Re: logical changeset generation v6.2

On 22.10.2013 19:12, Andres Freund wrote:
> On 2013-10-18 20:26:16 +0200, Andres Freund wrote:
>> 4) Store both (cmin, cmax) for catalog tuples.
>
> BTW: That would have the nice side-effect of delivering the basis of
> what you need to do parallel sort in a transaction that previously has
> performed DDL.
>
> Currently you cannot do anything in parallel after DDL, even if you only
> scan the table in one backend, because operators et al. have to do
> catalog lookups which you can't do consistently since cmin/cmax aren't
> available in both.

Parallel workers will need cmin/cmax for user tables too, to know which 
tuples are visible to the snapshot.

- Heikki