting cleaned up before
it had done any compaction.
Compaction was happening implicitly via Workload.
Example:
https://neon-github-public-dev.s3.amazonaws.com/reports/pr-8298/10032173390/index.html#testresult/fb04786402f80822/retries
## Summary of changes
- Set upload=False when writing data after shard split, to avoid doing a
checkpoint
- Add a checkpoint_period & explicit wait for uploads so that we ensure
data lands in S3 without doing a checkpoint
Part of #8128.
## Problem
Scrubber uses `scan_metadata` command to flag metadata inconsistencies.
To trust it at scale, we need to make sure the errors we emit is a
reflection of real scenario. One check performed in the scrubber is to
see whether layers listed in the latest `index_part.json` is present in
object listing. Currently, the scrubber does not robustly handle the
case where objects are uploaded/deleted during the scan.
## Summary of changes
**Condition for success:** An object in the index is (1) in the object
listing we acquire from S3 or (2) found in a HeadObject request (new
object).
- Add in the `HeadObject` requests for the layers missing from the
object listing.
- Keep the order of first getting the object listing and then
downloading the layers.
- Update check to only consider shards with highest shard count.
- Skip analyzing a timeline if `deleted_at` tombstone is marked in
`index_part.json`.
- Add new test to see if scrubber actually detect the metadata
inconsistency.
_Misc_
- A timeline with no ancestor should always have some layers.
- Removed experimental histograms
_Caveat_
- Ancestor layer is not cleaned until #8308 is implemented. If ancestor
layers reference non-existing layers in the index, the scrubber will
emit false positives.
Signed-off-by: Yuchen Liang <yuchen@neon.tech>
## Problem
After a shard split, the pageserver leaves the ancestor shard's content
in place. It may be referenced by child shards, but eventually child
shards will de-reference most ancestor layers as they write their own
data and do GC. We would like to eventually clean up those ancestor
layers to reclaim space.
## Summary of changes
- Extend the physical GC command with `--mode=full`, which includes
cleaning up unreferenced ancestor shard layers
- Add test `test_scrubber_physical_gc_ancestors`
- Remove colored log output: in testing this is irritating ANSI code
spam in logs, and in interactive use doesn't add much.
- Refactor storage controller API client code out of storcon_client into
a `storage_controller/client` crate
- During physical GC of ancestors, call into the storage controller to
check that the latest shards seen in S3 reflect the latest state of the
tenant, and there is no shard split in progress.
Successor of #8288 , just enable zstd in tests. Also adds a test that
creates easily compressable data.
Part of #5431
---------
Co-authored-by: John Spray <john@neon.tech>
Co-authored-by: Joonas Koivunen <joonas@neon.tech>
## Problem
Ahead of enabling eviction in the field, where it will become the
normal/default mode, let's enable it by default throughout our tests in
case any issues become visible there.
## Summary of changes
- Make default `extra_opts` for safekeepers enable offload & deletion
- Set low timeouts in `extra_opts` so that tests running for tens of
seconds have a chance to hit some of these background operations.
When `NeonEnv.from_repo_dir` was introduced, storage controller stored
its
state exclusively `attachments.json`.
Since then, it has moved to using Postgres, which stores its state in
`storage_controller_db`.
But `NeonEnv.from_repo_dir` wasn't adjusted to do this.
This PR rectifies the situation.
Context for this is failures in
`test_pageserver_characterize_throughput_with_n_tenants`
CF:
https://neondb.slack.com/archives/C033RQ5SPDH/p1721035799502239?thread_ts=1720901332.293769&cid=C033RQ5SPDH
Notably, `from_repo_dir` is also used by the backwards- and
forwards-compatibility.
Thus, the changes in this PR affect those tests as well.
However, it turns out that the compatibility snapshot already contains
the `storage_controller_db`.
Thus, it should just work and in fact we can remove hacks like
`fixup_storage_controller`.
Follow-ups created as part of this work:
* https://github.com/neondatabase/neon/issues/8399
* https://github.com/neondatabase/neon/issues/8400
## Problem
We lack insight into:
- How much of a tenant's physical size is image vs. delta layers
- Average sizes of image vs. delta layers
- Total layer counts per timeline, indicating size of index_part object
As well as general observability love, this is motivated by
https://github.com/neondatabase/neon/issues/6738, where we need to
define some sensible thresholds for storage amplification, and using
total physical size may not work well (if someone does a lot of DROPs
then it's legitimate for the physical-synthetic ratio to be huge), but
the ratio between image layer size and delta layer size may be a better
indicator of whether we're generating unreasonable quantities of image
layers.
## Summary of changes
- Add pageserver_layer_bytes and pageserver_layer_count metrics,
labelled by timeline and `kind` (delta or image)
- Add & subtract these with LayerInner's lifetime.
I'm intentionally avoiding using a generic metric RAII guard object, to
avoid bloating LayerInner: it already has all the information it needs
to update metric on new+drop.
This test reproduces the case of a writer creating a deep stack of L0
layers. It uses realistic layer sizes and writes several gigabytes of
data, therefore runs as a performance test although it is validating
memory footprint rather than performance per se.
It acts a regression test for two recent fixes:
- https://github.com/neondatabase/neon/pull/8401
- https://github.com/neondatabase/neon/pull/8391
In future it will demonstrate the larger improvement of using a k-merge
iterator for L0 compaction (#8184)
This test can be extended to enforce limits on the memory consumption of
other housekeeping steps, by restarting the pageserver and then running
other things to do the same "how much did RSS increase" measurement.
As described in #8385, the likely source for flakiness in
test_tenant_creation_fails is the following sequence of events:
1. test instructs the storage controller to create the tenant
2. storage controller adds the tenant and persists it to the database.
issues a creation request
3. the pageserver restarts with the failpoint disabled
4. storage controller's background reconciliation still wants to create
the tenant
5. pageserver gets new request to create the tenant from background
reconciliation
This commit just avoids the storage controller entirely. It has its own
set of issues, as the re-attach request will obviously not include the
tenant, but it's still useful to test for non-existence of the tenant.
The generation is also not optional any more during tenant attachment.
If you omit it, the pageserver yields an error. We change the signature
of `tenant_attach` to reflect that.
Alternative to #8385Fixes#8266
Right now timeline detach ancestor reports an error (409, "no ancestor")
on a new attempt after successful completion. This makes it troublesome
for storage controller retries. Fix it to respond with `200 OK` as if
the operation had just completed quickly.
Additionally, the returned timeline identifiers in the 200 OK response
are now ordered so that responses between different nodes for error
comparison are done by the storage controller added in #8353.
Design-wise, this PR introduces a new strategy for accessing the latest
uploaded IndexPart:
`RemoteTimelineClient::initialized_upload_queue(&self) ->
Result<UploadQueueAccessor<'_>, NotInitialized>`. It should be a more
scalable way to query the latest uploaded `IndexPart` than to add a
query method for each question directly on `RemoteTimelineClient`.
GC blocking will need to be introduced to make the operation fully
idempotent. However, it is idempotent for the cases demonstrated by
tests.
Cc: #6994
