Re: Some ideas about Vacuum

Heikki Linnakangas escribió:

> I don't think it's going to work too well, though, not without major 
> changes at least. What would happen when you restore a PITR backup of just 
> one database? Would the other databases still be there in the restored 
> cluster? What state would they be in? After restoring one database, and 
> doing some stuff on it, could you ever "merge" those changes with the rest 
> of the cluster?

Well, a PITR slave, after you change it, cannot be brought in sync with
the master.  This is not different.

If you replicate a single database's stream, the other databases should
not be there.  My idea is that a slave could request multiple databases'
streams.  The ability to do it is needed anyway, to follow both the
basic database stream and the shared stream.

> Mind you, there's more things shared between databases than the shared 
> catalogs. clog for example.

Sure --- my original proposal mentioned the use of the shared WAL stream
for global objects (though I didn't mention pg_clog, but surely it had
better be there).

> For more usefulness, we'd need to keep databases more separate from each 
> other than we do now. Databases would need to have their own transaction 
> counters, for example.

Hmm, why?  Perhaps you are right but I don't see the reason.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support