Re: Speed up COPY FROM text/CSV parsing using SIMD

Hi,

On Mon, 7 Sept 2026 at 19:29, Nazir Bilal Yavuz <byavuz81(at)gmail(dot)com> wrote:
>
> When fewer than one SIMD vector of bytes (16 in this case) remain
> buffered, CopyReadLineTextSIMDHelper() refills the input before
> falling back to scalar parsing. If those buffered bytes already
> contain a complete '\.' (end-of-copy marker) and the source is an open
> FIFO with no more data, the refill blocks, so COPY fails to recognize
> the marker until more data arrives or the writer closes the FIFO.
> Reproducer SQL script is attached, you can see that this causes a
> hang.
>
> One potential fix is checking for an end-of-copy marker when fewer
> than one SIMD vector of bytes remains in the buffer and we decide to
> load more data into it. I haven't benchmarked this solution yet but it
> could potentially cause a slowdown when we load data in smaller
> chunks. Otherwise, I don't think this solution will cause a slowdown.
> I am planning to work on this tomorrow.
>
> Any opinions on the bug or the potential solution?

Here is an attempt to solve this problem. I ran Manni's script and saw
a 1-2% slowdown on TEXT-wide inputs. It is still faster compared to
the version without the SIMD patch; the slowdown is relative to the
current master branch (which includes the SIMD patch).

--
Regards,
Nazir Bilal Yavuz
Microsoft