refactor(blob_io): use owned buffers #6660
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We can probably get rid of the entire trait, but, that's for another time.
…uilder-refactor' into problame/integrate-tokio-epoll-uring/write-path/simplify-write-at-api
This reverts commit b5a00b0.
…ath/refactor-blob-writer
2430 tests run: 2319 passed, 0 failed, 111 skipped (full report)Code coverage (full report)
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4227e42 at 2024-02-12T13:59:49.623Z :recycle: |
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| io_buf, | ||
| Err(Error::new( | ||
| ErrorKind::Other, | ||
| format!("blob too large ({} bytes)", len), |
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| format!("blob too large ({} bytes)", len), | |
| format!("blob too large ({len} bytes)"), |
| let mut len_buf = (len as u32).to_be_bytes(); | ||
| len_buf[0] |= 0x80; | ||
| io_buf.extend_from_slice(&len_buf[..]); | ||
| self.write_all(io_buf).await |
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the write call can be moved out of the if as both branches have it.
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| let mut io_buf = self.io_buf.take().expect("we always put it back below"); | ||
| io_buf.clear(); | ||
| let (io_buf, hdr_res) = async { |
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it's not 100% clear to me why there is an async block here. It would be useful to have a comment that explains it also for other future readers. I suppose some ownership/borrow checker issue?
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This PR refactors the `blob_io` code away from using slices towards taking owned buffers and return them after use. Using owned buffers will eventually allow us to use io_uring for writes. part of #6663 Depends on neondatabase/tokio-epoll-uring#43 The high level scheme is as follows: - call writing functions with the `BoundedBuf` - return the underlying `BoundedBuf::Buf` for potential reuse in the caller NB: Invoking `BoundedBuf::slice(..)` will return a slice that _includes the uninitialized portion of `BoundedBuf`_. I.e., the portion between `bytes_init()` and `bytes_total()`. It's a safe API that actually permits access to uninitialized memory. Not great. Another wrinkle is that it panics if the range has length 0. However, I don't want to switch away from the `BoundedBuf` API, since it's what tokio-uring uses. We can always weed this out later by replacing `BoundedBuf` with our own type. Created an issue so we don't forget: neondatabase/tokio-epoll-uring#46
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For the record, @arpad-m and I had a call where I explained the questions above. |
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The call addressed my first two concerns, which turn out to be due to shortcomings in the API. The three last comments in the review still apply though. Would be great to have a followup PR for them, but not extremely neccessary as they are just nits. |
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This PR refactors the
blob_iocode away from using slices towards taking owned buffers and return them after use.Using owned buffers will eventually allow us to use io_uring for writes.
part of #6663
Depends on neondatabase/tokio-epoll-uring#43
The high level scheme is as follows:
BoundedBufBoundedBuf::Buffor potential reuse in the callerNB: Invoking
BoundedBuf::slice(..)will return a slice that includes the uninitialized portion ofBoundedBuf.I.e., the portion between
bytes_init()andbytes_total().It's a safe API that actually permits access to uninitialized memory.
Not great.
Another wrinkle is that it panics if the range has length 0.
However, I don't want to switch away from the
BoundedBufAPI, since it's what tokio-uring uses.We can always weed this out later by replacing
BoundedBufwith our own type.Created an issue so we don't forget: neondatabase/tokio-epoll-uring#46