| From: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
|---|---|
| To: | Mike Rylander <mrylander(at)gmail(dot)com> |
| Cc: | "Florian G(dot) Pflug" <fgp(at)phlo(dot)org>, Csaba Nagy <nagy(at)ecircle-ag(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Gregory Stark <stark(at)enterprisedb(dot)com>, postgres hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: CLUSTER and MVCC |
| Date: | 2007-03-09 15:52:36 |
| Message-ID: | 45F182C4.8090709@enterprisedb.com |
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| Lists: | pgsql-hackers |
Mike Rylander wrote:
> On 3/9/07, Florian G. Pflug <fgp(at)phlo(dot)org> wrote:
>> Couldn't HOT in principle deal with this? Let's say you have two
>> long-running
>> transactions, which see row versions A and D. While those transactions
>> are running, the row is constantly updated, leading to row versions B,
>> C (before
>> the second long-running transaction started), D, E, F, ... Z.
>> Now, the versions B,C,E,F,...Z could be removed by HOT or vacuum,
>> because they
>> are not currently visible, nor will they ever become visible because
>> they are
>> already deleted.
>
> Couldn't they (or at least one of them) become visible due to
> SAVEPOINT rollback?
You wouldn't remove tuples with an uncommited xmax, of course.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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