When we moved throttling up from Timeline::get into page_service,
we stopped being sensitive to `Timeline::cancel`, even though we're
holding a Handle and thus a guard on the `Timeline::gate` open.
This PR rectifies the situation.
Refs
- Found while investigating #10309 (hung detach because gate kept open),
but not expected to be the root cause of that issue because the
affected tenants are not being throttled according to their metrics.
## Problem
Auto-offloading as requested by the compaction task is racy with
unarchival, in that the compaction task might attempt to offload an
unarchived timeline. By that point it will already have set the timeline
to the `Stopping` state however, which makes it unusable for any
purpose. For example:
1. compaction task decides to offload timeline
2. timeline gets unarchived
3. `offload_timeline` gets called by compaction task
* sets timeline's state to `Stopping`
* realizes that the timeline can't be unarchived, errors out
6. endpoint can't be started as the timeline is `Stopping` and thus
'can't be found'.
A future iteration of the compaction task can't "heal" this state either
as the timeline will still not be archived, same goes for other
automatic stuff. The only way to heal this is a tenant detach+attach, or
alternatively a pageserver restart.
Furthermore, the compaction task is especially amenable for such races
as it first stores `can_offload` into a variable, figures out whether
compaction is needed (which takes some time), and only then does it
attempt an offload operation: the time difference between "check" and
"use" is non-trivially small.
To make it even worse, we start the compaction task right after attach
of a tenant, and it is a common pattern by pageserver users to attach a
tenant to then immediately unarchive a timeline, so that an endpoint can
be started.
## Solutions not adopted
The simplest solution is to move the `can_offload` check to right before
attempting of the offload. But this is not a good solution, as no lock
is held between that check and timeline shutdown. So races would still
be possible, just become less likely.
I explored using the timeline state for this, as in adding an additional
enum variant. But `Timeline::set_state` is racy (#10297).
## Adopted solution
We use the lock on the timeline's upload queue as an arbiter: either
unarchival gets to it first and sours the state for auto-offloading, or
auto-offloading shuts it down, which stops any parallel unarchival in
its tracks. The key part is not releasing the upload queue's lock
between the check whether the timeline is archived or not, and shutting
it down (the actual implementation only sets `shutting_down` but it has
the same effect on `initialized_mut()` as a full shutdown). The rest of
the patch is stuff that follows from this.
We also move the part where we set the state to `Stopping` to after that
arbiter has decided the fate of the timeline. For deletions, we do keep
it inside `DeleteTimelineFlow::prepare` however, so that it is called
with all of the the timelines locks held that the function allocates
(timelines lock most importantly). This is only a precautionary measure
however, as I didn't want to analyze deletion related code for possible
races.
## Future changes
It might make sense to move `can_offload` to right before the offload
attempt. Maybe some other properties might have changed as well.
Although this will not be perfect either as no lock is held. I want to
keep it out of this change to emphasize that this move wasn't the main
reason we are race free now.
Fixes#10220
## Problem
If for some reasons we already garbage-collected the data under an LSN
but the caller uses a past LSN for the find_time_cutoff function, now we
will report a missing key error and GC will never proceed.
Note that missing key error can also happen if the key is really missing
(i.e., during the past offload incidents)
## Summary of changes
Make sure GC proceeds by bumping the LSN. When time_cutoff=None, we will
not increase the time_cutoff (it will be set to latest_gc_cutoff). If we
really need to bump the GC LSN for maintenance purpose, we need a
separate API to do that.
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
We have several serious data corruption incidents caused by mismatch of
get-age requests:
https://neondb.slack.com/archives/C07FJS4QF7V/p1723032720164359
We hope that the problem is fixed now. But it is better to prevent such
kind of problems in future.
Part of https://github.com/neondatabase/cloud/issues/16472
## Summary of changes
This PR introduce new V3 version of compute<->pageserver protocol,
adding tag to getpage response.
So now compute is able to check if it really gets response to the
requested page.
## 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>
Co-authored-by: Heikki Linnakangas <heikki@neon.tech>
## Problem
The filtered record metric doesn't make sense for interpreted ingest.
## Summary of changes
While of dubious utility in the first place, this patch replaces them
with records received and records observed metrics for interpreted
ingest:
* received records cause the pageserver to do _something_: write a key,
value pair to storage, update some metadata or flush pending
modifications
* observed records are a shard 0 concept and contain only key metadata
used in tracking relation sizes (received records include observed
records)
## Problem
close https://github.com/neondatabase/neon/issues/10192
## Summary of changes
* `find_gc_time_cutoff` takes `now` parameter so that all branches
compute the cutoff based on the same start time, avoiding races.
* gc-compaction uses a single `get_gc_compaction_watermark` function to
get the safe LSN to compact.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
Co-authored-by: Arpad Müller <arpad-m@users.noreply.github.com>
## Problem
It's not legal to modify layers that are referenced by the current layer
index. Assert this in the upload queue, as preparation for upload queue
reordering.
Touches #10096.
## Summary of changes
Add a debug assertion that the upload queue does not modify layers
referenced by the current index.
I could be convinced that this should be a plain assertion, but will be
conservative for now.
## Problem
Since enabling continuous profiling in staging, we've seen frequent seg
faults. This is suspected to be because jemalloc and pprof-rs take a
stack trace at the same time, and the handlers aren't signal safe.
jemalloc does this probabilistically on every allocation, regardless of
whether someone is taking a heap profile, which means that any CPU
profile has a chance to cause a seg fault.
Touches #10225.
## Summary of changes
For now, just disable heap profiles -- CPU profiles are more important,
and we need to be able to take them without risking a crash.
There is a race condition between `Tenant::shutdown`'s `defuse_for_drop`
loop and `offload_timeline`, where timeline offloading can insert into a
tenant that is in the process of shutting down, in fact so far
progressed that the `defuse_for_drop` has already been called.
This prevents warn log lines of the form:
```
offloaded timeline <hash> was dropped without having cleaned it up at the ancestor
```
The solution piggybacks on the `offloaded_timelines` lock: both the
defuse loop and the offloaded timeline insertion need to acquire the
lock, and we know that the defuse loop only runs after the tenant has
set its `TenantState` to `Stopping`.
So if we hold the `offloaded_timelines` lock, and know that the
`TenantState` is not `Stopping`, then we know that the defuse loop has
not ran yet, and holding the lock ensures that it doesn't start running
while we are inserting the offloaded timeline.
Fixes#10070
## Problem
In https://github.com/neondatabase/neon/pull/9897 we temporarily
disabled the layer valid check because the current one only considers
the end result of all compaction algorithms, but partial gc-compaction
would temporarily produce an "invalid" layer map.
part of https://github.com/neondatabase/neon/issues/9114
## Summary of changes
Allow LSN splits to overlap in the slow path check. Currently, the valid
check is only used in storage scrubber (background job) and during
gc-compaction (without taking layer lock). Therefore, it's fine for such
checks to be a little bit inefficient but more accurate.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
Co-authored-by: Arpad Müller <arpad-m@users.noreply.github.com>
## Problem
We cannot get the size of the compaction queue and access the info.
Part of #9114
## Summary of changes
* Add an API endpoint to get the compaction queue.
* gc_compaction test case now waits until the compaction finishes.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
part of https://github.com/neondatabase/neon/issues/9114
In https://github.com/neondatabase/neon/pull/10127 we fixed the race,
but we didn't add the errors to the allowlist.
## Summary of changes
* Allow repartition errors in the gc-compaction smoke test.
I think it might be worth to refactor the code to allow multiple threads
getting a copy of repartition status (i.e., using Rcu) in the future.
Signed-off-by: Alex Chi Z <chi@neon.tech>
## Problem
Changes in #9786 were functionally complete but missed some edges that
made testing less robust than it should have been:
- `is_key_disposable` didn't consider SLRU dir keys disposable
- Timeline `init_empty` was always creating SLRU dir keys on all shards
The result was that when we had a bug
(https://github.com/neondatabase/neon/pull/10080), it wasn't apparent in
tests, because one would only encounter the issue if running on a
long-lived timeline with enough compaction to drop the initially created
empty SLRU dir keys, _and_ some CLog truncation going on.
Closes: https://github.com/neondatabase/cloud/issues/21516
## Summary of changes
- Update is_key_global and init_empty to handle SLRU dir keys properly
-- the only functional impact is that we avoid writing some spurious
keys in shards >0, but this makes testing much more robust.
- Make `test_clog_truncate` explicitly use a sharded tenant
The net result is that if one reverts #10080, then tests fail (i.e. this
PR is a reproducer for the issue)
## Problem
In #8550, we made the flush loop wait for uploads after every layer.
This was to avoid unbounded buildup of uploads, and to reduce compaction
debt. However, the approach has several problems:
* It prevents upload parallelism.
* It prevents flush and upload pipelining.
* It slows down ingestion even when there is no need to backpressure.
* It does not directly backpressure WAL ingestion (only via
`disk_consistent_lsn`), and will build up in-memory layers.
* It does not directly backpressure based on compaction debt and read
amplification.
An alternative solution to these problems is proposed in #8390.
In the meanwhile, we revert the change to reduce the impact on ingest
throughput. This does reintroduce some risk of unbounded
upload/compaction buildup. Until
https://github.com/neondatabase/neon/issues/8390, this can be addressed
in other ways:
* Use `max_replication_apply_lag` (aka `remote_consistent_lsn`), which
will more directly limit upload debt.
* Shard the tenant, which will spread the flush/upload work across more
Pageservers and move the bottleneck to Safekeeper.
Touches #10095.
## Summary of changes
Remove waiting on the upload queue in the flush loop.
## Problem
close https://github.com/neondatabase/neon/issues/10124
gc-compaction split_gc_jobs is holding the repartition lock for too long
time.
## Summary of changes
* Ensure split_gc_compaction_jobs drops the repartition lock once it
finishes cloning the structures.
* Update comments.
---------
Signed-off-by: Alex Chi Z <chi@neon.tech>
