Re: rmgr hooks (v2)

On Wed, 2009-01-21 at 18:38 +0200, Heikki Linnakangas wrote:
> Simon Riggs wrote:
> > So you *must* replay catalog entries and recreate the original catalog
> > in exact synchronisation with reading WAL files. Recreating the catalog
> > can only be done by Postgres itself.
>
> The startup process doesn't have a relcache, so this rmgr patch is
> nowhere near enough to enable that. If I understood correctly, the hot
> standby patch doesn't change that either.

The answer to this question was that it doesn't need a relcache, though
perhaps it might be desirable.

Catalog tables are scanned with SnapshotNow and so will work correctly
without that machinery. We already rely on this within the existing code
to update flat files towards the end of recovery.

It is true that you can't look at user data, but then I can already do
that with Hot Standby, so the plugin isn't needed for that.

--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support