This commit tries to fix regular load spikes on staging, caused by too
many eviction and partial upload operations running at the same time.
Usually it was hapenning after restart, for partial backup the load was
delayed.
- Add a semaphore for evictions (2 permits by default)
- Rename `resident_since` to `evict_not_before` and smooth out the curve
by using random duration
- Use random duration in partial uploads as well
related to https://github.com/neondatabase/neon/issues/6338
some discussion in
https://neondb.slack.com/archives/C033RQ5SPDH/p1720601531744029
We have an issue that some partial uploaded segments can be actually
missing in remote storage. I found this issue when was looking at the
logs in staging, and it can be triggered by failed uploads:
1. Code tries to upload `SEG_TERM_LSN_LSN_sk5.partial`, but receives
error from S3
2. The failed attempt is saved to `segments` vec
3. After some time, the code tries to upload
`SEG_TERM_LSN_LSN_sk5.partial` again
4. This time the upload is successful and code calls `gc()` to delete
previous uploads
5. Since new object and old object share the same name, uploaded data
gets deleted from remote storage
This commit fixes the issue by patching `gc()` not to delete objects
with the same name as currently uploaded.
---------
Co-authored-by: Arpad Müller <arpad-m@users.noreply.github.com>
## Problem
Follow up to https://github.com/neondatabase/neon/pull/8335, to improve
observability of how many evict/restores we are doing.
## Summary of changes
- Add `safekeeper_eviction_events_started_total` and
`safekeeper_eviction_events_completed_total`, with a "kind" label of
evict or restore. This gives us rates, and also ability to calculate how
many are in progress.
- Generalize SafekeeperMetrics test type to use the same helpers as
pageserver, and enable querying any metric.
- Read the new metrics at the end of the eviction test.
## Problem
- The condition for eviction is not time-based: it is possible for a
timeline to be restored in response to a client, that client times out,
and then as soon as the timeline is restored it is immediately evicted
again.
- There is no delay on eviction at startup of the safekeeper, so when it
starts up and sees many idle timelines, it does many evictions which
will likely be immediately restored when someone uses the timeline.
## Summary of changes
- Add `eviction_min_resident` parameter, and use it in
`ready_for_eviction` to avoid evictions if the timeline has been
resident for less than this period.
- This also implicitly delays evictions at startup for
`eviction_min_resident`
- Set this to a very low number for the existing eviction test, which
expects immediate eviction.
The default period is 15 minutes. The general reasoning for that is that
in the worst case where we thrash ~10k timelines on one safekeeper,
downloading 16MB for each one, we should set a period that would not
overwhelm the node's bandwidth.
Fixes https://github.com/neondatabase/neon/issues/6337
Add safekeeper support to switch between `Present` and
`Offloaded(flush_lsn)` states. The offloading is disabled by default,
but can be controlled using new cmdline arguments:
```
--enable-offload
Enable automatic switching to offloaded state
--delete-offloaded-wal
Delete local WAL files after offloading. When disabled, they will be left on disk
--control-file-save-interval <CONTROL_FILE_SAVE_INTERVAL>
Pending updates to control file will be automatically saved after this interval [default: 300s]
```
Manager watches state updates and detects when there are no actvity on
the timeline and actual partial backup upload in remote storage. When
all conditions are met, the state can be switched to offloaded.
In `timeline.rs` there is `StateSK` enum to support switching between
states. When offloaded, code can access only control file structure and
cannot use `SafeKeeper` to accept new WAL.
`FullAccessTimeline` is now renamed to `WalResidentTimeline`. This
struct contains guard to notify manager about active tasks requiring
on-disk WAL access. All guards are issued by the manager, all requests
are sent via channel using `ManagerCtl`. When manager receives request
to issue a guard, it unevicts timeline if it's currently evicted.
Fixed a bug in partial WAL backup, it used `term` instead of
`last_log_term` previously.
After this commit is merged, next step is to roll this change out, as in
issue #6338.
