On Thu, 22 Jun 2006, Jonah H. Harris wrote: > Not in all systems. A few now perform in-memory UNDO and only write > it to disk if and when it is required.
Interesting... > > > Overwriting MVCC comes with its own baggage. Ask any Oracle user about > > error ORA-01555[1]. There's also the added cost of managing the UNDO logs, > > the cost of jumping around between files to get row versions and so on. > > This seems to be going in the direction of our common MySQL > discussions; relying on old failures and mistakes to base our > assumptions on the current version. Please stay apprised of current > developments in other systems. Erm. Perhaps a poor example as I was not trying to put Oracle in a poor light. Rather, I was trying to point out that each method has its disadvantages. If the update in place method has no detractions we shouldn't be hanging on to our existing mechanism. > > J. Gray & A Reuter, Transaction Processing: Concepts and Techniques > > Pretty much older than dirt, discusses locking, and barely touches on > MVCC. Still has some good concepts though. The really useful section of this book is the discussion of snapshot isolation. That's the important thing here. Conceivably we could have a higher performance storage system but, IMHO, it must implement snapshot isolation. Thanks, Gavin ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
