> If PostgreSQL wants to stay MVCC, then we should imho forget
> "overwriting smgr" very fast.
>
> Let me try to list the pros and cons that I can think of:
> Pro:
> no index modification if key stays same
> no search for free space for update (if tuple still
> fits into page)
> no pg_log
> Con:
> additional IO to write "before image" to rollback segment
> (every before image, not only first after checkpoint)
> (also before image of every index page that is updated !)
I don't think that Oracle writes entire page as before image - just
tuple data and some control info. As for additional IO - we'll do it
anyway to remove "before image" (deleted tuple data) from data files.
Vadim