Re: Some ideas about Vacuum

Tom Lane escribió:
> Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> > Tom Lane escribió:
> >> It would only be useful to have one per spindle-dedicated-to-WAL, so
> >> tying the division to databases doesn't seem like it'd be a good idea.
>
> > Keep in mind that there are claims that a write-cache-enabled
> > battery-backed RAID controller negates the effect of a separate spindle.
>
> Possibly true, but if that's the underlying hardware then there's no
> performance benefit in breaking WAL up at all, no?

Selective PITR shipping.

> > My point, rather, is that with this sort of setup it would be easier to
> > do per-database PITR shipping, and one database's WAL activity would not
> > affect another's (thus hosting providers are happier -- high-rate
> > customer A need not affect low-budget customer B).
>
> You won't get far with that because of the shared catalogs. In
> particular, most DDL operations these days touch pg_shdepend ...

That's why you log shared activity to another WAL stream, and ship that
to everyone, while the other databases' WAL streams are shipped only to
the interested slaves.

--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.