Re: [PATCH 2/2] Add a new function pg_relation_by_filenode to lookup up a relation given the tablespace and the filenode OIDs

On Monday, September 17, 2012 12:35:32 AM Tom Lane wrote:
> Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> > This requires the previously added RELFILENODE syscache.
>
> [ raised eyebrow... ] There's a RELFILENODE syscache? I don't see one,
> and I doubt it would work given that the contents of
> pg_class.relfilenode aren't unique (the zero entries are the problem).
Well, one patch upthread ;). It mentions the problem of it not being unique due
to relfilenode in (reltablespace, relfilenode) being 0 for shared/nailed
catalogs.

I am not really sure yet how big a problem for the caching infrastructure it is
that values that shouldn't ever get queried (because the relfilenode is
actually different) are duplicated. Reading code about all that atm.

Robert suggested writing a specialized cache akin to whats done in
attoptcache.c or such.

I haven't formed an opinion on whats the way forward on that topic. But anyway,
I don't see how the wal decoding stuff can progress without some variant of
that mapping, so I sure hope I/we can build something. Changing that aspect of
the patch should be trivial...

Greetings,

Andres
--
Andres Freund http://www.2ndQuadrant.com/
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