mirror of
https://github.com/neondatabase/neon.git
synced 2026-01-07 05:22:56 +00:00
3693d1f431
This is preliminary work for/from #4220 (async `Layer::get_value_reconstruct_data`).
# Full Stack Of Preliminary PRs
Thanks to the countless preliminary PRs, this conversion is relatively
straight-forward.
1. Clean-ups
* https://github.com/neondatabase/neon/pull/4316
* https://github.com/neondatabase/neon/pull/4317
* https://github.com/neondatabase/neon/pull/4318
* https://github.com/neondatabase/neon/pull/4319
* https://github.com/neondatabase/neon/pull/4321
* Note: these were mostly to find an alternative to #4291, which I
thought we'd need in my original plan where we would need to convert
`Tenant::timelines` into an async locking primitive (#4333). In reviews,
we walked away from that, but these cleanups were still quite useful.
2. https://github.com/neondatabase/neon/pull/4364
3. https://github.com/neondatabase/neon/pull/4472
4. https://github.com/neondatabase/neon/pull/4476
5. https://github.com/neondatabase/neon/pull/4477
6. https://github.com/neondatabase/neon/pull/4485
# Significant Changes In This PR
## `compact_level0_phase1` & `create_delta_layer`
This commit partially reverts
"pgserver: spawn_blocking in compaction (#4265)"
4e359db4c7.
Specifically, it reverts the `spawn_blocking`-ificiation of
`compact_level0_phase1`.
If we didn't revert it, we'd have to use `Timeline::layers.blocking_read()`
inside `compact_level0_phase1`. That would use up a thread in the
`spawn_blocking` thread pool, which is hard-capped.
I considered wrapping the code that follows the second
`layers.read().await` into `spawn_blocking`, but there are lifetime
issues with `deltas_to_compact`.
Also, this PR switches the `create_delta_layer` _function_ back to
async, and uses `spawn_blocking` inside to run the code that does sync
IO, while keeping the code that needs to lock `Timeline::layers` async.
## `LayerIter` and `LayerKeyIter` `Send` bounds
I had to add a `Send` bound on the `dyn` type that `LayerIter`
and `LayerKeyIter` wrap. Why? Because we now have the second
`layers.read().await` inside `compact_level0_phase`, and these
iterator instances are held across that await-point.
More background:
https://github.com/neondatabase/neon/pull/4462#issuecomment-1587376960
## `DatadirModification::flush`
Needed to replace the `HashMap::retain` with a hand-rolled variant
because `TimelineWriter::put` is now async.