Re: Sequence Access Method WIP

On Thu, Jan 22, 2015 at 10:50 AM, Heikki Linnakangas
<hlinnakangas@vmware.com> wrote:
> On 01/12/2015 11:33 PM, Petr Jelinek wrote:
>> Second patch adds DDL support. I originally wanted to make it
>> CREATE/DROP SEQUENCE ACCESS METHOD... but that would mean making ACCESS
>> a reserver keyword so I went for CREATE ACCESS METHOD FOR SEQUENCES
>> which does not need to change anything (besides adding METHOD to
>> unreserved keywords).
>> The DDL support uses the DefineStmt infra with some very small change as
>> the sequence ams are not schema qualified, but I think it's acceptable
>> and saves considerable amount of boilerplate.
>
> Do we need DDL commands for this at all? I could go either way on that
> question. We recently had a discussion on that wrt. index access methods
> [1], and Tom opined that providing DDL for creating index access methods is
> not worth it. The extension can just insert the rows into pg_seqam with
> INSERT. Do we expect sequence access methods as extensions to be more
> popular than index access methods? Maybe, because the WAL-logging problem
> doesn't exist. But OTOH, if you're writing something like a replication
> system that needs global sequences as part of it, there aren't that many of
> those, and the installation scripts will need to deal with more complicated
> stuff than inserting a row in pg_seqam.

I think the main reason we don't need DDL for pg_am is because there's
no real hope of anybody actually inserting anything in there whether
we have a command for it or not.  If we actually expect this to be
used, I think it should probably have some kind of DDL, because
otherwise what will pg_dump emit?  "Nothing" is bad because then dumps
won't restore, and "direct inserts to pg_seqam" doesn't seem great
either.

-- 
Robert Haas
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