Re: vacuum, performance, and MVCC

On 6/22/06, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> The Oracle design has got other drawbacks: if you need to access a row
> version other than than the very latest, you need to go searching in the
> rollback segments for it.

There are ways to implement this functionality without implementing it
exactly as Oracle has.

> Plus there's the old bugaboo that long-running transactions
> require indefinite amounts of rollback space, and Oracle is
> apparently unable to enlarge that space on-the-fly.

This has actually gotten much better in recent versions.

> Basically there's no free lunch: if you want the benefits of MVCC it's
> going to cost you somewhere.

Surely. Our MVCC design is great for SELECT, INSERT, and for the most
part, DELETE. However, I'm confident that we can build a hybrid MVCC
model that takes some of the pain out of UPDATE without having to
overcomplicate VACUUM or violate patents.

--
Jonah H. Harris, Software Architect | phone: 732.331.1300
EnterpriseDB Corporation | fax: 732.331.1301
33 Wood Ave S, 2nd Floor | jharris(at)enterprisedb(dot)com
Iselin, New Jersey 08830 | http://www.enterprisedb.com/