A long time ago, in a galaxy far, far away, kevin@sysexperts.com (Kevin Brown) wrote:
> Bruce Momjian wrote:
>>
>> OK, once we have PITR, will anyone want incremental backups?
>
> None of my database references (Date's "Introduction to Database
> Systems" and Garcia-Molina's "Database Systems - The Complete Book",
> in particular) seem to talk about PITR at all. At least, there's no
> index entry for it. And a google search for "point in time recovery"
> yields mostly marketing fluff.
Well, from an "academic DBMS" standpoint, it isn't terribly
interesting, since it involves assumptions of messy imperfection that
academics prefer to avoid.
And that's not intended to insult the academics; it is often
reasonable to leave that "out of scope" much as an academic OS
researcher might prefer to try to avoid putting attention on things
like binary linkers, text file editors, and SCM systems like CVS,
which, while terribly important from a practical standpoint, don't
make for interesting OS research.
> Is there a good reference for this that someone can point me to?
> I'm interested in exactly how it'll work, especially in terms of how
> logs are stored versus the main data store, effects on performance,
> etc.
>
> Thanks, and sorry for the newbie question. :-(
Unfortunately, the best sources I can think of are in the "O-Word"
literature, and the /practical/ answers require digging into really
messy bits of the documentation.
What it amounts to is that anyone that isn't a "near-O*****-guru" would be
strongly advised not to engage in PITR activity.
It doesn't surprise me overly that the documentation is poor: those
that can't figure it out despite the challenges almost surely
shouldn't be using the functionality...
What PITR generally consists of is the notion that you want to recover
to the state at a particular moment in time.
In O*****-nomenclature, this means that you recover as at some earlier
moment for which you have a good backup, and then re-apply changes,
which in their terms, are kept in "archive logs," which are somewhat
analagous to WAL files.
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