Re: WAL-based allocation of XIDs is insecure

Ian Lance Taylor <ian(at)airs(dot)com> writes:
> I described myself unclearly. I was suggesting an addition to what
> you are suggesting. The worst case can not be worse.

Then I didn't (and still don't) understand your suggestion. Want to
try again?

> If you are going to allocate a few thousand XIDs each time, then I
> agree that my suggested addition is not worth it. But how do you deal
> with XID wraparound on an unstable system?

About the same as we do now: not very well. But if your system is that
unstable, XID wrap is the least of your worries, I think.

Up through 7.0, Postgres allocated XIDs a thousand at a time, and not
only did the not-yet-used XIDs get lost in a crash, they'd get lost in
a normal shutdown too. What I propose will waste XIDs in a crash but
not in a normal shutdown, so it's still an improvement over prior
versions as far as XID consumption goes.

regards, tom lane