Re: Problem with txid_snapshot_in/out() functionality

From: Andres Freund <andres(at)2ndquadrant(dot)com>
To: Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Jan Wieck <jan(at)wi3ck(dot)info>, PostgreSQL Development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Problem with txid_snapshot_in/out() functionality
Date: 2014-04-14 09:32:56
Message-ID: 20140414093256.GT4161@awork2.anarazel.de
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On 2014-04-14 12:15:30 +0300, Heikki Linnakangas wrote:
> Hmm. There's a field in GlobalTransactionData called locking_xid, which is
> used to mark the XID of the transaction that's currently operating on the
> prepared transaction. At prepare, that ensures that the transaction cannot
> be committed or rolled back by another backend until the original backend
> has cleared its PGPROC entry. At COMMIT/ROLLBACK PREPARED, it ensures that
> only one backend can commit/rollback the transaction.
>
> I wonder why we don't use a VirtualTransactionId there.

I wondered about that previously as well. My bet it's because the 2pc
support arrived before the virtualxact stuff...

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

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