| Subject | Re: [firebird-support] Re: Firebird roll forward logging information |
|---|---|
| Author | unordained |
| Post date | 2004-04-25T08:11:07Z |
Hmmm.
a) Don't interbase/firebird have "shadow files" they can write, to create a backup copy on-the-fly,
more or less?
b) Most places take for granted that a backup is a snapshot, and you schedule your backups to
minimize loss, knowing you're not eliminating it. How does that fit in?
c) His solution for "undoing a user's damage" is really not good. The changes would not be stored
as "a = a + 20"; instead they would be stored as "bob said: a = 34", then "larry said: a = 54" --
removing "bob"'s changes will only make larry's even worse. (That's the simple case -- usually,
it's much worse, with entire decision chains depending on the data's "current state" at the time
decisions are being made. Changing history means rewriting history from that point forward.) You
can move forward up until the point of failure, but beyond that, you're toast. At most, you're
slightly reducing the cost of using a backup, a sort of "interpolation" of possible points in time.
You can't eliminate the cost though.
-Philip
---------- Original Message -----------
From: "Johan van Zyl" <johan@...>
To: <firebird-support@yahoogroups.com>
Sent: Sat, 24 Apr 2004 20:48:01 +0200
Subject: [firebird-support] Re: Firebird roll forward logging information
a) Don't interbase/firebird have "shadow files" they can write, to create a backup copy on-the-fly,
more or less?
b) Most places take for granted that a backup is a snapshot, and you schedule your backups to
minimize loss, knowing you're not eliminating it. How does that fit in?
c) His solution for "undoing a user's damage" is really not good. The changes would not be stored
as "a = a + 20"; instead they would be stored as "bob said: a = 34", then "larry said: a = 54" --
removing "bob"'s changes will only make larry's even worse. (That's the simple case -- usually,
it's much worse, with entire decision chains depending on the data's "current state" at the time
decisions are being made. Changing history means rewriting history from that point forward.) You
can move forward up until the point of failure, but beyond that, you're toast. At most, you're
slightly reducing the cost of using a backup, a sort of "interpolation" of possible points in time.
You can't eliminate the cost though.
-Philip
---------- Original Message -----------
From: "Johan van Zyl" <johan@...>
To: <firebird-support@yahoogroups.com>
Sent: Sat, 24 Apr 2004 20:48:01 +0200
Subject: [firebird-support] Re: Firebird roll forward logging information
> >From Clarion Newsgroup------- End of Original Message -------
>
> I was following the Jack T. messages about a lack of roll forward
> logging in Firebird.
>
> Dalton Calford wrote this article many moons ago
> http://firebird.sourceforge.net/index.php?op=useful&id=calford_1
>
> I have yet to find any of the items he said would be posted. But the
> article does give information about the problem and a possible
> solution for Firebird.
>
> =====================
> Johan van Zyl
> JVZ Systems CC
> Box 3469
> Somerset West
> 7129
> 082 875 4238
> 021 8517205
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