Method read_sync

nodedb/src/data/vamana_fetcher.rs:157–184

Submit a single synchronous read for `node_idx` and wait for it. Used as a fallback when `fetch_fp32` is called for a node that was never pre-fetched (e.g. the entry-point seed on first query).

(&mut self, node_idx: u32)

    /// Used as a fallback when `fetch_fp32` is called for a node that was
    /// never pre-fetched (e.g. the entry-point seed on first query).
    fn read_sync(&mut self, node_idx: u32) -> Option<Vec<f32>> {
        let off = vector_offset(&self.layout, node_idx as u64);
        let dim = self.layout.dim as usize;
        let needed = dim * 4;
        let buf_size = align_up(needed, ALIGNMENT);

        let mut buf = AlignedBuf::new(buf_size).ok()?;
        let fd = io_uring::types::Fd(self.file.as_raw_fd());
        let op = io_uring::opcode::Read::new(fd, buf.as_mut_ptr(), buf_size as u32)
            .offset(off)
            .build()
            .user_data(node_idx as u64);

        // SAFETY: `buf` outlives the SQE submission and the wait.
        unsafe {
            self.ring.submission().push(&op).ok()?;
        }
        self.ring.submit_and_wait(1).ok()?;

        let cqe = self.ring.completion().next()?;
        if cqe.result() < needed as i32 {
            return None;
        }

        // SAFETY: io_uring wrote at least `needed` bytes into `buf`.
        let floats = decode_f32_le(unsafe { buf.as_slice(needed) }, dim);
        Some(floats)
    }
}

impl NodeFetcher for IoUringNodeFetcher {