Re: implementing a database log

From: David BL <>
Date: Tue, 22 Apr 2008 00:04:25 -0700 (PDT)
Message-ID: <>

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
> 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

  1. logical changes aren't always idempotent
  2. 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

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