From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru> |
Cc: | Petr Jelinek <petr(at)2ndquadrant(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Robert Haas <robertmhaas(at)gmail(dot)com> |
Subject: | Re: WIP: Rework access method interface |
Date: | 2015-08-10 14:48:48 |
Message-ID: | 13968.1439218128@sss.pgh.pa.us |
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Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru> writes:
> On Mon, Aug 10, 2015 at 1:12 PM, Petr Jelinek <petr(at)2ndquadrant(dot)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().
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.
regards, tom lane
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