On 6/22/06, Tom Lane <[EMAIL PROTECTED]> 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            | [EMAIL PROTECTED]
Iselin, New Jersey 08830            | http://www.enterprisedb.com/

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TIP 9: In versions below 8.0, the planner will ignore your desire to
      choose an index scan if your joining column's datatypes do not

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