Re: Issue with the PRNG used by Postgres

Hi,

On 2024-04-11 21:41:39 -0700, Andres Freund wrote:
> FWIW, I just reproduced the scenario with signals. I added tracking of the
> total time actually slept and lost to SpinDelayStatus, and added a function to
> trigger a wait on a spinlock.
>
> To wait less, I set max_standby_streaming_delay=0.1, but that's just for
> easier testing in isolation. In reality that could have been reached before
> the spinlock is even acquired.
>
> On a standby, while a recovery conflict is happening:
> PANIC: XX000: stuck spinlock detected at crashme, path/to/file:line, after 4.38s, lost 127.96s
>
>
> So right now it's really not hard to trigger the stuck-spinlock logic
> completely spuriously. This doesn't just happen with hot standby, there are
> plenty other sources of lots of signals being sent.

Oh my. There's a workload that completely trivially hits this, without even
trying hard. LISTEN/NOTIFY.

PANIC: XX000: stuck spinlock detected at crashme, file:line, after 0.000072s, lost 133.027159s

Yes, it really triggered in less than 1ms. That was with just one session
doing NOTIFYs from a client. There's plenty users that send NOTIFY from
triggers, which afaics will result in much higher rates of signals being sent.

Even with a bit less NOTIFY traffic, this very obviously gets into the
territory where plain scheduling delays will trigger the stuck spinlock logic.

Greetings,

Andres