Date: Tue, 28 Jan 2020 07:33:17 -0600
From: Justin Pryzby <pryzby@telsasoft.com>
To: pgsql-hackers@postgresql.org
Cc: Andres Freund <andres@anarazel.de>
Subject: tableam options for pg_dump/ALTER/LIKE
Message-ID: <20200128133317.GZ13621@telsasoft.com>
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I made these casual comments.  If there's any agreement on their merit, it'd be
nice to implement at least the first for v13.

In <20190818193533.GL11185@telsasoft.com>, I wrote: 
>  . What do you think about pg_restore --no-tableam; similar to 
>    --no-tablespaces, it would allow restoring a table to a different AM:
>    PGOPTIONS='-c default_table_access_method=zedstore' pg_restore --no-tableam ./pg_dump.dat -d postgres
>    Otherwise, the dump says "SET default_table_access_method=heap", which
>    overrides any value from PGOPTIONS and precludes restoring to new AM.

That appears to be a trivial variation on no-tablespace:

        /* do nothing in --no-tablespaces mode */
        if (ropt->noTablespace)
                return;

>  . it'd be nice if there was an ALTER TABLE SET ACCESS METHOD, to allow
>    migrating data.  Otherwise I think the alternative is:
> 	begin; lock t;
> 	CREATE TABLE new_t LIKE (t INCLUDING ALL EXCLUDING INDEXES) USING (zedstore);
> 	INSERT INTO new_t SELECT * FROM t;
> 	for index; do CREATE INDEX...; done
> 	DROP t; RENAME new_t (and all its indices). attach/inherit, etc.
> 	commit;

Ideally that would allow all at once various combinations of altering
tablespace, changing AM, clustering, and reindexing, like what's discussed
here:
https://www.postgresql.org/message-id/flat/8a8f5f73-00d3-55f8-7583-1375ca8f6a91@postgrespro.ru

>  . Speaking of which, I think LIKE needs a new option for ACCESS METHOD, which
>    is otherwise lost.