After https://github.com/neondatabase/neon/pull/8022 was deployed to
staging, I noticed many cases of timeouts. After inspecting the logs, I
realized that some operations are taking ~20 seconds and they're doing
while holding shared state lock. Usually it happens right after
redeploy, because compute reconnections put high load on disks. This
commit tries to improve observability around slow operations.
Non-observability changes:
- `TimelineState::finish_change` now skips update if nothing has changed
- `wal_residence_guard()` timeout is set to 30s
This is a preparation for #8022, to make the PR both backwards and
foward compatible.
This commit adds `eviction_state` field to control file. Adds support
for reading it, but writes control file in old format where possible, to
keep the disk format forward compatible.
Note: in `patch_control_file`, new field gets serialized to json like
this:
- `"eviction_state": "Present"`
- `"eviction_state": {"Offloaded": "0/8F"}`
Add support for backing up partial segments to remote storage. Disabled
by default, can be enabled with `--partial-backup-enabled`.
Safekeeper timeline has a background task which is subscribed to
`commit_lsn` and `flush_lsn` updates. After the partial segment was
updated (`flush_lsn` was changed), the segment will be uploaded to S3 in
about 15 minutes.
The filename format for partial segments is
`Segment_Term_Flush_Commit_skNN.partial`, where:
- `Segment` – the segment name, like `000000010000000000000001`
- `Term` – current term
- `Flush` – flush_lsn in hex format `{:016X}`, e.g. `00000000346BC568`
- `Commit` – commit_lsn in the same hex format
- `NN` – safekeeper_id, like `1`
The full object name example:
`000000010000000000000002_2_0000000002534868_0000000002534410_sk1.partial`
Each safekeeper will keep info about remote partial segments in its
control file. Code updates state in the control file before doing any S3
operations. This way control file stores information about all
potentially existing remote partial segments and can clean them up after
uploading a newer version.
Closes#6336
safekeeper.rs is mostly about consensus, but state is wider. Also form
SafekeeperState which encapsulates persistent part + in memory layer with API
for atomic updates.
Moves remote_consistent_lsn back to SafekeeperMemState, fixes its absense from
memory dump.
Also renames SafekeeperState to TimelinePersistentState, as TimelineMemState and
TimelinePersistent state are created.
