Re: vacuum, performance, and MVCC

Jonah H. Harris wrote:
> On 6/22/06, Gavin Sherry <swm@linuxworld.com.au> wrote:

> >When an update occurs, the existing row version is
> >copied to te UNDO file
> 
> Not in all systems.  A few now perform in-memory UNDO and only write
> it to disk if and when it is required.

How does that work?  If the last transaction is not finished after it
wrote the tuple when the power goes out, and the UNDO is not written to
disk either, how do you reconstruct the tuple at all?

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.