We keep the practice of keeping the compiler up to date, pointing to the
latest release. This is done by many other projects in the Rust
ecosystem as well.
Release notes: https://blog.rust-lang.org/2024/05/02/Rust-1.78.0.html
Prior update was in #7198
part of https://github.com/neondatabase/neon/issues/7124
Changes
-------
This PR replaces the `EphemeralFile::write_blob`-specifc `struct Writer`
with re-use of `owned_buffers_io::write::BufferedWriter`.
Further, it restructures the code to cleanly separate
* the high-level aspect of EphemeralFile's write_blob / read_blk API
* the page-caching aspect
* the aspect of IO
* performing buffered write IO to an underlying VirtualFile
* serving reads from either the VirtualFile or the buffer if it hasn't
been flushed yet
* the annoying "feature" that reads past the end of the written range
are allowed and expected to return zeroed memory, as long as one remains
within one PAGE_SZ
# Problem
On-demand downloads are still using `tokio::fs`, which we know is
inefficient.
# Changes
- Add `pagebench ondemand-download-churn` to quantify on-demand download
throughput
- Requires dumping layer map, which required making `history_buffer`
impl `Deserialize`
- Implement an equivalent of `tokio::io::copy_buf` for owned buffers =>
`owned_buffers_io` module and children.
- Make layer file download sensitive to `io_engine::get()`, using
VirtualFile + above copy loop
- For this, I had to move some code into the `retry_download`, e.g.,
`sync_all()` call.
Drive-by:
- fix missing escaping in `scripts/ps_ec2_setup_instance_store`
- if we failed in retry_download to create a file, we'd try to remove
it, encounter `NotFound`, and `abort()` the process using
`on_fatal_io_error`. This PR adds treats `NotFound` as a success.
# Testing
Functional
- The copy loop is generic & unit tested.
Performance
- Used the `ondemand-download-churn` benchmark to manually test against
real S3.
- Results (public Notion page):
https://neondatabase.notion.site/Benchmarking-tokio-epoll-uring-on-demand-downloads-2024-04-15-newer-code-03c0fdc475c54492b44d9627b6e4e710?pvs=4
- Performance is equivalent at low concurrency. Jumpier situation at
high concurrency, but, still less CPU / throughput with
tokio-epoll-uring.
- It’s a win.
# Future Work
Turn the manual performance testing described in the above results
document into a performance regression test:
https://github.com/neondatabase/neon/issues/7146
