Re: implementing a database log
Date: Tue, 22 Apr 2008 00:04:25 -0700 (PDT)
On Apr 22, 7:56 am, paul c <toledoby..._at_ac.ooyah> wrote:
> Several advantages of logical logging, not the only ones, I'm sure:
> 1) Likely more insensitive to future changes in physical
> 2) Potential to reconstruct old db values with additional constraints
> applied (I don't know how many times this would have avoided much more
> awkward surprise requirements).
> 3) Ability to shadow via another physical db, eg., for read-only audit
> or various performance requirements (my favourite advantage, maybe most
> people would favour #1.)
There are also disadvantages to logical logging
- logical changes aren't always idempotent
- there are many forms of logical changes, whereas physical changes to a page are always assumed to simply be assignments to a range of bytes within the page.
Both of these create a lot of complexity. I think physical logging is much easier to implement. Received on Tue Apr 22 2008 - 09:04:25 CEST