On Mon, Aug 10, 2015 at 5:48 PM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> Alexander Korotkov <a.korot...@postgrespro.ru> writes: > > On Mon, Aug 10, 2015 at 1:12 PM, Petr Jelinek <p...@2ndquadrant.com> > wrote: > >> I don't understand this, there is already AmRoutine in RelationData, why > >> the need for additional field for just amsupport? > > > We need amsupport in load_relcache_init_file() which reads > > "pg_internal.init". I'm not sure this is correct place to call > am_handler. > > It should work in the case of built-in AM. But if AM is defined in the > > extension then we wouldn't be able to do catalog lookup for am_handler on > > this stage of initialization. > > This is an issue we'll have to face before there's much hope of having > index AMs as extensions: how would you locate any extension function > without catalog access? Storing raw function pointers in pg_internal.init > is not an answer in an ASLR world. > > I think we can dodge the issue so far as pg_internal.init is concerned by > decreeing that system catalogs can only have indexes with built-in AMs. > Calling a built-in function doesn't require catalog access, so there > should be no problem with re-calling the handler function by OID during > load_relcache_init_file(). > That should work, thanks! Also we can have SQL-visible functions to get amsupport and amstrategies and use them in the regression tests. > We could also have problems with WAL replay, though I think the consensus > there is that extension AMs have to use generic WAL records that don't > require any index-specific replay code. > Yes, I've already showed one version of generic WAL records. The main objecting against them was it's hard insure that composed WAL-record is correct. Now I'm working on new version which would be much easier and safe to use. ------ Alexander Korotkov Postgres Professional: http://www.postgrespro.com The Russian Postgres Company
