Re: CLUSTER and MVCC

Florian G. Pflug 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.

Yes, you could detect that but you'd need a global view of all snapshots 
in the system. I just posted a reply in this thread with more details..

It's not just with HOT, it's the way we determine that a tuple is 
vacuumable in general.

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