Subject: Re: Closing inactive connections OR user connections
From: Brian Hirt <bhirt@mobygames.com>
To: "scott.marlowe" <scott.marlowe@ihs.com>
Cc: Medi Montaseri <medi.montaseri@intransa.com>,
	Neil Conway <neilc@samurai.com>, Francisco Reyes <lists@natserv.com>,
	pgsql General List <pgsql-general@postgresql.org>
In-Reply-To: <Pine.LNX.4.33.0211201609270.21609-100000@css120.ihs.com>
References: <Pine.LNX.4.33.0211201609270.21609-100000@css120.ihs.com>
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Date: 20 Nov 2002 16:16:59 -0700
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Scott,

You did a rollback on the transaction, so the delete was never commited.
I hope you aren't expecting vacuum to delete uncommited rows from the
database, are you?

--brian

On Wed, 2002-11-20 at 16:12, scott.marlowe wrote:
> On Wed, 20 Nov 2002, Medi Montaseri wrote:
> 
> > Its my understanding that vacuum actually removes tuples that have been 
> > updated or deleted.
> > Sort of like emptying your trash .... whence a tuple has been removed, 
> > no rollback can set the
> > state back. If you have logically removed a tuple (not vacuumed yet), 
> > then one can rollback,
> > but if you vacuum then you can not rollback.
> > 
> > Now suppose transaction A decides to delete some tuples, a vacuum job 
> > comes along and
> > deletes things (in parallel), trans A decides to rollback....engines who 
> > support parallel
> > vacuum-ing and transactions such as PG 7.2 better have a way of 
> > protecting themselves
> > against this....
> > 
> > Correct me if ...
> 
> Yes, you are wrong.  Postgresql's vacuuming does NOT free tuples that are 
> still in a transaction, hence a full vacuum will hand waiting for the 
> transaction to complete or roll back.  A normal 7.2 vacuum will simply 
> skip the in transaction tuples.
> 
> For proof, try this:  (Note A> and B> are used to represent two different 
> sessions)
> 
> A> create table test (a text, id int);
> A> insert into test (a,id) values ('abc',123);
> A> begin;
> A> delete from test where id=123;
> B> vacuum;
> A> rollback;
> A> select * from test;
> a  |  id
> --------
> abc| 123
> 
> Still there.
> 
> 
> > 
> > Neil Conway wrote:
> > 
> > >Medi Montaseri <medi.montaseri@intransa.com> writes:
> > >  
> > >
> > >>I think from the data integrity point of view, vacuum is more
> > >>important than vacuum full.
> > >>    
> > >>
> > >
> > >Why would VACUUM have any effect on data integrity, either positive or
> > >negative?
> > >
> > >Cheers,
> > >
> > >Neil
> > >
> > >  
> > >
> > 
> > 
> > 
> > 
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-- 
Brian Hirt <bhirt@mobygames.com>