Re: Synchronized snapshots versus multiple databases

On Oct21, 2011, at 19:47 , Robert Haas wrote:
> On Fri, Oct 21, 2011 at 1:40 PM, Florian Pflug <fgp@phlo.org> wrote:
>> AFAIR, the performance hit we'd take by making the vacuum cutoff point
>> (i.e. GetOldestXmin()) global instead of database-local has been repeatedly
>> used in the past as an against against cross-database queries. I have to
>> admit that I currently cannot seem to find an entry in the archives to
>> back that up, though.

> I haven't seen anyone explain why they really need this feature
> anyway, and I think it's going in the wrong direction.  IMHO, anyone
> who wants to be doing cross-database queries should be using schemas
> instead, and if that's not workable for some reason, then we should
> improve the schema implementation until it becomes workable.  I think
> that the target use case for separate databases ought to be
> multi-tenancy, but what is needed there is actually more isolation
> (e.g. wrt/role names, cluster-wide visibility of pg_database contents,
> etc.), not less.

Agreed. I wasn't trying to argue for cross-database queries - quite the opposite,
actually. My point was more that since we've used database isolation as an
argument against cross-database queries in the past, we shouldn't sacrifice
it now for synchronized snapshots.

best regards,
Florian Pflug