Re: Replication Node Identifiers and crashsafe Apply Progress

On 2013-11-21 08:22:05 -0500, Robert Haas wrote:
> On Thu, Nov 21, 2013 at 6:15 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> >> > WRT performance: I agree that fixed-width identifiers are more
> >> > performant, that's why I went for them, but I am not sure it's that
> >> > important. The performance sensitive parts should all be done using the
> >> > internal id the identifier maps to, not the public one.
> >>
> >> But I thought the internal identifier was exactly what we're creating.
> >
> > Sure. But how often are we a) going to create such an identifier b)
> > looking it up?
>
> Never. Make that the replication solution's problem. Make the core
> support deal only with UUIDs or pairs of 64-bit integers or something
> like that, and let the replication solution decide what they mean.

I think we're misunderstanding each other. I was commenting on your fear
that strings longer than NAMEDATALEN or something would be bad for
performance - which I don't think is very relevant because the lookups
from "public" to "internal" identifier shouldn't be in any performance
critical path.

I personally would prefer a string because it'd allow me to build an
identifier using the criterions I'd originally outlined outside of this
infrastructure.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services