RE: [HACKERS] Plans for solving the VACUUM problem

[Mikheev, Vadim]

> 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

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