From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Kevin Grittner <kevin(dot)grittner(at)wicourts(dot)gov>, Joachim Wieland <joe(at)mcknight(dot)de>, Noah Misch <noah(at)leadboat(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Snapshot synchronization, again... |
Date: | 2011-02-22 00:19:54 |
Message-ID: | 1298333744-sup-4262@alvh.no-ip.org |
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Lists: | pgsql-hackers |
Excerpts from Tom Lane's message of lun feb 21 21:00:19 -0300 2011:
> Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> > Actually this seems rather difficult to do, because in order to invoke
> > the function that imports the snapshot, you have to call SELECT, which
> > acquires a snapshot beforehand. So when we actually import the
> > passed-in snapshot, there's already a snapshot set. This is odious but
> > I don't see a way around that -- other than adding special grammar
> > support which seems overkill.
>
> No, I don't think it is. The alternative is semantics that are
> at least exceedingly ugly, and very possibly flat-out broken.
> To take just one point, you have no way at all of preventing the
> transaction from having done something else using its original
> snapshot.
That's true too. So let's discuss the syntax. Maybe
START TRANSACTION SNAPSHOT '\xdeadbeef';
This kind of extension seems ugly though; maybe we should consider
START TRANSACTION (snapshot='\xdeadbeef');
(like VACUUM, EXPLAIN and COPY) or some such?
I don't think we need another "top-level" command for this.
--
Álvaro Herrera <alvherre(at)commandprompt(dot)com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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