Re: SSI freezing bug

On 2013-10-03 21:14:17 -0700, Dan Ports wrote:
> On Thu, Oct 03, 2013 at 06:19:49AM -0700, Kevin Grittner wrote:
> > Heikki Linnakangas <hlinnakangas@vmware.com> wrote:
> > > IMHO it would be better to remove xmin from the lock key, and vacuum
> > > away the old predicate locks when the corresponding tuple is vacuumed.
> > > The xmin field is only required to handle the case that a tuple is
> > > vacuumed, and a new unrelated tuple is inserted to the same slot.
> > > Removing the lock when the tuple is removed fixes that.
> 
> This seems definitely safe: we need the predicate locks to determine if
> someone is modifying a tuple we read, and certainly if it's eligible
> for vacuum nobody's going to be modifying that tuple anymore.

But we're talking about freezing a tuple, not removing a dead tuple. I
don't see anything preventing modification of a frozen tuple. Right?

Greetings,

Andres Freund

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