On Mon, Aug 10, 2015 at 5:48 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Alexander Korotkov <a.korotkov@postgrespro.ru> writes: > On Mon, Aug 10, 2015 at 1:12 PM, Petr Jelinek <petr@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
