Re: implementing a database log

On Apr 22, 7:56 am, paul c <toledoby...@xxxxxxxx> wrote:

Several advantages of logical logging, not the only ones, I'm sure:

1) Likely more insensitive to future changes in physical
organization/operations.

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

a) logical changes aren't always idempotent

b) 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.

.