On Tue, Apr 12, 2016 at 9:21 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Michael Paquier <michael.paqu...@gmail.com> writes: >> What I thought we should be able to do with that should not be only >> limited to indexes, aka to: >> - Be able to register and log full pages >> - Be able to log data associated to a block >> - Be able to have record data >> - Use at recovery custom routines to apply those WAL records > > I'm not following your distinction between a "page" and a "block", > perhaps.
s/block/page/. Sorry for the confusion. > Also, the entire point here is that extensions DON'T > get to have custom apply routines, because we have no way for > replay to know about such apply routines. (It surely cannot look > in the catalogs for them, but there's no other suitable infrastructure > either.) In turn, that means there's little value in having any custom > data associated with the WAL records. Well, yes, the startup process has no knowledge of that. That's why it would need to go through a hook, but the startup process has no knowledge of routines loaded via _PG_init perhaps? I recall that it loaded them. The weakness with this interface is that one needs to be sure that this hook is actually loaded properly. > If we ever solve the registering-custom-replay-routines conundrum, > it'll be time to think about what the frontend API for that ought > to be. But this patch is not pretending to solve that, and indeed is > mainly showing that it's possible to have a useful WAL extension API > that doesn't require solving it. Yep. I am not saying the contrary. This patch solves its own category of things with its strict page-level control. > In any case, the existence of this API doesn't foreclose adding > other APIs (perhaps backed by other RM_GENERIC_ID WAL record types) > later on. So I don't think we need to insist that it do everything > anyone will ever want. Perhaps I am just confused by the interface. Linking the idea of a page delta with GenericXLogRegister is not that intuitive, knowing that what it should actually be GenericXLogRegisterBuffer and we should have GenericXLogAddDelta, that applies a page difference on top of an existing one. -- Michael -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
