On 2014-04-23 16:30:05 -0300, Alvaro Herrera wrote:
> Andres Freund wrote:
>
> > I think this patch is a seriously bad idea. For one, it's not actually
> > doing anything about the problem - the tuple can be accessed without
> > freezing getting involved.
>
> Normal access other than freeze is not a problem, because other code
> paths do check for HEAP_XMAX_INVALID and avoid access to Xmax if that's
> set.
>
> > For another, it will increase wall traffic for freezing of short lived
> > tuples considerably, without any benefit.
>
> True. I didn't actually try to run this; it was just for demonstration
> purposes. It'd need some cooperation from heap_tuple_needs_freeze in
> order to work at all, for one thing.
I think if you want to add something like this it should be added
*inside* the if (MultiXactIdPrecedes(multi, cutoff_multi)) block in
FreezeMultiXactId(). There it seems to make quite a bit of sense.
Greetings,
Andres Freund
-- Andres Freund http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services
