Re: SSI freezing bug

On Mon, Oct 07, 2013 at 12:26:37PM +0300, Heikki Linnakangas wrote:
> When updating a tuple, CheckTargetForConflictsIn() only marks a
> conflict if the transaction holding the predicate lock overlapped
> with the updating transaction.

Ah, this is the bit I was forgetting. (I really ought to have
remembered that, but it's been a while...)

I think it's possible, then, to construct a scenario where a slot is
reused before predicate locks on the old tuple are eligible for
cleanup -- but those locks will never cause a conflict.

So I agree: it's correct to just remove the xmin from the key
unconditionally.

And this is also true:

> And if there's a hole in that thinking I can't see right now,
> the worst that will happen is some unnecessary conflicts, ie. it's
> still correct. It surely can't be worse than upgrading the lock to a
> page-level lock, which would also create unnecessary conflicts.

Dan

-- 
Dan R. K. Ports                UW CSE                http://drkp.net/