Re: subtransactions -- storage manager

Alvaro, is this ready to be applied?

---------------------------------------------------------------------------

Alvaro Herrera wrote:
> Hackers,
>
> This patch adds subtransaction support into the storage manager.  Files
> created or dropped inside a subtransaction are correctly dealt with at
> subtransaction commit or abort.
>
> This works:
> create table foo (a int);
> create table foo2 (a int);
> begin;
>     begin;
>         create table bar (a int);
>         select relfilenode, relname from pg_class where relname in ('foo', 'bar');
>         drop table foo2;
>     rollback;
>     drop table foo;
>     create table baz (a int);
>     select relfilenode, relname from pg_class where relname='baz';
> commit;
>
> At this point, the files for "bar" and "foo" have disappeared, while
> "foo2" and "baz" remain.  (Note however that the catalog entries are not
> correct -- this is because we don't have correctly recorded results in
> pg_clog.)
>
> While making this I realized I had made a mistake regarding portal
> memory, so I also correct it with this patch.  As a side effect, the
> following works;
>
> begin;
>     begin;
>         declare foo cursor for select 1;
>     commit;
>     begin;
>         declare bar cursor for select 1;
>     rollback;
>     fetch all from foo;        -- returns 1 row
>     fetch all from bar;        -- no such cursor
> rollback;
>
> (This patch will only apply cleanly with the previous patch applied.)
>
>
>
> Still missing:
>
> - support for prepared statements, async notifies.  Easy.
> - support for on commit actions.  Not sure.
> - support for deferred triggers.  Not so easy, maybe hard.
> - correct LWLock handling.  Should be easy (release them all on abort)
> - correct regular lock handling.  Not so easy.
> - pg_clog/pg_subtrans.  Need a solution.
>
>
> PS: somehow I managed to get tired of the phrase "nested transactions"
> and I'm using the term "subtransactions" instead.  In my head they are
> the same thing ...
>
> --
> Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
> Hi! I'm a .signature virus!
> cp me into your .signature file to help me spread!

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