Re: Restructured Shared Buffer Hash Table

On Tue, Aug 11, 2026 at 9:50 PM Andres Freund <andres(at)anarazel(dot)de> wrote:

> Sspinlocks (neither plain ones nor the buffer header lock variant) have no
> error recovery whatsoever, so any error that is thrown will make the
system
> unusable.

This is a much better reason for not doing complex stuf under the spin lock,
not the number of instruction, but guarantees of safety.

> I don't really understand the race condition this is trying to address:
> > + /* Unlock buffer header after the entry is deleted to avoid a
race condition:

My guess:
Assume we have one bucket a: [a1, a2, a3], and bucket b: [b1]
- invalidate a1
- unlock a1
- reuse a1 as b2
now bucket a will see [a1, b2]
deletion will fail to find a2
Now buckets a and b are linked (in an invalid way).

> You can't just change the nesting in one place, you'd have to change it
> everywhere

Dhruv's patch doesn't change the nesting order. But that is an important
point.

Regards,
Alexandre