Re: Make pg_prewarm, autoprewarm yield for waiting DDL

Hi,

On Mon, Sep 7, 2026 at 8:01 AM Palak Chaturvedi
<chaturvedipalak1911(at)gmail(dot)com> wrote:
>
> I found two other issues while reviewing v3.

Thanks for reviewing it.

> First, 0001 assumes that finding a LOCK in LockMethodLockHash means
> that this backend's fast-path lock has already been transferred and
> therefore has a PROCLOCK. I don't think that is guaranteed.
>
> For example, backend A can hold a weak relation lock through the fast
> path, while backend B acquires the same weak lock through the main
> lock table because its fast-path slots are full. In that case, the
> LOCK exists because of backend B, but backend A still has no PROCLOCK.
> If A calls LockHasWaiters(), 0001 finds the LOCK and then raises:
>
> ERROR: failed to re-find shared proclock object

Ah, you are right. Thanks for catching that. I added a "failed to
re-find shared proclock object" error as a test case in the 0003
patch, in case it's useful. It seems like I didn't fully implement
what Robert suggested here:
https://postgr.es/m/CA%2BTgmob3mVc0LgKNtgy-MdDd9KLffzw1X%3D9qR8UaRmON0xJWNA%40mail.gmail.com.
Fixed in the attached v4, which returns false when our proclock isn't
there instead of erroring out.

> Second, the current CFBot run fails in the Linux 32-bit job. The
> 002_autoprewarm_lock_yield test sets:
>
> shared_buffers = '2GB'
>
> The server then fails during startup with:
>
> FATAL: invalid size -2147483648 for shared memory request for
> "Buffer Blocks"
>
> 0003 describes the test as manual/local, but it is registered in the
> Meson and Make test suites, so CFBot runs it. It either needs a
> portable configuration, an early skip on unsupported builds, or
> should remain unregistered if it is only intended for manual use.

I reduced shared_buffers and relation size to 512MB and about 260MB
respectively and ran the test locally, so I'm not so sure if the CFBot
will be fully happy with it, so I chose to use nocfbot- prefix.

Please find the attached v4 patches.

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