Re: Prepared transactions vs novice DBAs, again

Jeff Davis wrote:
> On Wed, 2009-04-22 at 21:58 +0300, Heikki Linnakangas wrote:
>> Tom Lane wrote:
>>> Does a prepared xact still block vacuum cleanup in HEAD, or has that
>>> been fixed since 8.2?
>> It still does. A prepared xact is just like a idle-in-transaction 
>> backend as far as vacuum is concerned.
> 
> I thought idle transactions generally have released all their snapshots
> (where possible), thus allowing VACUUM to work. I would think something
> similar could work for prepared transactions.

If the prepared transaction has modified any rows (as it typically has, 
or you wouldn't bother with 2PC to begin with), its XID is on disk. We 
can't advance OldestXmin beyond that.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com