Re: Be strict when request to flush past end of WAL in WaitXLogInsertionsToFinish

Hi,

On Thu, Sep 3, 2026 at 5:05 PM Paul Kim <mok03127(at)gmail(dot)com> wrote:
>
> Thanks, both. Attached is v2: 0001 is the fix, unchanged from v1, and
> 0002 adds the reproducer as a TAP test on HEAD.
>
> The test adds a small module, src/test/modules/test_walwriter, with one
> C function that requests a segment switch and then stores the resulting
> insert position in asyncXactLSN. After a switch that position is just
> past the new segment's long page header, beyond the end of generated
> WAL, so the walwriter's next cycle requests a flush past the end of
> generated WAL -- the same shape as the production request.
>
> I did look at injection points first, but there is no INJECTION_POINT()
> in this path, and what the reproducer needs is a bogus value stored
> into asyncXactLSN rather than a backend stopped at a particular point,
> which would require a custom callback and hence a test module anyway.

Thanks for the v2 patches. Just curious, how did the bogus LSN end up
in asyncXactLSN in production when you hit the issue?

--
Bharath Rupireddy
Amazon Web Services: https://aws.amazon.com